List of Diseases/Disorders/Conditions detailed in
Lectures 1-9 (10-11 don’t have any new conditions)
Lecture 2: Chromosome Abnormalities: NONDISJUNCTION & ANEUPLOIDY
AUTOSOMAL TRISOMIES
Disease/Disorder
Type of mutation
Inheritance
Symptoms
Genetic Test
Trisomy 18 (Edwards
Autosomal Trisomy Non-disjunction
Mental retardation, failure to thrive, severe heart
Syndrome) 47, XX,
Typical Karyotype
defects, micrognathia, malformed ears, clenched
+18
FISH
fists w/ overlap. 2nd and 3rd digits, rocker-bottom
-screening- PAPPfeet
A is reduced in
affected
Trisomy 13 (Patau
Autosomal Trisomy Non-disjunction
Midline defects- holoprosencephaly, cyclopia,
Syndrome) 47, XX,
Typical Karyotype
micropthlamia, absence of eyes, cleft lip and
+13
FISH
palate, rocker-bottom feet, congenital <3 and
urogen. Defects
Autosomal Trisomy
Trisomy 21 (Down
1) 95% meiotic
Hypotonia, short stature, short neck, flat nasal
-Typical Karyotype
Syndrome)
nondisjunction
bridge, protruding tongue, open mouth, short
-FISH
2) 4% Robertsonian
broad hands, transverse palmar crease, IQ= 30-Screening for
translocation (14,21)
60
chromosome
3)
1%
mitotic
nondis.-congenital heart defects, leukemia, and early
anomalies requires
mosaic
onset Alzheimers
use of four analytes-First trimester screening for two analytes
MSAFP and uE3 low
Pregnancy associated plasma protein A (PAPPwhile hCG and
A) low and b-hCG (high)both placental
Inhibin are higher
-First tri. Detection- 2
products- achieve a detection rate of 75% for
analytes- PAPP-A
fetal Down
and free b-hCG
-Ultrasound measurements of excess folds of
skin increase detection to 86%
SEX CHROMOSOME ANEUPLOIDY
Turner Syndrome (45,
Sex chromosome
1) 50% by 45, X
Often detected at puberty in females
X)
monosomy
karyotype
Short stature, weebed neck, shiled chest with
-Typical Karyotype 2) 25% mosaic
wide-spaced nipples, lymphedema of hands and
3) 15% isochromosome feet, gonadal dysgenesis (streak gonads),
of X (replace p arm
primary amenhorrea, infertility, inc. risk for
with second copy of q)
cardiovasc abnormalities, intelligence normal
Klinefelter Syndrome
Sex chromosome
1) non-disj. During
Tall stature, thin and long legs, hypogonadism,
(47, XXY)
monosomy
meiosis
infertility, gynecomastia, learning difficulties
-Typical Karyotype 2) 15% Mosaic
karyotypes
Chromosome abnormalities in structure
CHROMOSOME STRUCTURE: BALANCED REARRANGEMENTS
Miscellaneous
*80% are female
*95% aborted spont.
