Introduction
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Gene – basic DNA unit that results in a trait
Genetics – the study of the way an individuals’ traits are transmitted from one generation to
the next; the study of heredity
Classic Mendelian Genetics – one gene = one trait = one disease
Genome – sum total of all DNA molecules in an individual
Genomics – the study of all the genetic content/genome within an individual
o Includes identifying, mapping, determining function, and how genes interact with each
other + the environment
In complex disease, genes interact with each other and the environment to result in disease
Underlying Principle of Genetic Disease
o Genetic Disease – the variation/mutation that caused the disease must be in the
germline (gametes) so that it is inherited in the next generation
o Variations that occur in the somatic cells may result in disease (ex: tumor), but if the
mutation is not in the germline, then it is not passed to the next generation = NOT
hereditary
Basic Cell Biology + Gene Structure
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Central Dogma
o DNA molecules are the information for biological traits, which are transcribed into
mRNA, which serves as the template to be translated into proteins, which manifest into
biological structures and function.
DNA – macromolecule made up of nucleotides
Each nucleotide contains a 5-carbon sugar, a nitrogenous base, and a phosphate group
o 5-carbon sugar
o Nitrogenous base – A, T (U), G, and C
 Purines are A and G
 Pyrimidines are C, T, and U
o Phosphate group – on the 5’ end; allows the attachment and connection of additional
nucleotides with a 3’-5’ phosphodiester bond between each nucleotide
DNA Backbone – alternating sugar and phosphates
o Phosphate group attached to carbon 5. Carbon 3 has a free hydroxyl group where
another nucleotide’s phosphate can connect to form the phosphodiester bond
Directionality – 5’ end is the beginning/top; 3’ is bottom/only free end where more nucleotides
can attach
o Five prime end is first
Antiparallel – nitrogenous bases bind together to form the middle ladder part of the DNA
double helix with hydrogen bonds in a way that the 5’ and 3’ ends are in opposite directions
Complementarity – the nitrogenous bases fit like puzzle pieces
o Adenine always binds with thymine
o Guanine always binds with cytosine
o G + C are triple bonded, and those base pairs are stronger/harder to break/require
more energy
DNA Packaging
o Histones – proteins that DNA wraps around
o Nucleosomes – 8 histones in a core and 140-150bp of DNA wrapped around
o Solenoid – 30nm fiber of 6 nucleosomes wrapped around themselves
o Chromatin – fiber of solenoids wrapped around themselves; appears as a hazy cloud
within the nucleus
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 X-shaped only appears during metaphase of mitosis
Cell Cycle
o G1 = gap 1; prep for replication
o S = synthesis; DNA replication
o G2= checks to make sure DNA was replicated properly
o Mitosis = cell division into 2 genetically identical daughter cells
Central Dogma
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DNA Replication – in nucleus
o Replication – the synthesis of new DNA strands, using old strands as templates to copy
 Goal to double the DNA content so you can divide the cell into 2 identical
daughter cells
 Takes place during the S phase (synthesis phase) of cell cycle
o Semi-conservative
 Two complementary, antiparallel DNA strands unwind and individually act as
templates for the synthesis of new DNA strands.
 Each of the daughter DNA duplexes contain one original parental DNA strand
and one new DNA strand which are structurally identical to the parental DNA
duplex
 Half of the new DNA is parental and half of it is new.
o DNA helicase unwinds the parental double helix DNA molecule and creates a
replication fork
o Single stranded DNA is pretty unstable so there are proteins to stabilize it
o Primase creates a RNA primer that triggers the DNA polymerase to work and create the
new DNA strand
o DNA polymerase adds on new nucleotides to the 3’ end based on the template of the
parental strand; travels building in 5’ to 3’ direction
 Leading strand – travels down synthesizing continuously
 Lagging strand – synthesized discontinuously (bc polymerase can only travel 5’-3’
so it is traveling backwards kinda) and creates Okazaki fragments of new DNA
o DNA ligase joins the Okazaki fragments together by creating phosphodiesterase bonds
between gaps of nucleotides
o DNA replication is bi-directional and has multiple origins of replication
DNA Transcription – in nucleus
o Regulatory sequences – help drive transcription; before and after gene sequences
o UTR = untranslated regions which exist on both the 5’ and 3’ ends
o Introns get sliced out bc they INterrupt the sequence of the EXpressed exons
o Transcription – synthesis of mRNA, using DNA as a template to copy
 Occurs throughout the cell cycle
o RNA compared to DNA
 Oxygenated pentose sugar at 2’ carbon
 Uracil instead of thymine
 Single stranded
o Antisense strand – the ONLY DNA strand that serves as a template
o Sense strand – the DNA strand that is NOT copied
 DNA sense strand sequence is IDENTICAL to mRNA sequence
 *except U replaces T*
o RNA polymerase adds nucleotides on the growing 3’ end (5’ to 3’)
o Unidirectional transcription bc single stranded
Not all DNA is transcribed
 Only less than 25% of the entire genome
 Only GENES are transcribed
 Controlled by core promoter and regulatory sequences upstream of gene
o They engage together and with many proteins to create an
environment for RNA polymerase to bind to and begin transcription
 Core promoter – a sequence that is absolutely required in the promoter
for transcription; the location is consistent with every gene
 Promoter proximal elements – DNA sequences upstream of core promoter
that interacts with different proteins to allow for gene expression; they
change/vary with every gene
 Enhancers – sequences that influence the rate of transcription initiation
increasing it; position changes with every gene
 Silencers – influence the rate of transcription by decreasing it
o Transcription produces primary transcript of mRNA
o Post-transcriptional Processing
 5’-capping – 7-methyl guanine is added via 5’ to 5’ phosphate linkage
 Helps stabilize and protect it from degradation by cytoplasmic enzymes
 Helps signal to bind to ribosome
 Poly(A) Tail Addition
 3’ polyadenylation
 An enzyme is signaled to add the poly(A) tail to the 3’ end
 Helps protect it from degradation
 Splicing
 Spliceosome protein complex scans the primary mRNA transcripts until it
encounters a splicing consensus sequence (GU at 5’ end and AG at 3’
end) where it will cut out the intron
 The adjacent exons are then ligated together
Translation – in the cytoplasm
o Post-processing, mRNA travels outside of the nucleus and finds a free ribosome or one
on the rough ER
o Transfer RNA (tRNA) – specific structure that brings amino acids to ribosomes
 The specific amino acid will attach at its 3’ end
 An anticodon is found on the other end
 Complementary triplet pair of nucleotides that will match with a codon
on mRNA
 Anticodon sequence determines which amino acid will be added to the
growing polypeptide chain
o mRNA codons read along CHART to determine amino acid
 ex: mRNA ACG (read on chart) = tRNA UGC = threonine amino acid
o mRNA is threaded through the ribosome as tRNA binds to it (based on anticodons) and
brings an AA to the ribosome to generate a polypeptide chain. This occurs sequentially
as the mRNA travels through the ribosome.
Genome Organization
o 100% replicated
 SINES + LINES make up the dispersed repetitive elements and ~45% of the entire
genome
o ~25% transcribed (exons + introns)
o ~1.5% translated (only exons)
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Satellite DNA (10% of DNA) – repetitive elements/sequences normally found towards the
ends and centromeres that occur together in clusters; differs per person and can be
used for DNA fingerprinting
Most of the “other DNA” serves no known function, but has been selected for
evolutionarily
Dispersed repeats are similar to one another but do not cluster together
Single-copy DNA sequences are unique and dispersed throughout the genome
Coding DNA – sequences that are transcribed AND translated; exons; ~1.5% of genome
Genetic Variation
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Autosome – non-sex chromosome; chromosomes #1-22
Sex chromosome – X + Y
Locus – area of the chromosome that contains genetic information; location of a gene or
sequence on chromosome
o Generic term that can vary in size (nucleotide, gene, etc)
Genetic variations/Polymorphism – differences in DNA sequence; may or may not result in
disease; classified based on size
Mutations – a type of genetic variation that usually results in defective gene expression;
germline or somatic
Hereditary disease – if the mutation is in the germline and can be passed down to the next
generation
Allele – an alternative form of a gene that is located at a specific position on a specific
chromosome
o Ex: maternal, paternal, wild type, normal, mutant, disease-specific
Genotype – the allelic composition of an organism
Phenotype – the physical characteristics of an organism, defined by the genotype
Homozygote – having two copies of the same allele
Heterozygote – having one copy of each allele
Hemizygote – having ONLY one copy of one allele
o Ex: the X or Y chromosomes in males
Types of Mutations
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Silent mutation – single nucleotide change within a coding sequence that does NOT affect the
protein/amino acid sequence produced
Missense mutation – single nucleotide that changes the codon to a single different amino
acid, and therefore changes the protein sequence and possibly the biological trait
o Missense is Misspelled amino acid sequence
o Ex: Sickle Cell Anemia is Glu  Val in codon 6 of beta-globin chain (CTA  CAC)
 Now instead of a polar glutamic acid that allows for the round shape of RBCs,
with valine, the beta globin unit is stickier and create the long, rigid, stick-like,
sicked shape that can block capillaries and impede blood flow
Nonsense mutation - produces one of the three stop codon (UAA, UAG, UGA)
o Non like No like Stop
o Premature stop codon = truncated sequence
Frameshift mutations occur when there is a deletion or insertion that happens at a non-multiple
of three
o ALL amino acids after the insertion/deletion are most likely incorrect
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Splice-site mutation – changes within the consensus sequences (donor = GU; acceptor = AG)
of the splice site; possible that the spliceosome does not cleave where it is supposed to or
cleaves at an extra site
Regulatory element mutation – when mutated, transcription is altered, which can change the
amount of gene product (reduction or increase)
o Key takeaway: you don’t have to have a mutation in the coding region of a gene to
have a disease
Satellite DNA – about 10% genome; small, repetitive elements, usually found near the
centromeres or ends of chromosome
o 2 Types:
 Microsatellite – short tandem repeat polymorphisms; STRP; 1-13bp repeats
 Minisatellite – variable number of tandem repeat polymorphisms; VNTR; 14-500bp
repeats
o Highly polymorphic/very individually variable
o >1000 arrays of VNTRs throughout the genome
o Easy to assay these arrays
o Length varies
o DNA fingerprinting
Trinucleotide repeat – specific type of microsatellite DNA; sequence repeats of 3 nucleotides;
occur normally in some genes
o Expansion of the number of repeats can lead to disease
 PolyQ Disorders
 CAG repeat = glutamine
 Trinucleotide repeats are contained within the coding region
 Ex: Huntington’s Disease
 Non-PolyQ
 Non-CAG repeat
 Repeat can be found in coding region or non-coding region
 Ex: Fragile X Syndrome
Gene Copy Number Variation
o An entire gene copy that ranges in its number leads to dosage sensitivity
 Normally we have 2 copies of every gene in our diploids = average protein
product
 Extra copy of gene = increased dosage = 150% protein production
 Loss of copy of gene = decreased dosage = 50% protein production
Causes of Mutations
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Spontaneous
o Replication errors
o Deamination (amino group is lost; C is converted to T)
o Reactive oxygen species (ROS; by products of cellular metabolism that can react +
bind to DNA, causing it to change)
Induced (Exogenous)
o Chemicals (ex: carcinogens like tobacco smoke)
o Radiation
 Ionizing (x-rays) – cause single or double strand breaks
 Non-ionizing (UV) – cause cross-linking on adjacent thymines; forming a
covalently-linked thymine dimer that causes a kink within the DNA structure that
can’t be unwound and thus can’t be replicated
Blocks replication and the cell may die
Or the cell will replicate incorrectly and use another nucleotide that
doesn’t match the thymine
Key Takeaway: Mutations occur all the time in humans. These must be fixed to avoid genome
instability
Paternal Age Effect – older men have a higher incidence of children with single gene disorders
due to accumulation of mutations in sperm stem cells
o Over a lifetime, the sperm stem cells can have accumulation of mutations that lead to
increased risk for single gene disorders in children of older men. This mutation would be
considered a new mutation bc the dad didn’t have the mutation, but his germline
developed it and passed it on to the next generation.
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DNA Repair
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DNA damage occurs every cell cycle, but we have many repair pathways. They are based on
the type of damage that they recognize and repair as well as the types of proteins they use
Mismatch repair (MMR) – repairs a wrong nucleotide pairing, often during replication
Nucleotide Excision repair (NER) – repairs damage that results in distorted helix; typically from
UV radiation = correcting the thymine dimer
o Xeroderma Pigmentosum – mutation of the genes that create proteins involved in NER
repair
General Process: proteins scan the DNA and recognize the damage, then they signal out for
other proteins to come, the damage is cleaved out and digested, then DNA polymerase
comes in to refill the gap
o Inability to repair DNA is often linked to increased risk of cancer
Biomolecular Assays
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Western blot detects protein
o Separation based on size within gel electrophoresis
 Take the patient DNA sample, extract all of the proteins and load it into the wells.
An electric current is run through the gel of buffer liquid with neg charge at the
top and pos at the bottom
o Can see differences in:
 Size
 Smaller proteins move faster down the gel (like crumbs in a chip bag)
 Amount
 Thickness/thinness of protein band
 Presence/Absence
 Marked via antibody
o Detection is with an antibody
o Pros:
 Can detect loss of protein, differences in amount of protein, or DNA mutations
that affect the size of protein
 Detects:
 nonsense mutation in coding DNA
o truncated or no protein
 promoter mutation in DNA
o affects mRNA and protein
o Cons
 Must know what the gene is that you’re analyzing (confirmatory)
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 Must have a good antibody
 Can be time consuming (takes about 2 days)
o Clinical Ex:
 Muscular dystrophies can be detected
 Mutations in the gene for dystrophin
 Becker = reduced abundance and/or size of protein
 Duchenne = severely reduced/no protein present
Polymerase Chain Reaction (PCR) – analysis of nucleic acids for variations
o Makes millions of copies of a specific DNA sequence to visualize it on a gel
o Use the patient template DNA, 2 primers (forward and reverse primer) which are
complementary to the region we want to copy, DNA polymerase, and free nucleotides
o Heat the patient DNA to unwind it, then primers anneal on each strand, cool down the
test tube to a temp where DNA polymerase can work so it can extend the DNA primer