*Infants rarely survive past 1
month,
*75-80% spont. Aborted
*Three genetic events can
account for Tri 21
*Risk of recurrence with
Roberstonian Trans. ONLY- 12%
for mothers and 3% for fathers
1/ 4000 livebirths
Only viable monosomy
1/1000 (males)
CML- Chronic
Myelogenous
Leukemia (46, XX
t(9;22)(q34;q11)
Reciprocal
Translocation
-Typical karyotype
-SKY
1) reciprocal
translocation
-fusion of 2 genes bcr-abl increased and
mislocalized tyrosine activity
- Results in dominantly active kinase CML
-Oncogenes created or activated by a
chromosomal translocation
Philadelphia chromosome= 22
Two derivative chromos carrying
material from both chrom 9 and
22
-Because bcr-abl fusion is not
found in normal cells, it is a
perfect target for Gleevec- anticancer drug
Chromosome abnormalities in structure
CHROMOSOME STRUCTURE: UNBALANCED REARRANGEMENTS
Cri-du-Chat (46, XX,
Unbalanced
1) Deletion of
Patients cry with a characteristic epicanthal
del(5p15)
rearrangement
chromosome material
folds, cat-like sound, mental retardation,
karyotype
microcephaly, low-set ears, heart defects
Prader-Willi Syndrome
(15q11-13)
Deletion of
imprinted gene
karyotype
1) Paternal deletion of
imprinted gene
2) Uniparental disomy
Morbid trunk obesity, cognitive impairment,
small hands and feet, short stature
Deletion of
1) Maternal deletion of
Children with devel. Delay, mvmt or balance
imprinted gene
imprinted gene
problems,, microcephaly, seizures, abn EEGs
karyotype
2) Uniparental disomy
Lecture 3: Molecular Genetic Abnormalities: Molecular mutations that alter INDIVIDUAL GENES
1) MUTATIONS IN EXONS
Disease/Disorder
Type of mutation
Inheritance
Symptoms
Genetic Test
Missense mutation in
Sickle Cell anemia
Autosomal coSickling of RBCs – crisis- extreme pain,
EXON- point
dominant
splenomegaly, jaundice, chronic ischemic leg
mutation in 6th aa (Bulcers
globin protein)
HbS/A= sickle cell trait- heterozygote
genotype= clinically norm but may show
-heterozygote
symptoms under low O2 pressure
detection pre-
Uniparental disomy= both copies
of an individual’s chromosomes
are maternally or paternally
derived
Angelman Syndrome
(15q11-13)
pregnancy (esp in
blacks)
-IEF (isoelectric
focusing) – first
screening
-HPLC- confirmation
-Gene therapy
Miscellaneous
Treatment- turn on expression of
fetal hemoglobin genes by drug
treatment/bone marrow transplant
*try to treat symptoms
*Heterozygote advantageincreased resistance to death from
malaria
*HbS allele is high freq (1/250)
in areas where malaria is endemic
*AFRICAN AMERICAN pop
**black male/female- hereditary
predisposition to develop
hemolytic anemia after taking
sulfa/other drugs
Neurofibromatosis
Nonsense mutation
in EXON- early
termination codon
of NF1 gene
Autosomal dominant
NF1 gene is mutated cannot inactivate Ras
highly active Ras promotes excess growth in
Schwann cells benign neurofibromas
*Lisch nodules (abn. Growths of the eye)
*café-au-lait spots- less severe form
*scoliosis, thinning of the bones in arms and
legs, seizures, learning dis, and high BP
Treatment- routine removal of
neurofibromas
*remaining normal copy is
susceptible to second mutagenic
hit
Breast Cancer
(familial)
Frameshift
mutation in EXON
-genetic linkage
study
-single gene tests
(limited bc so many
genes involved)
-Prenatal predictive
diagnosis
-Pre-symptomatic
genetic testing
Dominantly-inherited
increased risk of devel.
Breast/ovarian cancers
Inactivation of BRCA1 gene by frameshift
mutation (insertion/deletion that is not a mult of
3)
-Appearance of breast cancer in a patient under
age of 45 or cases of breast cancer in 2 or more
close relatives is from familial mut. In BRCA1
*(lecture 5)- involvement with DNA repair
pathway (ATM pathway) and genomic
instability
*BRCA2- assoc with 10-20% of male breast can
80% of patients with a mutated
BRCA1 will develop breast
cancer by age 70
-BRCA1 and BRCA2 muts
account for 5% of breast cancers
-heterozygous women
consistently lose the 2nd normal
copy 2 hit hyp.
-incomplete penetrance
Cystic Fibrosis
Mult. Of 3 ins/del in
CFTR gene
Autosomal recessive
68% of cases = F508 mut in
CFTR gene
Treatment- interventions to
minimize mucous accumulation
and treatment of infections
*whites- 1/25 chance of carrying
the mutation
-allelic heterogeneity
Autosomal dominant
Mutation loss of Phe protein misfolding
Cl- channel is defective Cl- is not efficiently
pumped out of lung cells water into lung
cells remaining lung secretions are viscous
and thick= found in lungs, pancreatic ducts,
reprod. Systems
*pulmonary infections, abn heart rhythms
-Carrier testing- test for the most common 23
CF mutations and the most common is F508
Expansion of CAG repeat in exon (normal is 635 repeats vs. 36-121+ repeats in affected)
-anticipation occurs and is manifest in the age of
onset
-CAG repeat expansion incr. size of
glutamine tract polyglutamine domain
huntingtin accumulates in nuclear inclusions or
protein aggregates
-Neuronal degeneration, increased number of
involuntary movements, dementia, seizures
Inheritance
Symptoms
Miscellaneous
Huntington’s Disease
Carrier testing
(heterozygote testing
rec.) esp for
Caucasians
-Sequence exons
only- where most
common muts are
TRINUCLEOTIDE
repeat (CAG) in
EXON of huntingtin
gene
-Prenatal predictive
diagnosis
-Presymptomatic
genetic testing
-PCR/gel electro- for
detecting repeats
2) MUTATIONS IN INTRONS
Disease/Disorder
Type of mutation
No cure
Patient usually dies within 17
years of diagnosis
Phenylketonuria (PKU)
B-thalassemia
Genetic Test
Mutation in
INTRON of
phenylalanine
hydroxylase (PAH)
gene
PKU biochemical
testing is required
for newborns
Point mutation in Bglobin gene –
prevents normal
splicing
Autosomal recessive
Trinucleotide
repeat expansion in
INTRON
3) MUTATIONS IN PROMOTER REGION
Disease/Disorder
Type of mutation
Genetic Test
Hemophilia B
Small deletion or
point mutation in
promoter of factor
IX gene
Fragile X
Trinucleotide
Repeat in
PROMOTER
region (CGG) in
Treatment- reduce dietary intake
of Phe for life
Deficient activity PAH
In absence of treatment, severe to profound
retardation occurs
Autosomal recessive
Point mutation in B-globin gene- destroys splice
site, creates new sites, enhances donor sites
Mutation reduction in B-globin production
excess alpha to beta globin subunits
precipitate destruction of RBCs and their
precursors anemia
*failt to thrive without treatment
*with treatment- regular transfusions and
chelation therapy= can live to 20-40s
Autosomal recessive
GAA expansion in intron of FRDA1 (frataxin
gene) expanded (200-900) acts as a cryptic
3’ splice site OR formation of a structure that
prevents transcription of the gene basically,
UNKNOWN mechanism
-Friedreich’s Ataxia = loss of voluntary muscle,
enlargened heart, live to avg. age of 37
Inheritance
Symptoms
Miscellaneous
X-linked Recessive
(more common in
males)
Mutation in factor XI gene prevents binding
of TF HNF-4 factor IX gene expression falls
to below 5%  deficiency in factor IX
protein fibrinogen is not cleaved to fibrin
malfunctioning in clotting cascade
*Extreme bleeding in response to minor lesions
X-linked recessive
(more males affected)
CGG expansion in promoter of FMR1
increases number of CpG dinucleotides in CpG
island of promoter when expansion > 200
repeats, CpG dinucs are methylated silenced
Treated b addition of clotting
factors from blood donors or
recombinant factor IX by genetic
engineering
*Factor VIII is mutated in
Hemophilia A (90% of
hemophilia cases)
-Southern blotting used to detect
CGG repeat expansion in
promoter and the methylation
status of the gene. DNA is
-Heterozygote
detection prior to
pregnancy
(Mediterranean;
Asians)
-Gene therapy
Friedreich’s Ataxia
Inablity to remove introns recessive allele that
produces a defective protein product protein
cannot convert Phe to Tyr incr. phe= toxic to
brain and can cause mental retardation
Variable subtypes
B0 = no detectable B-globin
B+ = variable amounts of
reduction and slightly less severe
presentation
*Italian-American or GreekAmerican have a 1/12 chances of
carrying the mutation
*Chinese have 1/20 chance of
carrying mut for Alpha-thal
FMR1 gene
In 5’UTR
-Molecular analysis
for common
mutations
-Southern Blotting
expression of FMR1 gene
-mental impairment in 1/2000 male, long faces,
large ears, prominent jaws, irregular teeth,
macroorchidism (larger testicles)
4) MUTATIONS IN 3’ Untranslated Region ((UTR)
Disease/Disorder
Type of mutation
Inheritance
Genetic Test
Myotonic Dystrophy
TRINUCLEOTIDE Autosomal dominant
repeat expansion in
3’
-Molecular analysis
for common
mutations
-Prenatal predictive
diagnosis
5) Mitochondrial disorders
Disease/Disorder
Type of mutation
Genetic Test
MERFF/MELAS
Mutation in
mitochondrial DNA
-Fragile X associated tremor/ataxia syndromeassociated with pre-mutation allele (pre-mut
allele may lead to development of FXTAS
digested with EcoRI sites flank
the promoter and a methylation
sensitive restriction enzyme
EclXI—only digests unmethyl.