to create new strands. Repeat many times.
o For analysis, run the PCR fragments on a gel to separate based on length
 Must have markers to use as a scale for size comparison
o Pros:
 Can determine variation in DNA size based on length of PCR fragment between
primers
 Detects insertions and deletions
o Cons:
 Must know something about the sequence (confirmatory) bc need to design 2
primers
 Can only easily amplify up to 10kb
o PCR product size = length of primer + length of intervening sequence
o Clinical Ex:
 Huntington’s Disease results from trinucleotide expansions of CAG = longer DNA
length = higher band on the gel
Sanger Sequencing – most common method of DNA sequencing
o Use of dideoxynucleotides (with a hydrogen instead of an OH at the 3’) bc they
terminate DNA synthesis since phosphodiester bond cannot form
o Template strand is added in a test tube with regular nucleotides (dNTP) and dideoxy
(ddNTP) and DNA polymerase. Each ddNTP is tagged with a different color
fluorescence based on the nitrogenous base. Randomly, the DNA polymerase uses
ddNTP instead of dNTP while it is replication, which generates varying lengths of DNA
strands.
o These varying length strands are run through a capillary gel electrophoresis that is read
shortest to longest (5’ to3’) with a laser detector system connected to computerized
analysis that can determine the sequence of the DNA nucleotide by nucleotide.
o The computer-automated high-throughput DNA sequencing generates large amounts
of sequence DNA and has enabled rapid progress of the Human Genome Project
o Pros:
 Can determine every nucleotide in a DNA molecule; can detect any change to
a specific DNA sequence that may or may not impact the DNA length
 Detects silent, missense, nonsense, deletion, or insertion
o Cons:
 Can be expensive
 Only 600-900 nucleotides determined per sequencing reaction
 Requires knowledge of locus of interest in order to design primers (confirmatory)
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Next Generation Sequencing (NGS) – can sequence every nucleotide in DNA sequence
o Allows sequencing with many primers simultaneously
o Take the DNA sample and create DNA fragments that can be embedded onto an
array disk with DNA primers so that each fragment can be sequenced all at the same
time
o Pros:
 Can determine every nucleotide in the exome or genome and detect any
change the sequence
 Detects silent, missense, nonsense, deletion, insertion
o Cons:
 Can be expensive
 Analysis of data is intensive (exploratory)
 We don’t have the proper technology/resources to store that much data
but it is becoming more common
DNA Microarray
o Thousands of spots are arrayed orderly on a chip. Each spot on a microarray contains
DNA with known unique sequences. The precise location and sequence of each spot is
recorded in a computer database. Each spot represents one gene, one sequence, one
gene variant, or one allele
o The patient DNA sample is washed over the microarray. If the DNA sequences are
complementary to any of the known ones, then it will hybridize/stick to that spot and
create a yellow signal that can be analyzed on a computer. Depending on the colors
reflected and read by the computer, it can show loss or gain of DNA
o Pros:
 Very specific
 Can test thousands of sequences at once
 Versatile
 Can look for single nucleotide changes, changes in mRNA levels, changes in
copy number, and at the chromosome level
 Detects silent, missense, nonsense mutations, and variations in noncoding
sequences
o Cons:
 Can be expensive
 Not necessary if the disease and genetic mutation associated with the disease is
known (exploratory)
Test type
Molecule Type of variation
detected detected
Examples of variation
changes detected
confirmatory notes
or exploratory
Western blot
Protein
Variation that
changes protein
size, quantity of
protein, loss of
protein
Nonsense mutation in coding confirmatory
DNA (truncated or no
protein), promoter mutation in
DNA (affects mRNA and
protein)
PCR
DNA
DNA sequence
variation that
increases or
decreases DNA
fragment size
between 2 primers
Insertion (e.g. triplet repeat
expansions), deletion
confirmatory
Requires known
sequence to
design 2 primers
Sanger
sequencing
DNA
Any change to a
specific DNA
sequence (may or
may not impact
DNA length)
Silent, missense, nonsense,
deletion, insertion
confirmatory
Requires
knowledge of
locus of interest
to design primers
Next
generation
sequencing
DNA
Any change to the Silent, missense, nonsense,
deletion, insertion
DNA nucleotide
sequence (genome)
exploratory
Becoming more
common and less
expensive
Microarray
(DNA)
DNA
exploratory
Single DNA
Silent, missense, nonsense
nucleotide change mutations (coding), variation
in noncoding sequences
Requires an
antibody, known
protein, normal
control
Mendelian Inheritance
Mendel’s Laws
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Law of Segregation – sexually reproducing organisms possess genes that occur in pairs and
only one member of the pair gets transmitted to the offspring
o Ex: we have one maternal allele and one paternal allele; in the next generation/within
the gametes, these two alleles will segregate away from each other
o This law is used to generate Punnett squares and as we predict gamete possibilities
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Law of Independent Assortment – the alleles at one locus segregate independently of the
alleles at another locus
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Law of Dominance – in a pair of alleles, one is dominant, and the other is recessive
o The phenotype of a trait is dependent on the relationship of the alleles
Patterns of Inheritance
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Autosomal Dominant – only one copy is needed to manifest a trait
Autosomal Recessive – requires two copies to manifest a trait
Carriers – person is heterozygous for an autosomal recessive trait/disease; are not affected but
can pass it to offspring
X chromosome
o An X chromosome is much larger than the Y, but this is not problematic for males due to
cellular compensation with X inactivation
 = silencing of genes on one of the X chromosomes of an XX individual
 Occurs early in development
 7-10 days after fertilization
 Random
 Which X chromosome inactivated is random from one cell to the next
 = mosaic representation
o Like in female calico cats
 Fixed
 Once inactivated, it stays that way for the entire life of the cell and all of
its daughter cells
 Incomplete
 85% of genes on the X are inactivated; the other 15% is not
 This explains why people with an abnormal number of X chromosomes
have an abnormal phenotype bc there is still expressed genetic info
 Barr body – an inactive X chromosome; appears as a dense, dark-staining spot
at the edge of the nucleus of each somatic female cell
 # of Barr bodies = # of chromosomes – 1
o X-linked Recessive
 Females need two recessive X alleles (homozygotes) OR
 Males need one recessive X alleles (hemizygotes) to manifest the trait
 Clinical Ex: Duchenne muscular dystrophy
 Result of defective gene on the X chromosome that encodes for the
membrane skeletal protein dystrophin
 Clinical Ex: Hemophilia A
 Result of mutation in clotting factor VIII
 Most patients are male, but some females may be manifesting
heterozygotes
Manifesting heterozygote - a female heterozygote that manifests clinical symptoms of
an X-linked recessive disorder
 Occurs bc of the randomness of X inactivation
 = possibility that the majority of the X that is expressed has the mutated
gene
o X-linked Dominant – need one dominant X allele to manifest the trait
 Clinical Ex: Rett Syndrome
 Most likely a non-mendelian mutation; a de novo mutation = new
mutation within the germline
Y-linked Inheritance
o Transmission is exclusively male to male
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Pedigrees
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Family History
o Start with proband/index case (the individual who first brought attention) and record
relevant data (trait, sex, age, age of onset)
o Spouse/partner
o Proceed systematically through parents, grandparents, kids, aunts, uncles
 Ask about ages, date of death, cause of death, miscarriages
o Both sides of the family
o Need at least 3 generations
Recurrence risk – the chance that a condition will recur in a relative of an affected person
Autosomal Dominant
o Vertical pattern of inheritance with multiple generations affected
o Each affected person has one affected parent
o Each child of an affected person has 50% chance of being affected
o Unaffected people have unaffected offspring
o Males and females equally affected
 Bc autosomal so no relation to the sex chromosomes
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Autosomal Recessive
o Horizontal transmission; more than one sibling affected
o Skips a generation; parents and children of affected people are usually affected
o Each subsequent sibling of an affected person has a 25% chance of being affected
o Both sexes equally affected
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X-linked Recessive
o Males are more commonly affected
o No male-to-male transmission bc males get X chromosome from mothers
o Affected males have 100% carrier daughters and 0% affected sons
o Unaffected female carriers transmit the mutated chromosome to 50% of their sons
(affected) and 50% of their daughters (unaffected carriers)
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X-linked Dominant
o Does NOT skip generations
o Females are more commonly affected than males bc they have two X’s
o Affected males have 100% affected daughters and 0% affected sons
 no male-to-male transmission
o Affected females have 50% affected daughters and 50% affected sons
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Y-linked Inheritance
o Does NOT skip generations, unless there is no males
o ONLY male-to-male transmission
o Affected males have 100% affected sons and 0% affected daughters
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Mitochondrial Inheritance
o ALL mitochondria are inherited from MOM
o Mitochondria all have their own circular DNA; small amount but comparatively high
mutation rate bc close proximity to ATP creation and ROS
Most mitochondrial disease lead to neurological diseases such as Leber
hereditary optic neuropathy
Affected females have close to 100% affected offspring
Affected males have 0% affected offspring
Both sexes are equally affected
Heteroplasmy – the presence of more than one type of mitochondrial DNA in a single
cell
 Could result in variable expression of the disease as well incomplete penetrance
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Probability + Population Genetics
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Genotype frequency/Incidence: divide the number of each genotype by the total number of
samples
Allelic frequency: divide the number of alleles by the total number of alleles
Hardy-Weinberg Principle – in a large random mating population, there is a non-changing
relationship
o Allelic frequency: p + q = 1
o Genotype frequency: p2 + 2pq + q2 = 1
o p = Dominant
o q = Recessive
o pq = Heterozygous Carriers
Complications to Mendelian Patterns of Inheritance
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Incomplete dominance/Partial dominance/Haploinsufficiency
o Phenotype in the heterozygote carrier is different from that seen in both homozygous
genotypes and its severity is intermediate
o Neither allele is dominant
o Clinical Ex: sickle cell trait = one affected, one unaffected = no anemia but still sicked
shape
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Codominance/Co-dominant Alleles
o Expression of each allele can be detected even in presence of the other
o Clinical Ex: ABO blood groups
New mutations
o Typical of autosomal dominant disorder that suddenly appears in a family
o Parents are normal
o Can arise in germ cell of the parent (germline mosaic) or early on during embryogenesis of
the affected individual
o Clinical Ex: Achondroplasia
o Germline/gonadal mosaicism – the presence of a new mutation in a germline cell of an
unaffected individual
 There is a collection of cells that have new mutations in it. If it occurs early in the
germline development, every cell progressing from it will be mutated. But the
neighboring germline cells may not be mutated.
 Multiple siblings can be affected depending on when in the germline development
it occurred
 May look like a recessive trait even if dominant trait
Penetrance
o The probability that an individual with a given genotype is affected with the disease
o Assumed that penetrance is 100% unless otherwise stated
o Risk of seeing the phenotype trait = (recurrence risk of genotype) x (penetrance)
o Clinical Ex: retinoblastoma
 10% of pts with the disease allele do not have the phenotype
 So penetrance is 90%
o Age-dependent penetrance – age of onset is generally AFTER reproductive choices are
made
 Reduces natural selection
 Clinical Ex: Huntington Disease, Familial Alzheimer’s Disease, Cancers
o Gender-dependent penetrance
 Clinical Ex: females more common for breast cancer
Variable Expression – varying degrees of manifestation of the disease; relates to severity of
disease
o Can be due to the environment and/or allelic heterogeneity
Allelic Heterogeneity – the production of identical/similar phenotypes by different alleles within
the same locus
o Different allele mutations, same disease (phenotype)
o Norm for Mendelian disorders
o Clinical Ex: Cystic Fibrosis can over 1500 different mutations in CFTR gene
o Leads to varying levels of severity based on the mutation
 Class 1 = most severe
 Class 6 = least severe
Locus Heterogeneity – single disease caused by mutations in different loci
o Different loci/genes, same disease
o Clinical Ex: osteogenesis imperfecta
 Ineffective type 1 collagen is produced through 3 different proteins
Pleiotropy – when a single mutation has affects on multiple parts of the body
o Clinical Ex: Marfan Syndrome – ocular, cardio, and skeletal
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Consanguinity – mating between 2 individuals with at least one ancestor in common; no more
remote than great-grandparent
o Increase the chance of inheriting a recessive trait
o Marked by double lines
Non-Mendelian Inheritance
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Mitochondrial Inheritance
o “three parents” technique – potential genetic treatment for mitochondrial disease
 Egg donor with healthy mitochondrial DNA. Parents’ embryo with unhealth
mitochondria. Donor’s pronuclei is removed and replaced with the parent
pronuclei (with all genomic DNA) via IVF into the healthy mitochondria donor
embryo = parent pronuclei inside healthy mitochondria embryo
Genetic Imprinting – silencing of genes via epigenetic modification, specifically methylation
which blocks transcription factors from binding to it; ~200 genes in the genome are subject to
imprinting naturally
o Sex-specific gene silencing; mutually exclusive male vs female
o Consistent in all somatic cells permanently
o Imprint pattern is ‘reset’ in the germline/gametes of the next generation
 both father’s and mother’s imprint passed onto the child’s somatic cells.
Depending on if the offspring is male or female, then the gamete cells that the
offspring produces are reimprinted to male-only (sperm) or female-only (eggs)
depending on their sex
o Clinical Ex: Prader-Willi Syndrome (if deletion in dad’s PWS region on chromosome 15)
and Angelman Syndrome (if deletion in mom’s AS region on chromosome 15)
 The deletion = lack of expression = disease; Beckwith-Wiedemann Syndrome (loss
of maternal or paternal imprinting = double gene expression = overgrowth of
organs and propensity for cancer)
Anticipation – earlier and/or more severe disease onset with successive generations
o Suggest that repeat expansion can be the cause; more with each generation
o Clinical Ex: triplet repeats, Huntington’s Disease, myotonic dystrophy, Fragile X
Syndrome
 Fragile X = only the maternal copies are expanded
Cytogenetics






Cytogenetics – the study of chromosomes + related disease states caused by abnormal
chromosome number and/or structure
When do we study chromosomes?
o Unexplained intellectual disabilities, multisystem anomalies, neonatal death/stillborn
infant, ambiguous genitalia, hypogonadism/amenorrhea, infertility, multiple
miscarriages
Mitosis – DNA of a 2n cell replicate to create a 2 x 2n cell that divides to produce 2 identical
daughter cells that are each 2n
Sister chromatids – replicated DNA copies
Meiosis – produces 4 genetically different haploid gametes
Meiotic crossover – occurs during Prophase 1; DNA chromosomes already replicated, resulting in
sister chromatids
o ensures proper segregation of homologous chromosomes during meiosis and creates
genetic diversity



Karyogram – the visual representation of chromosomes based on length and banding patterns;
sex chromosomes at the bottom right
Karyotype – the nomenclature/reading and analysis of chromosomes, including the number and
types of chromosomes
o (# of chromosomes), (sex chromosomes), (additional info;
abnormality(chromosome#)(arm band))
o Ex: 46, XY, dup(5)(p14p15.3) represents 46 chromosomes, male, duplication on
chromosome 5 on the short arm from band 14 to 15.3
o
Centromere Structure Naming
o Metacentric – centromere in middle
o Submetacentric – upper part
o Acrocentric – tiny centromere bc there is not enough genetic info; only satellite DNA
above centromere
Numerical Abnormalities