DNA so it is able to distinguish
b/w expanded/ unmethylated
alleles and expanded/methylated
affected alleles
Symptoms
Miscellaneous
CTG repeat in 3’UTR of DMPK gene--?
Compromises the mRNA’s stability or makes
the mRNA a target for translational repression
by CTG repeat-binding miRNAs dec.
expression of DMPK  myotonic dystrophy
*classical symptoms of myotonia- prolonged
muscle contraction and relaxation, muscular
dystrophy, hypogonadism, frontal balding,
arrhythmia
Inheritance
Symptoms
Maternal descent- 100,000 mito in
eggs vs. 100 in sperm
Heteroplasmy- variance in inheritance
because mitochondria are inherited
with the cytoplasm in which
segregation is not regulated so fraction
of mitochondria that are inherited
varies
Miscellaneous
A woman with a mitochondrial
disorder has children who are at
risk for developing the same
disorder, regardless of their
gender. If her oocytes have a
higher % of mutant mito than her
body- she will be asymptomatic
but children can be affected
Lecture 4: Gene regulation and Development
INHERITED BIRTH DEFECTS
Disease/Disorder
Achondroplasia
Type of mutation
Genetic Test
Mutations in the
receptor for FGF
(fibroblast growth
Inheritance
Symptoms
Miscellaneous
Inherited birth defect
Mutations in FGF receptor activate the
FGFR3 receptor even in absence of
ligand inhibition of chondrocyte
Controversial therapies
1. growth hormone therapy
2. surgical lengthening of lower
factor)
Holoprosencephaly
proliferation within the growth plate
shortening of long bones and abn.
Differentiation of other bones
Mutations in SHH result in vastly different
phenotypes bc there are diff in modifier
loci variable expressivity
legs
Sex determination is very
sensitive to gene dosage- some
XY individuals who are
heterozygous for certain genes
are sex reversed and develop as
females bc a single dose of these
genes (SOX9, WT1, or SF1) is
not enough for normal testis
develop. HAPLOinsufficient
8% of all pediatric cancers
1) 25-50%
chromosomal abn.
2) 30-40% single
gene (SHH gene)
defects
3) mutations in
SHH gene, TGIF,
SIX3, ZIC2
Point
mutation/del/translo
Of SRY gene
Inherited birth defect
Inherited birth defect
SRY XY female- appear normal but lack
copy of 2 X, do not develop secondary
sexual characteristics, don’t menstruate,
have streak gonads
SRY XX males- develop as males but
missing critical genes from Y- unable to
promote normal sperm develop.
Believed to develop
from malignant
transformation of
renal system cells
that remain undiff.
-WT1 gene,
glypican-3 gene
affected
Lecture 5: cancer genetics and Genomics
CANCER
Disease/Disorder
Type of mutation
Genetic Test
Sporadic
Oncogene-based
tumors
Inherited birth defect
Associated with WAGR syndrome that is
characterized by susceptibility to Wilem’s
tumor
WT1 gene- complex- encodes multiple
proteins- a modulator of transcription
Inheritance
Symptoms
Sex reversal
Wilms’ Tumor
Both genetic and envt.
Causes
Can be caused by ingestion
of cyclopamine (from corn
lilies)
Acquired mutations in
oncogenes such as ras, myc,
src
Act in a dominant fashion
Homozygous Recessive Mutations  cause Chromosome instability syndromes
Xeroderma
Mutation in gene
Autosomal
Nucleotide excision repair is defective problems
pigmentosum
required for
recessive
with repairing the type of damage in DNA upon
Nucleotide excision
exposure to UV radiation
Show variable expressivity
Genetic heterogeneity= cam ne
caused by mutations in multiple
genes
Locus heterogeneity- mutations
in diff genes can case the same
clinical phenotype
Miscellaneous
Wear UV protective suits, get
significant sunburns/ blistering,
median age for skin cancer = <10
Ataxia telangiectasia
Fanconi anemia
Bloom Syndrome
repair
Mutation in ATM
gene
Genetic lesions in
proteins interacting
with ATM gene
-heterozygote
testing rec.