Polyploid – complete extra set of chromosomes
o Triploidy – three full sets of chromosomes; (69, XXX)
 Incompatible with life
 3 ways to produce:
 Dispermy
 Meiotic failure of 2n sperm
 Meiotic failure of 2n egg
Aneuploidy – containing an additional or missing individual chromosomes; not a multiple of 23
o A = an = one individual more/less
o Monosomy – presence of only one copy of chromosome in a diploid cell
 Turner Syndrome: 45, X
o Trisomy – three copies of a chromosome in a diploid cell
 Down Syndrome: 47, XX or XY, +21
 Edwards Syndrome: 47, XX or XY, +18
 Patau Syndrome: 47, XX or XY, +13
 Klinefelter Syndrome: 47, XXY
 Triplo-X: 47, XXX
 47, XYY
o Occurs bc nondisjunction – chromosomes or chromatids failed to segregate properly

 Normally occurs during meiosis 1 when there is not crossover
Maternal Age Effect – related to the idea that the oocytes don’t complete meiosis until they are
released for ovulation; as the oocytes get older, they can start to break down of mechanisms or
have a higher risk of nondisjunction
Structural Abnormalities


Unbalanced – rearrangement causes a loss or gain of genetic material; change in DNA
content
o Ex: deletion, duplication, isochromosomes
o Deletion – when a chromosome breaks and some genetic material is lost
 Terminal – deletion on chromosome ends/tips; one break on one chromosome
 46, XY, del(4)(p16.3)
 Interstitial/Intercalary – internal deletion in the middle of chromosome; two
breaks on one chromosome
 46, XY, del(5)(q13q33)
 Macrodeletion – larger deletion that can be visualized with standard karyotype
staining
 46, XX or XY, del(5p)
 Cri Du Chat; Wolf-Hirschhorn
 Microdeletion – smaller deletion that are not visualized with standard karyotype
 46, XX, del(7)(q1)
 Williams Syndrome; WAGR
 Ring chromosomes – results from deletion at both ends/telomeres; the ends fuse
together; can only be tolerated by X chromosome
 46, X, r(X)(p22.3q28)
o Duplication – when part of a chromosome is copied/duplicated abnormally = extra
genetic material
 46, XX, dup(10)(q22q25)
o Isochromosome – divides along axis perpendicular to normal axis of division; divides
horizontally
 2 short arms or 2 long arms fuse together and passed onto zygote
 X chromosomes only tolerate this abnormality
Balanced – rearrangement does not produce a gain or loss of genetic material; NO DNA
content change
o Ex: uniparental disomy; inversion; translocation
o Uniparental disomy – patient has normal amount of DNA, but both alleles are from ONE
parent
 Occurs from double non-disjunction or from one non-disjunction  trisomy
zygote and chromosome loss
 Bad if parent has recessive disorder, then it will present in offspring
o Inversion – inverted/reversed segments
 Paracentric – doesn’t include centromere; 2 breaks on one arm
 Pericentric – surrounds centromere; break on long and short arms
 Problems occur in meiosis with gametes
 Crossing over in pretzel/looped shape = improper = chromosomes with
deletion and duplication
 No clinical features in parent but will have difficulty reproducing
o Translocation – a piece of one chromosome breaks off and attaches to another
Reciprocal – breaks occur in 2 chromosomes and the material is mutually
exchanged
 46, XY, t(4;8)(p23;q31)
 Problematic for offspring; possible problems with reproduction
o Possible normal, balanced carrier, or partial trisomy + partial
monosomy
 Robertsonian – where short arms are lost and long arms are fused
 45, XY, der(13;14)(p10;p10)
o Must be p short arm notation by definition
 Only happens between acrocentric chromosomes (bc no coding regions
above but still loss of chromosome = 45)
 Problematic for offspring; leads to possible trisomy or monosomy
Complex rearrangements – spontaneous rearrangement in somatic cells; mostly in
cancers

o
Chromosome Visualization
Staining Techniques

DNA binding
o Giemsa – G-banding based on polarity of chromosomes; most common; purple dye
o Reverse – R-banding; helpful to visualize tips/ends of chromosomes
o Create maps of staining bands based on amount of pyrimidine or purine concentration
o Detects large changes in chromosome structure
 Macrodeletions, macroinsertions, polyploidy, aneuploidy, some translocations
o Exploratory AND confirmatory
Non-Staining Techniques

Hybridization-based
o FISH (fluorescence in situ hybridization)
 4 types:
 Whole chromosome
o Spectral karyotype/SKY – detection of translocations + complex
rearrangements as every chromosome is painted a different color
 Detects large changes in chromosome structure =
macrodeletions, macroinsertions, polyploidy, aneuploidy,
and all balanced translocations
 Exploratory
 Single copy
o Detect gain or loss of DNA locus; microdeletions + microinsertions
o Confirmatory
 Centromeric
o Used as a control to determine where a certain chromosome is
o Does NOT detect variations; used to identify instead
o Confirmatory
 Telomeric
o Interested in ends of the chromosome; detects loss/gain of
telomeres; chromosome fusions
o Exploratory
o
o
o
CGH (comparative genomic hybridization)
 A specialized microarray to detect large chromosomal changes (deletions,
duplications, unbalanced translocations)
 Explorative
Advantages: greater sensitivity than staining techniques; more exact visualization
 Stick to target segments based on sequence complementarity
Disadvantages: more challenging technically; more expensive
Test type
Molecule
detected
Type of
change
Examples of
variation changes
detected
Confirmation
al or
exploratory
notes
Microarray
(CGH)
DNA
Large changes
impacting
chromosomes
Unbalanced
translocations,
insertions, deletions,
duplications
exploratory
Not able to
detect balanced
translocations,
single nucleotide
changes
Karyogram
(staining)
DNA/chro
mosomes
Large changes
in chromosome
structure
Macro deletions,
macro insertions,
polyploidy,
aneuploidy, some
translocations
Exploratory
and
confirmatory
FISH (whole
chromosom
e paint
probe; SKY)
DNA/chro
mosome
Large changes
in chromosome
structure
Same as G banding
karyogram and all
balanced
translocations
exploratory
FISH
(telomere
probe)
DNA/chro
mosomes
Gain or loss of
telomere
sequence
Loss of telomeres;
chromosome fusions
exploratory
FISH (single
copy probe)
DNA/chro
mosomes
Gain or loss of
DNA locus
Microdeletions,
microinsertions
confirmatory
FISH
(centromere
probe)
DNA/chro
mosomes
N/A
No variation
detected, but used
with single copy
probe to identify a
chromosome of
interest
confirmatory
Must have
information of
the locus to
design probe
Screening for Genetic Disorders


Genetic screening – performed for a particular condition in individuals, groups, or populations
without family history of the condition; explorative
Genetic testing – performed for a particular condition where an individual is suspected of
being at an increased risk bc of their family history or result of a genetic screening; mostly
confirmatory
Principles of Screening









Condition should be serious
Condition should be “relatively common”
Acceptable + effective treatment available
Easy to perform screening tool
Relatively inexpensive
Test should be valid + reliable
Resources for diagnostics testing + subsequent treatment should be available for the follow-up
Communication strategy should be in place
Screen should be inclusive and then confirmed (usually be diagnostic/genetic testing)
Tiered Testing


Diagnostic tests are used to confirm the results of screening tests.
o If a person is positive on a screening test and negative on the specific diagnostic test,
then the doctor must reassure them that they do not have the disease.
Tiered testing – start broad and inclusive, then confirm.
o Ex: For HIV: start with ELISA screen, then test with a Western Blot for HIV viral proteins
o Results of a Typical Screen:


The cut-off point for screening positive for carrier status is to the RIGHT and
negative for carrier status is to the LEFT of the 95th percentile
Screening Tool Characteristics

Sensitivity – refers to how many cases with a disease/disease allele score positive with the
screening tool.
o Very sensitive screen = a fair number of false-positive results but almost no true positives
will be missed
o Tools with a high sensitivity are often used to screen for disease
 Screens cast a wide net in order to pick up all cases of a disease and not miss
anyone, but that often leads to accidental positive results in people who don’t
have the disease
o
o
o

The shaded region refers to those who will have a positive result from the screen
100% sensitive is NOT very useful bc there are too many false positives that come with
all of the true positives. Cutoff value is too high.
Specificity – refers to individuals without the disease that have a negative result; reflects how
accurately diagnosed a particular disease is without giving false-positives/how well it correctly
identifies those WITHOUT the disease
o
o
o


The shaded region displays all those without the disease who received a negative result
100% specific is NOT very useful bc there are too many false negatives and people with
milder degrees of the disease will be missed. Cutoff value is too low.
False positive result – positive screen result for a person who does not have the disease (yellow
shaded)
False negative result – negative screen result for a person who does have the disease (green
shaded)
o








Positive predictive value – fraction of patients with positive results are affected
o Demonstrates the screen’s ability to accurately screen for the disease it is being used to
detect
Negative predictive value – fraction of patients who are given a negative result and are not
affected

Sensitivity: fraction of people with the target disease who have a positive result = a/(a+c)
Specificity: fraction of people without the target disease who have a negative result = d/(b+d)
Positive Predictive Value: fraction of people with a positive result who have the target disease
= a/(a+b)
Negative Predictive Value: fraction of people with a negative result who do not have the
target disease = d/(c+d)
Sensitivity + Specificity is Straight Up + Down/Vertical analysis
Predictive Values are Horizontal analysis
Types of Screening

Screening is non-invasive (ultrasound, blood, urine, sweat, spit)
Prenatal Screens




Ultrasound – 11.5-13.5 wks
o Nuchal translucency – visible large growth along back = likely chance of Down
Syndrome
o Also visible CNS defects, chest, abdomen, pelvis, skeletal system, craniofacial (cleft lip
or palate)
Human Chorionic Gonadotropin (hCG) – first trimester
o Increased levels in first trimester of pregnancies affected with fetal Down Syndrome
Pregnancy-Associated Plasma Protein A (PAPP-A) – first trimester
o Decreased levels in first trimester of pregnancies affected with fetal Down Syndrome
PAPP-A + hCG + nuchal translucency measurement + maternal age = risk of fetus having
various trisomies
o


Alpha-Fetoprotein (AFP) – 2nd trimester
o Decreased in pregnancies affected with fetal Down Syndrome
o Increased in pregnancies with fetal neural tube defects (ex: spina bifida)
Fetal Cell Free DNA Sequencing – as early as 10wks
o Relatively new method in which non-invasive sample of cell-free fetal DNA (cffDNA) is
taken from mother’s blood sample as early as 10 weeks
 cffDNA is isolated, PCR amplified, and sequenced with Next Generation
Sequencing for trisomies, sex chromosomes, and microdeletions
o sometimes recommended to be followed-up with biochemical screen or to be used
with high-risk populations only
Newborn Screens

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
Special case that, depending on the disorder and the screening method, may identify
carriers, presymptomatic individuals, or affected neonates.
Population-based screening in which ALL newborns are screened unlike selective screenings
WHO & NAS Criteria for Newborn Screens
o Reliable, repeatable, accurate, sensitive + specific, amenable to automation, clinically
significant disorder, treatable (not necessarily curable), relatively high frequency, cost
effective/beneficial
35 screens on the National Recommended Uniform Screening Panel (RUSP)
o Each state may include additional screens
Baby’s First Test raises awareness of newborn screening and improves understanding +
informed decision-making capacity of parents. It provides a central linkage location for
access to informational resources and data
Newborn Screening Quality Assurance Program (NSQAP) assures the highest standards of
performance of newborn screening alongside the CDC and local public health laboratories
Ex:
o PKU Punchout Card
 Blood spot from heel prick on newborn day 2 placed on card that is mailed off
to lab testing
 PKU was the first disease that was
screened in newborns in 1978. PKU
leads to a defective enzyme,
leading to a buildup of
phenylalanine = toxicity = affects
brain development. Treatment is
dietary restrictions, especially of
protein.
o Congenital Hypothyroidism
 Screening for TSH levels and puffy eyelids, macroglossia, and umbilical hernia
 Thyroid gland fails to develop or function. Untreated = lower IQ and abnormal
growth from permanent brain damage. Tx of hormone replacement.
o Glutaric Acidemia Type 1
 Body cannot breakdown amino acids = buildup of glutaric acid = severe sudden
onset of dystonia; early intervention with diet, glucose, and co-factors through
specific formula
Take Home: newborn screening for diseases in which clinical manifestations include missing a
normal product (enzyme, hormone, etc); intervention can prevent progression; oftentimes
treatment is dietary restriction; often have different rates in different populations
Adult Screens




Heterozygous Carrier Screens
o Target population are those known to be at risk
o Screening panels often include most common variants
o Disease screened for are typically autosomal recessive for which prenatal diagnosis
and genetic counseling are available and feasible
o Non-invasive (saliva)
o Used for family planning. # of conditions screened grows each year
o Negative Screen Results determines
 Residual Risk – risk that you may still have the disease and the mutation was not
part of the screening/was not on the panel
 Reproductive Risk – risk that the person’s offspring will have the disease
 Math and assumptions are made (ex: with ethnicity) to determine risk
o Positive Screen Results = partner subsequently tested
Ex:
o Tay-Sachs Disease
 AR lysosomal storage disorder; accumulation of metabolic intermediates in
neurons
 Especially common among Ashkenazi Jewish people (1/30 heterozygous
frequency)
 With availability of screens (for buildup of metabolite), # of Tay-Sachs births has
decreased by 90%
Some diseases may be screened specifically higher for certain populations
Hereditary Cancer Screens
o Typically for high-risk individuals: those diagnosed with cancer; 1st degree relative; male
breast cancer in family
Genetic Testing




No single definition
o Analysis of human DNA, RNA, chromosomes, proteins, or certain metabolites in order to
detect heritable disease-related genotypes, mutations, phenotypes, or karyotypes for
clinical purposes
o Can be used for health and non-health purposes, and to detect non-heritable changes
(ex: tumor typing, drug selection, paternity testing, forensics)
Genetic Testing Registry provides a central location for voluntary submission of genetic test
information by providers. Goal to advance public health and research into genetic basis of
health and disease. Provided by NIH, intended for public use and for healthcare providers
Regulation
o Centers for Medicare + Medicaid Services regulate clinical labs by creating education
requirements for technicians, quality control of lab processes, and proficiency testing
o FDA regulates test kits ordered by labs
o FTC regulates false + misleading advertising
Types
o Carrier Identification – genetic tests used by couples whose families have a history of
recessive genetic disorders and who are considering having children
 Also done by populations at a particularly high risk; but this would be considered
a SCREEN amongst those populations



o
Targeted to an individual based on family hx, results of a screen, or ethnic
background
Molecular Techniques:
 VNTR + STR polymorphisms (PCR)
 Microarrays
 Sequencing (Sanger, Next Gen)
 Comparative Genome Hybridization
Case Study Example:
 Angela and husband Jim come to you for genetic testing + counseling,
bc they are thinking about starting a family. Angela has a sister who died
of complications from CF when she was 18, and Angela is very worried
that her children will also have CF. Angela is a non-Hispanic U.S.
Caucasian, Jim is African American, and neither is Jewish.
 From examining this pedigree, what is the probability that Angela carries
the CF mutation? 2/3 bc parents are both carriers = normal chance of ½
but we know she is not affected so 2/3
 The probability that Jim is carrying a mutation, based on population data
is 1/65.
 What is the probability that they have a child with CF?
(2/3)(1/2)(1/65)(1/2) = 2/780 = 1/390 = .00256 = .26%
 Angela and Jim participate in the 165 variant panel. Angela is confirmed
to be carrying a pathogenic variant of CFTR. Jim is negative for the
variants tested in the panel.
 What is the chance that he carries a less common CF allele not included
in the panel? Residual risk = 100-78 = 22%
 What is the chance that Angela and Jim will have a child with CF?
(1/2)(1)(.22)(1/65)(1/2) = .08%
 Almost a 3x decrease from calculated risk before testing; reduces anxiety
for the family
Preimplantation Genetic Diagnosis (PGD) – test on embryos
 Used when offspring is at risk for a diagnostic genetic disorder
 Genetic test which detects the presence of alleles for specific diseases within
embryos or if the cells in an embryo have the correct number of chromosomes
 Occurs during IVF
 Around days 3-5 of embryonic development, a cell is removed for biopsy
for mutated alleles + # of chromosomes. Multiple samples are taken from
different embryos and then implant unaffected embryos. V expensive.
Select Mendelian Disorders that PGD is offered for monogenic or chromosomal
disorders such as thalassemia, cystic fibrosis, Huntington disease, sickle cell
anemia, Tay Sachs disease, Fragile X Syndrome, Marfan Syndrome, etc.
Prenatal Diagnosis – test on fetus
 Performed when maternal age >35y/o; previous child w/ autosomal trisomy;
parent has chromosomal translocation; spouse or previous child with neural tube
defect; pregnancy at risk for diagnosable disorder; abnormal screening results
 Chorionic Villus Sampling (CVS) – 8-12wks
 Sample taken from placental tissue at around 8-12 weeks; risk of a
spontaneous loss from the procedure is ~1/100
 Procedure: suction tube enters cervix, removes some cells, cells get spun
down + run through biochemical tests; karyotyped; results in about a day
 Problem 1-2% of the time with confined placental mosaicism = tissues that
form the developing embryo (placenta + fetus) are a mosaic and have
different genotypes. Occurs from a new mutation. Therefore the sample
taken from the placenta may NOT be representative of the fetal DNA.
 Amniocentesis – 14-18wks
 Amniotic sample taken with a needle inserted through the abdomen and
placenta. 50cc fluid removed. Fetus sloughs off many developing cells.
Fetal cells in fluid spun down. Not as much sample as CVS so must
CULTURE the cells for a few weeks before karyotyping and getting results.
 Risk for spontaneous loss from procedure is 1/200
Presymptomatic/Predisposition Testing – for predicting late-onset disorders (ex:
Huntington’s Disease, Adult Polycystic Hemochromatosis, Autosomal Dominant Breast
Cancer)
 Huntington’s Case Study Example:
 What kind of genetic disorder is HD? Autosomal dominant
 Are there reliable genetic tests available? Molecular mechanism: triplet
repeat expansion of CAG. Use PCR testing.
 What testing method would be most appropriate for HD? Use PCR testing.
 Lane 1: size marker; Lanes 2 + 4: David; Lane
10: negative control.
 How many repeats does
David here? 17 + 42
 What is David’s
diagnosis? Since he has
one gene over 40 (42), and
HD is AD, then he is
affected and has a 50%
chance of transmission.