Mutation in a
protein complex
that interacts with
ATM/Fanconi prot
-heterozygote
testing rec.-
Autosomal
recessive
Autosomal
recessive
Autosomal
recessive
Hypersensitive to ionizing radiation bc ATM mutation
prevents proper DNA damage repair for doublestranded breaks
*symptoms = loss of balance, slurred speech during
toddler years, cerebellar degen, radiosensitivity,
sterility, immunodeficiency, pre-disp to develop
tumors
Sensitive to ionizing radiation and agents that cause
double-stranded breaks
*symptoms- bone marrow failure, skeletal abn,
increased risk of malignancy
Acutely sensitive to ionizing radiation
*symptoms- severe growth deficiency, early
menopause, recurrent infections, more susceptible to
tumor-devel
yo
Patients should be spared repeated
exposure to radiography and have
surveillance for tumor development
Higher prevalence in Ashkenazi
Jews.
Patients should be spared repeated
exposure to radiography and have
surveillance for tumor development
Patients should be spared repeated
exposure to radiography and have
surveillance for tumor development
TUMOR SUPPRESSOR GENE INACTIVATION
Retinoblastoma
Mutation in RB1 gene
(tumor sup gene)
(TSG)
Although TSG
harbor recessive
loss of function
mutations, they
appear to be
inherit. In a
dominant fashion
Two-hit hyp- hetero carrier of RB1 mutation has a
high prob of getting a second mutation in the good
copy retinoblastoma tumor
*Acquiring a hereditary mutation in TSG predisposes
an individual to the effects of a loss of heterozygosity
(LOH) = dominantly inherit. The predisp for
acquiring a mutation in the single wild type allele
Li-Fraumeni syndrome Mutation in p53 gene
P53 important for cell cycle regulation.
Mutant p53 predisposes individual to a large variety
of cancers that arise when second copy of p53 is inact.
OTHER CANCERS – Mentioned in regards to expression profiling in cancer diagnostics
Disease/Disorder
Type of mutation
Inheritance
Symptoms
Genetic Test
Diffuse Large B-cell
Expression profiling,
Two main subtypes of DLBCL
Lymphoma (DLBCL)
hierarchical clustering
1) germinal center b-like subtype had more fave
outcome
2) activated b-like subtype less fave.
Breast cancer
Expression profiling
Two subtypes- Her2 and luminal epithelial cell-like
tumor types- different response for each to taxol
treatment basal epithelial < luminal epithelial
Incompletely penetrant- some
pp have the predisposition for
RB but don’t develop
Miscellaneous
Importance of testing to
differentiate bw two subtypes
Importance of testing to
differentiate bw two subtypes
Prostate cancer
survival rate
Two subtypes id- each subtype seemed to correspond
to upreg of expression of a particular small set of
biomarkers- these signs could serve for faster single
gene tests for prostate cancer
Expression profilinghierarchical clustering
Lecture 7: Genetic Screening and Prenatal Diagnosis
Disease/Disorder
Type of mutation
Inheritance
Genetic Test
Hemochromatosis
Most common
Autosomal
mutation- (C282Y)
recessive
-DNA analysis
-Population screening
Symptoms
Miscellaneous
Iron overload disorder- primarily affects the liver
(cirrhosis), heart, pancreas (diabetes), skin (bronzing)
and testes (atrophy)
-**Affects Caucasians- 1/10 but
fewer because of reduced
penetrance**
-Population screening is more
controversial than DNA analysis
Frequency of abnormalities relates
to degree of elevation of maternal
Phe during pregnancy
Maternal PKU
-Newborn screening
Congenital
hypothyroidism
-Newborn screening
via measurement of
thyroxine followed by
TSH
Usually
sporadic
Non-syndromic
Deafness
-Two Connexin-26
gene mutations (mst
common)
-Mutation in connexin30 gene
DNA mutation analysis
-heterozygote detection
prior to pregnancy
Autosomal
recessive
If uncontrolled results in about double the risk for
spontaneous miscarriage (24%) and increased risks of
intrauterine growth restriction for fetus (40%)
microcephaly (73%), psychomotor retardation (92%),
congenital heart defects (10%)
Deficient in circulating thyroid hormone, thyroxine
-prolonged jaundice, enlarged tongue, abdominal
distension, muscle hypotonia, delayed skeletal
maturation,
-Failure to initiate timely treatment = neurologic
damage w/ mental retardation, growth retardation
Goal is to initiate treatment within 3 weeks of birth
Non-syndromic deafness is not associated with
additional abnormalities
Tay-Sachs Disease
Screening for
heterozygotesHexosaminidase A
screening
Blood sample
DNA analysis for