o
o
o
Confirmational Testing – for clinical diagnosis; to confirm a positive result from a genetic
screen
 Case Study Example:
 Emily born with congenital heart
defect and submucosal cleft
palate. She had a seizure at 2
months old. The pediatrician
suspected DiGeorge Syndrome
(caused by microdeletion of Chr.
22). A standard karyotype was
performed.
Do not notice anything obvious bc DiGeorge’s is a MICROdeletion and
undetectable. Follow up test with FISH single copy gene probe.
o Green = Chromosome 22
o Pink = q11.2 band (deleted in 90% of DiGeorge’s Syndrome
 FISH interpreted: There is one deletion of the 11.2 band in the long arm of
chromosome 22 based on the presence of only 1 pink fluorescent band
 Karyotype: 46, XX, del(22)(q11.2)
Comparative Genomic Hybridization (CGH)
 Used if there is a specific region where we want to explore unknown
clinical manifestations and try to identify whether or not there is a
cytogenetic change.
 Explores the entire genome, mixing patient sample with certain color
fluorescence. Mixed with control DNA with different color fluorescence.
Wash them both over a microarray and notice where the fluorescence is
at an unequal ratio.
o If fluorescence of only patient DNA = DNA GAIN
o If fluorescence of only control DNA = DNA LOSS


o
Identification of genetic information belonging to a specific individual; “identify” bc
need to have a sample to compare to
 DNA Fingerprinting
 Paternity Test
 Uses short tandem repeat polymorphisms (STRP) at different loci (~13-16
loci)
o Each of the loci have a different value of confidence for the
relationship index per match based on the variability options of the
allele itself in the population.
If an allele has only 3 versions then the chances of a match
would have a lower relationship index compared to if the
allele had 20 variations and there was a match.
 3+ negatives EXCLUDES the father
 If combined parentage index (CPI) >100 points or probability of paternity
>99% = biological father in court of law
Direct-to-Consumer Genetic Testing
o Direct sale of testing services and provision of test results to consumers without health
care provider intermediary
o Pros:
 Easier access to genetic information
 Outside medical system
 Personal control
 Motivation to make positive behavior or lifestyle changes
 Knowledge + insight
o Cons:
 Unregulated
 Privacy concern (data
accuracy/validity of test
sold)
 Laboratory quality
 Surreptitious/secretive
 Lack of counseling
testing
 Misinterpretation
 Consequence for other
 Inappropriate test
family members
selection
o Should NOT be considered a diagnosis
o False positives can lead to unnecessary medical treatment and other ethical issues
o Ex: 23andMe Saliva Test
 “health assessment” along with ancestry without health claims of diagnoses. FDA
shut them down before. New language is “risk report” and “associated with” and
“reports do not replace visits to a healthcare professional.”
 Have susceptibility, carrier status, and wellness output along with ancestry and
traits


Multifactorial Inheritance





NOT “mendelian” so not one gene = one trait = one disease
Ex: HTN, Alzheimer, Cancer, Infectious Disease, Osteoporosis, Cirrhosis, Psoriasis, Glaucoma,
Asthma, CVD, Schizophrenia, Bipolar Disease, Depression
Polygenic – MANY genes = one trait
Genes + Environment = Disease
o Ex: risk of lung cancer associated with polymorphisms in GST-1 and increased with
smoking; cirrhosis associated with polymorphisms in epoxide hydrolase and risk
increased with alcohol
Multifactorial – many genes AND environment = one trait
o Principles:
 Large numbers of isolated cases; relatively common but not clustered within
families; clumped across geography
 Increased risk to relatives BUT declines exponentially with decreasing kinship to
affected proband
 No recognizable pattern of inheritance
 Many traits are quantitative and fit under a bell-shaped population distribution
Quantitative trait – most are multifactorial and are measured on a
continuous numerical scale
o Ex: height, BP
o Distribution of trait is somewhat proportional to the number of
genes that make up that trait
 Multifactorial traits that do NOT follow a bell-shaped distribution are either
present or absent (like single-gene disorders) but do not follow the same
inheritance patterns of single-gene disorders. Instead, they have a threshold of
liability
 Part of the model of human disease in which it takes multiple “hits” before
a cell, tissue, or person manifests a disease.
o “hits” can be genetic or environmental
 Sex-influenced traits – multifactorial traits in which each sex has a differing
threshold of liability, and this is unexplainable through other gene factors
o NOT to be confused with sex-linked (single-gene disorders that are
x- or y- linked) or sex-limited traits (in which both sexes have the
genes but only one sex manifests the trait bc of physiological
limitation)
 Susceptibility Alleles of multifactorial traits have low penetrance
 They require multiple factors so genes alone are not enough to lead to
the trait. Other hits are needed for penetrance.
 Susceptibility Alleles of multifactorial traits have high population frequencies
 Bc of low penetrance, there is no selectivity against them = able to spread
around the population
Recurrence Risk – the chance that a condition will recur in a relative of the affected person
o For multifactorial traits,
 Determined empirically (with large sets of observable data)
 Higher if >1 family member affected
 Higher if expression of disease in proband is more severe (especially with
bilateral traits)
 In sex-influenced traits, higher if the proband is of the less commonly affected
sex
 Ex: pyloric stenosis is sex-influenced for MALES. More males in the
population have it and they have a lower threshold of liability.
o If FEMALES have the disease, then their family members have a
HIGHER recurrence risk (comparatively to the recurrence risk if a
male had it)
 In order for a female to have it, she had to have a relatively
high number of hits to manifest pyloric stenosis. If we
consider their family, with which she shares genes and
environment, then those family members most likely
experience a similar number of hits, which would put their
siblings (male and female) at a higher risk.
 DECREASES in more REMOTE relatives
 Can VARY from one POPULATION to another
 The more data we have, the better we can predict the recurrence risks
o Take Home: recurrence risks cannot be determined as simply as Mendelian disorders;
many factors influence them in multifactorial disorders; they MUST be determined
empirically with LOTSSS of data and algorithms
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Twin Studies
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Monozygotic – twins share 100% of alleles
o Different phenotypes may still occur due to spontaneous mutations to DNA,
environmental factors, and x-inactivation
Dizygotic – twins share 50% of alleles
Concordance – when twins share a trait
Discordance – when twins do not share a trait
Heritability – a measure of the genetic component in a complex disease; the % of population
variation in a trait that is due to genotypic differences
o Falconer’s Formula: h = 2(CMZ – CDZ)
o HIGHER heritability = more of the total variation of a trait is due to genetic variation (for
that given population in a specific environment)
o LOWER heritability = more likely higher environmental component to trait
o Ex: Human Height heritability value = 0.65 = 65% of overall variation in height is due to
genotypic differences between individuals within that specific given population
o Limitations:
 Does NOT suggest what/which genes determine the traits
 Measured only in populations and has limited application to individuals
 Requires controlled environments and CANNOT be applied to evaluate
differences between populations
 Changes in environmental factors can affect heritability
Adoption Studies
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Studies on 1) identical twins raised apart; 2) children of affected parents raised by unaffected
parents
o Ex: Children born to and raised by parents without disease - have only 1% risk of disease.
Children born to parents with schizophrenia but then raised by unaffected parents have
an 8 - 10% risk of disease. Indicates strong genetic factor in schizophrenia
Limitations:
o Different environments cannot be controlled
 Most likely overlapping similarities in environments such as socioeconomic status
to afford adoption
 Selectivity of parents for what type of child they want
 Monozygotic twins share the same environment for the first 9 months
o Small sample set
o Ethical issues
Common Disease Examples

Stroke
o A. Single-gene disorders associated with stroke
 Sickle cell disease - Hbs (autosomal recessive)
 MELSE: Mitochondrial encephalomyopathy, lactic acidosis and stroke-like
episodes - MELSE (mtND1, mtND5, mtTH, mtTL1, and mtTV)
 CADASIL: cerebral autosomal dominant arteriopathy with subcortical infarcts;
NOTCH3 (autosomal dominant)
o B. Single gene + environment
 Factor V Leiden allele + estrogen
o C. Multifactorial
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 Genetic variants, smoking, hypertension, obesity, atherosclerosis, diabetes
Alzheimer’s Disease
o Affects ~10% of the population > 65 years; ~ 40% of the population > 85 years
o Several-fold increase risk for people with a 1st degree affected relative. Heritability is
~0.80; risk factor is APOE e4 allele
o 3 - 5% of Alzheimer’s cases occur < 65 (early onset)
 these are more likely to be autosomal dominant inheritance, and have
mutations in PS1, PS2, APP
o Protein in brain is normally cleaved at a very specific point in order for the APP protein
to have regular function. With Alzheimer’s, there is inappropriate cleavage of the APP
protein in the brain, which leads to buildup of inappropriate factors that form betaamyloid plaques in the brain. Mutations in PS1 and PS2 increase cleavage activity of
beta and gama-secretase cleaving enzymes which cleave at different points than the
normal alpha-secretase
Heart Disease
o Family history (how many, sex, age, known alleles)
o Genetic determinants of lipoprotein levels
o Genetic determinants of cardiomyopathy
o Long QT Syndrome
Diabetes
o Type 1
 Recurrence risk for siblings is 1-6% (vs. 0.5% in general population)
 Heritability = ~0.80
 Genetic determinants of Type I diabetes: HLA class II alleles DR3, DR;
insulin; NOD, CTLA4, PTPN22
o Type 2
 Recurrence risk for siblings is 15-40%
 Heritability = ~0.60
 Genetic determinants: TCF7L2, PPARG, KCNJ-11
Case Study
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A 50-year-old male Caucasian patient is concerned about his risk of heart attack. His father
died at the age of 60 from an MI. The prevalence of MI in males >> females.