common mutations
Screening for
Autosomal
Recessive
Affected children usually die between ages 2-5- fatal
neurodegenerative disease
Canavan disease
Importance of testing to
differentiate bw two subtypes
Severe neurodegenerative lethal condition with death
1/4000 babies born
-Racial/ethnic differences
-Black infants have 50% the rate of
white infants
-Hispanics have 40% higher than
whites
-Common mutation or common
Ashkenazi Jew mutation
*Whites- have a 1/31 chance of
carrying the mutation
-Prevalent in Ashkenazi Jewish
population but with success of
screening, number of Tay-Sachs
births to Ashkenazis is less than
those for non-Ashkenazi jews
-Increased frequency in French
Canadians too
-heterozygote frequency
heterozygotes=Detected
prenatally-DNA analysis
for 3 mutations assists in
detection of heterozygotes
Familial dysautonomia
-Molecular analysis for
common mutations
Screening for
heterozygotes- DNA
analysis for 2 mutations
assists in the detection
of heterozygotes in
99% cases
often by 10 years of age
approximates 1/40 Ashkenazi jews
-Ashkenazi jew- 1/40
Progressive neurodegenerative condition that may
have a variety of sensory/neuronal disturbances and a
decreased life expectancy
Common features include alacrima (lack of tearing),
absence of lingual fungiform papilla, impaired taste,
hypoactive or absent deep tendon reflexes, vasomotor
instability, indifference to pain and temp
Lecture 8: Testing for disease susceptibility
Disease/Disorder
Type of mutation
Inheritance
Symptoms
Genetic Test
Disorders in chapter but already detailed above: Huntington’s disease, PKU, CF, Fragile X
Duchenne’s Muscular
X-linked dystrophin
x-linked
Progressive deterioration of muscle tissues and
Dystrophy (DMD)
gene
recessive
weakness in the childhood yrs- most patients unable
-linkage testing in
to walk at 12 years old.
families
Lecture 9: Genetic Frontiers
Disorders in chapter but already detailed above: SCID, Sickle cell anemia, Hemophilia B, B-thalassemia, CML
Disease/Disorder
Type of mutation
Inheritance
Symptoms
Genetic Test
Acute Lymphoblastic
Childhood leukemia caused by low activity of TPMT
Leukemia (ALL)
Pharmocogenetics used
enzyme—> prevents methylation and inactivation of
as a treatment to detect
6MP accumulation of 6MP converted into a toxic
low TPMT activity
byproduct that inhibits DNA replication
Diabetes
Microarray analysis
Complex disease in which microarray is used to
determine factors contributing to disease
Obesity
Microarray analysis
Complex disease in which microarray is used to
determine factors contributing to disease
AIDS
Gene therapy via RNAi
delivery of genes
Miscellaneous
Miscellaneous
Charts specific for lectures 6-9
Lecture 6: ID Genetic basis of disease Phenotypic Variability
Markers for variability
SNPs- Single Nucleotide Polymorphisms
Loci in the genome where the sequence
varies at the position of a single nucleotide
from person to person
Alternative splicing
Mechanism of genome variation uses
different combos of splicing sites from the
same gene to produce mature mRNA
molecules that exhibit differential use of
the gene’s exons= protein products with
different combos of segments encoded by
various exons
Copy Number Variation (CNV)
Regions of the genome that differ in the
total number of copies per genome in diff
people. Can include regions that are
deleted, duplicated, inserted, otherwise
altered
-Bias AGAINST deletions in genecontaining regions vs. bias FOR
duplications in gene-cont. regions
Epigenetic modifications
Contribute to phenotypic variability as seen
by 50% of genes that show 2-4 fold allelic
variation in expression levels
-results from differential expression of
genes, particularly at imprinted loci
-differences in long-range enhancers can
also lead to variability
0.1% of genomic variability
-3 SNPs/ kilobase (3 million SNPs)
-80-85% in exons
-1500 unique sites of CNV
-12% of the genome
Lecture 6: ID Genetic basis of disease
Study designWhat it tests for: Tests for genetic Basis but does not investigate
Genetic Basis of Disease
what the specific genetic contributions are
Familial clustering
Tests for a genetic basis
Compares the probability of developing a disorder for a relative of the
affected proband versus a member of the general population
Twin studies
Adoption studies
Study designLinkage studies
Standard Linkage analysis-
Affected Sib Pair Analysis
Tests for a genetic basis
Compare concordance of developing the disorder in monozygotic vs.