How would you counsel this patient? Although prevalence is higher in males, the heritability is
fairly low suggesting that environmental and lifestyle choices are more influential in risk for MI
compared to genetic.
What concern would you have (if any) if the patient were female, and her mother and
experienced an MI? Would you counsel her differently? There is a genetic factor, but lifestyle
and environmental factors are still very significant because that is what the patient has control
of. May suggest some additional counseling or referral to a cardiologist to make sure that it is
being kept track of/monitored. Counseling very similar to the male patient but acknowledge
that there is an increased heritability which means it is even that much more important to
control and be mindful of environmental/lifestyle factors such as nutrition and activity.
Cancer Genetics
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Cancer is
o Old
o Common – 1/5 deaths; 2nd most common cause of death in US; 39.2% of people will be
diagnosed with cancer during their lifetimes
o Influenced by the environment
 Smoking, carcinogens, sunlight, asbestos
o Genetic
 Clonal Origin – originated from a common ancestral cell that accumulated
numerous specific driver mutations; (cancer cells often do become
heterogenous and deviate genetically due to mutations)
 Driver Mutations
o Give tumor cells growth advantage
o Total number that occur in any particular cancer between 2-8
 Passenger Mutations
o NO direct contribution to the cancer phenotype
o Acquired OVER TIME possibly from high levels of DNA damage +
genomic instability
o Multifactorial
o A multi-step process as cells mutate and become a tumor then malignant
o Take home: Even in cancers that have a strong environmental component (and low
heritability), the end result is gene mutation or dysregulation in order to get to that
phenotype of cancer
Definitions:
o Cancer – uncontrolled growth
o Carcinogenesis – cancer development
o Neoplasm – “new formation” (growth)
o Benign – does NOT invade surrounding tissue
o Malignant – tumor that is capable of invading (metastasizing) surrounding tissues.
Capabilities:
o Cancer cells acquire some or all of these traits to allow for it to grow uncontrollably;
sustaining proliferative signaling (cancer cells need an initiation to grow but can
continue on without that signal); evading growth suppressors; activating invasion +
metastasis; enabling replicative immortality (telomerases); inducing angiogenesis
(initiation of blood vessel growth for nutrient transport); resisting cell death; deregulating
cellular energetics; avoiding immune destruction (after some time, cancer cells don’t
look like regular cells and should be recognized as foreign but they have adapted to
block the immune system); tumor-promoting inflammation (this leads to a more ideal
environment for proliferation and growth advantage of the cancer cells); genome
instability + mutation
Classifications:
o Tissue of origin; ex: carcinoma = epithelial cell; sarcoma = connective tissue; lymphoma
= lymphatic tissue; leukemia = hematopoietic organs
o Stage – description of how far cancer has spread and if it has invaded other organs
o Grade – refers to how differentiated the cells look; measure of anaplasia
(dedifferentiation)
Cancer-Related Genes
o Oncogenes – genes promote growth
 Normal functions of proto-oncogenes:
o
 Growth factors + receptors
 Signal transduction
 Transcription factors
 When ONE allele is mutated, it acts in a dominant fashion at the cellular level to
convert proto-oncogenes  oncogenes
 Results in gain-of-function
 Ex: RAS pathway (normally: proto-oncogene expressed in embryonic
development to help with receptor tyrosine kinase activation with growth
factor to intracellular signaling cascade then transcription factor; mutant
oncogene: even without signal/growth factors, the tyrosine kinase
receptor stays activated or the oncogene turns itself on = inappropriate
intracellular signaling cascade = too much transcription of various genes =
over-proliferation of growth factors
 Identify Oncogenes Methods
 Retroviral insertions in model systems
o Retroviruses can cause cancer by inserting next to and increasing
the expression of cellular oncogenes. Tool used to identify
oncogenes in model systems then applied to homologs in humans.
o We can determine which gene the virus inserted into and which
exon/primer/section it attached to. The retrovirus will insert its DNA
randomly throughout the genome and if it inserts at a promoter
sequence of a proto-oncogene, the retroviral DNA cause a growth
advantage in that cell within the tissue culture.
 Transfer of human cancer cell DNA into nonhuman cells
o DNA extracted from nonhuman/mice cancer cells and analyzed
for mutations
 Chromosomal rearrangements
o Some cancers have the same breakpoint in chromosomes
o Ex: 46, XY, t(9:22)(q34;q11) = able gene moved form 9q to 22q and
created a new gene (BCR-abl) = increased abl expression =
increased proliferation since BCR gene is a very active promoter
Tumor Suppressors
 Normal functions:
 Gatekeepers – cell cycle regulation
o Prohibits propagation of mutations
o Ex: Rb, p53, cyclin-dependent kinases
 Rb – S-phase progression and regulation of apoptosis, DNA
replication, DNA repair, checkpoint control + differentiation
 p53 – expressed in response to cell damage as a
transcription factor that regulates dozens of genes that
impact growth, proliferation + survival
 Caretakers – DNA repair
o Prevents genomic instability
o Ex: BRCA1/BRCA2 (associated w/ breast cancer); mismatch repair
genes (associated w/ hereditary nonpolyposis colon cancer)
 Need TWO hits to mutate both alleles = loss of function/loss of gene expression
 Mutation of both alleles often occurs by 1) inheriting a mutation and 2)
and/or a spontaneous mutation

Inheritance Patterns
o Sporadic – spontaneous somatic mutations (first hit most likely occurs in embryo bc cell
development is extremely proliferative + exposed to oxidative damage = higher
chance of mutation)
 Ex: Retinoblastoma (Rb)
 A parent with unilateral tumor most likely sporadic due to spontaneous
somatic mutations.
 Suspected When:
 Sporadic Cancer Syndrome – isolated, unrelated cancers within a family
 70-80% of cancer syndromes
 Nonhereditary causes
 Typical age of onset
 No particular inheritance pattern
 Very low likelihood that genetic susceptibility testing will reveal a
mutation; testing will likely not provide additional information about
cancer risk
o Hereditary – inheriting a mutated cancer susceptibility gene = increased predisposition
to cancer; at the cellular level it is recessive; but appears autosomal dominant in
inheritance pattern; incomplete penetrance
 Ex: Retinoblastoma (Rb)
 A parent with bilateral disease most likely has an inherited mutation and
has a 50% chance of progeny with disease.
 Ex: Familial Adenomatous Polyposis (FAP) + Hereditary Non-Polyposis Colorectal
Cancer
 Genetic Testing of FAP tumor:
o Loss of Heterozygosity (LOH) in tumor
 Inherit one APC mutation (heterozygote carrier), lose second
normal allele in 5q21 (LOH)
o Protein Truncation Test of APC
 In vitro translation and protein analysis to see if it has loss
function
o Sequencing of APC gene** (most common)
 Full gene sequencing of all APC exons and intron-exon
boundaries appears to be the most accurate clinical test
available to detect APC mutation. Most mutations in APC
are nonsense or frameshift mutations that cause premature
truncation of the APC protein.
 Detection rate ≥ 90%
 Ex: BRCA1-Associated (breast cancer, second primary breast cancer, ovarian);
BRCA2-Assocated (breast cancer, male breast cancer, ovarian)
 Suspected When:
 Appears Autosomal Dominant transmission in pedigree
 Cancer in >2 close relatives (same side of family)
 Early age at diagnosis (<50 yrs)
 Multiple primary tumors
 Bilateral disease (paired organs)
 Rare or uncommon tumors (ex: male breast cancer, medullary thyroid
cancer)
Constellation of tumors consistent specific cancer syndrome (ex: breast +
ovary; colon + endometrial; breast + thyroid; melanoma + pancreas)
 Genetic testing encouraged
Pedigree Example:
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Autosomal dominant
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Early age of diagnosis (33,
44 <50)
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o
o
o
The same genes involved in a specific cancer are still involved (ex. APC), regardless of
whether the cancer is inherited or sporadic. The difference is the inheritance pattern
and sometimes the clinical manifestations (ex. thousands of polyps), not the genes
involved.
Familial – clustering of cancers in a family that occurred by chance or with
environmental factors.
 Suspected When:
 More cases of a specific type of cancer within a family than statistically
expected BUT no pattern of inheritance
 May result from chance clustering of sporadic cases
 Does not have trends for hereditary cancer
 Occurs in 1 or more close relatives
 Cancer may be unrelated
 Alteration in cancer susceptibility gene is NOT likely or not identified
 Genetic testing not common, but suggested if requirements met
 Pedigree Example:
 not sporadic bc elevated incidence compared to
population risk (1/4 vs 1/7)
 not hereditary bc not early age of diagnosis and
unilateral not bilateral
Genetic Testing Considered When:
 Patient has reasonable likelihood of carrying an altered cancer susceptibility
gene
 Genetic test is available that can be adequately interpreted
 Results will influence medical management
 Patient wants information (empowerment)
Personalized Medicine
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Goals for Better Healthcare
o Identification of people at risk
o Early disease detection
o Accurate diagnosis/prognosis
o Prediction of response to therapy
o Individualized dosing and drug selection
Genomic diversity – human population’s wide range of phenotypic variation is influenced by
inherited differences in DNA sequence
o SNP – single nucleotide polymorphisms
 Very common; about 1/300 nucleotides, at least 1 in every gene
o VNTR – variable number tandem repeats
 Simple sequence repeats (microsatellites, minisatellites)
o Indel – insertion/deletion of unique sequence
 Small: <1-2 kb
 Considered indel bc insertion or deletion based on what the sequence is using as
a reference
o CNV – copy number variant
 Larger (>1-2 kb) duplications or deletions
o The MOST prevalent and FUNDAMENTAL unit of genomic diversity is SNP
 SNP analysis may help identify common genetic variants associated with
common traits
Genome-Wide Association Studies – compares genomes of thousands of unrelated individuals
with particular trait to those w/o trait to identify variations that relate to probability of
developing a trait
o Goal to identify genes/markers that influence disease/traits
o Uses data from SNP array
o Output of GWS depicted on the left.
 Dots represent a SNP. There is a cutoff
and every SNP above that is linked to a
positive association between the SNP +
disease.
 Once the correlation is identified, then
people do more research to determine
biological validity of the relationship of
gene to disease.
SNP Array – type of DNA microarray used to detect polymorphisms (SNPs) within a population
o Most arrays have ~900k SNPs per
o Have catalogued over 12.8mil SNPs
o Principle: genetic variants that are near each other tend to be inherited together
 If one SNP is inherited (as represented on the microarray), then there is a decent
chance that a nearby SNP was also inherited. We can assume that the person
has BOTH SNPs based on the microarray analysis.
o Tagged SNPs – one group used to represent 6-7 SNPs as a way to compile a SNP array
 ~400k tagged SNPs cover the entire genome
Applications:
 Frequency differences may implicate genes or genetic variations associated
with disease susceptibility or progression
 Identify individuals who have disease and those who do not and if that is
associated with SNPs
 Genetic variations implicate specific genes involved in drug response
 The basis of personalized medicine: our ability to find and catalogue
common variants for common problems
Personalized Medicine – an emerging practice of medicine that uses an individual’s genetic
profile to guide decisions made in regard to prevention, diagnosis, prognosis, and treatment of
disease
o Applications:
 Predictive
 Risk of [ex: breast cancer] determined via family and personal health
history; genetic test of known susceptibility genes; SNP analysis
 Next generation risk assessments combine multiple clinical and genomic
risk factors to better stratify your patient population
 Depending on results, could individualize screening
 Early detection
 We know what kind of genes/which genes are changing at different
stages of tumor development so it is possible to test/screen for changes to
detect early adenomas
 Ex: colorectal cancer screened using stool DNA; Cologuard
 Take Home: knowing the gene mutations in cellular transformation can be
used for personalized medicine in the clinic for early detection
 Disease diagnosis
 Olden days used tissue origin, histological appearance/grade, and extent
of spread/stage
 Now use microarrays
 Ex: identifying cancer subtypes using a microarray help target
personalized medicine for treatment methods
 Molecular differences = Treatment differences
 Prognosis
 Complied using microarray data, literature review, genomic databases,
and molecular biology
 Ex: MammaPrint (first FDA-approved kit for predicting recurrence based
on expression of 70 genes); BluePrint helps further stratify patients in to
subgroups; Gene panel helps prognosis in breast cancer; Oncotype DX
predicts distant recurrence and benefit of chemotherapy
 Pharmacogenomics
Pharmacogenomics
o Knowledge of a pt’s genetic profile helps in selection of proper medication/therapy
(especially with proper dose or regimen administration)
o DNA + amino acid sequence data to inform drug development + testing
o Applications:
 Avoid serious adverse drug reactions
 Developing personalized targeted drugs
o Bioavailability impacted by gene expression
o
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o
o
o
o
o
o
Goal: maintain plasma levels in therapeutic range and personalize treatment by
developing targeted drugs based on pt’s genetic background
Serious Adverse Drug Reactions
 Deprives pts who would NOT have the adverse reaction of potentially life-saving
drugs
 Hard to define: based on seriousness of disease; presence of alternative
treatments; present in small populations
 Ex: Acute Lymphocytic Leukemia (ALL) – most common malignant cancer found
in children; standard treatment is thiopurine drug called 6-mercaptopurine. This
drug requires metabolism by protein encoded by gene TPMT. 1/300 ppl inherit 2
non-functioning alleles for this gene and therefore cannot metabolize the ALL
treatment.
 Ex: Warfarin + CYP2C9; narrow therapeutic window; individualized therapy by
measuring anticoagulant status; genetic variations of CYP2C9 can lead to
significant differences in patient response to warfarin
 Conclusion: Genetic testing can be expensive and therefore it is not a clinical
standard, but its use can provide critical information in dosing adjustments and
treatment to avoid toxicity and optimize efficacy.
Mean maintenance doses stratified by genotype (genotype frequency varies from
different racial and ethnic backgrounds)
Personalized pharmacogenomics WIDELY practiced in diagnosis and treatment of
cancers
 Ex: Herceptin/trastuzumab targets HER-2 proteins in breast cancer. The gene is
located on chromosome 17 and codes for the transmembrane tyrosine kinase
receptor protein HER-2 which acts as a growth factor. Herceptin used in
combination with chemotherapy increases survival by 25 to 50 percent versus
chemotherapy alone. Can be toxic, so use is only recommended for HER2+
breast cancer cells. So must test to know that the cancer cells are HER2+ and if
yes then more effective treatment available.
 Conclusion: there are dozens of drugs whose prescription and use depend on
target cells genetic status. Based on presence of patient’s genetic expression of
certain characteristics in target cells.
FDA is responsible for regulating pharmacogenomics.
 In the context of drug labels, these genomic biomarkers can be classified on the
basis of their specific use: clinical response + differentiation; risk identification;
dose selection guidance; susceptibility, resistance, differential disease diagnosis;
polymorphic drug targets
Challenges
 Long time frames
 Takes 10+ years to identify genes and develop effective drugs
 Environmental/epigenetic influences also impact gene expression
 EHR accessibility + changing knowledge of genetics
 Insurance coverage of genetic tests + counseling
Ethics
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Privacy + confidentiality of genetic info
Fairness in the use of genetic info by insurers, employers, courts, schools, adoption agencies,
military, etc.
Psychological impact, stigmatization, and discrimination bc of genetic differences
Reproductive issues including adequate and informed consent and use of genetic info in
reproductive decision making
Clinical issues including education of doctors and other health-service providers, people
identified with genetic conditions, and the general public about capabilities, limitations, and
social risks; and implementation of standards and quality-control measures.
History:
o Eugenics – “good in birth;” “noble in hereditary”
 “science of improving human stock”
 Early 1900s = compulsory sterilization
 Nazi “racial hygiene”
 Now, Dor Yeshorim tests for carrier risk of couples on passing on fetal conditions;
preimplantation genetic diagnosis
 Flaws:
 Assumed that intelligence was Mendelian and simple as in innate,
inherited, and non-modifiable
Policies + Laws:
o American Disabilities Act (1990) – prohibits job discrimination; prohibits state and local
gov discrimination against disabled persons; prohibits private enterprises from denying
accommodations and services based on disability
o Human Genome Project: Ethical Legal, and Social Issues (ELSI) (1990) – identify and
address issues raised by genomic research that would affect individuals, families, and
society
 Investigates:
 Genomic Research – issues that arise in the design and conduct
 Genomic Health Care - how rapid advances in genomic technologies
and genomic information influence how health care is provided and how
it affects the health of individuals, families and communities.
 Broader Societal Issues - normative underpinnings of beliefs, practices and
policies regarding genomic information and technologies
 Legal, Regulatory, and Public Policy Issues – the effects of existing
genomic research, health and public policies and regulations and the
development of new policies and regulatory approaches
o Genetic Information Nondiscrimination Act (GINA) (2008) – protects against
discrimination based on genetic information when it comes to health insurance and
employment
 Debated in Congress
 Genetic information – defined in GINA as
 Genetic tests of any embryo
 Genetic tests of any fetus
 An individual’s genetic tests (including genetic tests done as part of a
research study)
 Genetic tests of the individual’s family members
 The manifestation of a disease or disorder in family members (family
history)
Any request for, or receipt of, genetic services or participation in clinical
research that includes genetic services (genetic testing, counseling, or
education) by an individual or family member.
 Prohibits health insurers or health plan administrators form requesting or requiring
genetic information of an individual or their family and using it for decisions
regarding coverage, rates, or preexisting conditions
 Prohibits most employers form using genetic info for hiring, firing, or promotion
decisions, and any decisions regarding terms of employment
 Protects individuals against “severe and pervasive” harassment regarding
genetic info
 GINA does NOT:
 Extend to life insurance, disability insurance, and long-term care insurance
 Doesn’t mandate coverage for any particular test or treatment
 Doesn’t apply to employers w/ <15 employees
 Doesn’t prohibit health insurers from using genetic test results in making
health insurance payment determinations
 Doesn’t prohibit health insurer from determining eligibility or premium rates
based on manifestations of disease/disorder
 Doesn’t cover military, veterans, or Native Americans
o Affordable Care Act (2010) – health plans cannot limit or deny benefits or coverage for
a child younger than 19 bc of a “pre-existing condition”
Ethical Values
o Autonomy – right to refuse or choose treatment
o Non-maleficence – do no harm
o Justice – fairness and equality
o Dignity – patient and caregiver
o Beneficence – promote wellbeing of others
o Truthfulness and Honesty – informed consent
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Applications:
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
Be able to interpret: PCR results, pedigree (Mendelian), pedigree (cancer syndrome),
karyotype
Be able to predict probabilities of inheriting a disease/allele, and/or recurrence risk for an
individual (based on a pedigree or Punnet square, for example), or a population (using allele
frequency, genotype frequency and/or Hardy Weinberg)
Be able to calculate sensitivity, specificity, positive predictive value, negative predictive value
(use of scientific calculator is permitted)