dyzygotic twins where concordance= the phenotypic similarity of the
pair of twins in question
Tests for a genetic basis
Strong method of identifying the role of genetics in disease
Scientists compare monozygotic twins who have been raised in
different families to see if they show the same propensity toward
developing a disease- nature vs. nurture
What it tests for: Tests to identify the genes themselves that lead to
a particular phenotype
Based on the principle that genes whose loci are close together will
often be inherited together. Understand the Mechanism by which
genes sort during meiosis easiest level of sorting is with
chromosomes themselvesfirst separate from homologs then from
sister chromatids resulting gamete has a single copy of each
chromosome, purely by chance. Through meiotic recombination,
genes are randomized so an ind. Will inherit maternal chromosome
that is a combo of both their mother’s chromosomes. Genes that are
close to each other are often inherited together = linked genes
LINKAGE ANALYSIS- takes advantage of this and looks for loci that
seem to segregate more often with the disease phenotype than with
chance search for markers that show an overrepresentation of nonrecombinant offspring with the parental haplotype
-subjects from families with multiple cases of a partic. Disease are
genotypes and the markers are analyzied to id a locus where the
particular allele seems to cosegregate with the disease at a sign. Freq.
-Then construct a haplotype (series of alleles found at linked loci on a
single copy of a chromosome) and compare- est. a region of interest
then use Human Genome project to determine genes in that region
Complication- require specific and hard to find family structure
Alternate study design that relies on the principles of linkage seeks to
Result
Those disorders that are influenced by a genetic
contribution will show significantly increased
risk for immediate fam members amd modestly
inc. risk for distant fam members
If disorder is genetic basis, higher degree of
concordance in mono vs. dizygotic twins
Practically, to id monozygotic twins who know
their biological origins, who have one or both
siblings who are affected by a particular
condition is a difficult proposition. Not used
often.
Result
-To identify loci throughout the genome that
might be linked to the disease gene, linkage
analysis uses a panel of silent DNA markers
-Three types
1. RFLPs
2. SSLPs
3. SNPs
These linked markers should be transmitted
alongside the disease gene a high fraction of the
time, and mathematical analysis in the form of
LOD score can confirm that these cotransmissions are stat. significant and due to
tight genetic linkage.
-parametric analysis- requires use of a genetic
model that describes the mode of inheritance,
penetrance, the gene freq, and the # of loci
involved
-Large pedigrees with mult cases of affected ind
needed to gain enough statistical power
-Potential problem- DNA samples aren’t
id loci throughout the genome that segregate with the disease trait
-Uses samples only from affected siblings who can share 0, 1, or 2 of
their marker alleles but if a certain marker is linked to a disease gene,
one would expect to see a skewing of the distribution of allele sharing
in affected siblings.
-Next step- evaluate the statistical significance for the various marker
loci tested
Complications- cannot distinguish IBS from IBD
Study designAssociation studies
Case control study
Transmission disequilibrium
test
What it tests for: Association studies specifically look for a
statistical assn between an allele and a disease phenotype in the
general population = linkage disequilibrium
Design: most common study design in the genome-wide assn study
group (GWAS). Divide the population into 2 groups, the affected
group and an unaffected control group look for a diff. freq of marker
alleles bw the two groups no need to find subjects with any
particular family structure but the control group must be PERFECTLY
matched
Complications- any imperfection in control matching can result in
spurious associations
Developed to avoid complications of doing a case control with
imperfectly matched controls
-Internal controls in the form of parental genotypes measure the
deviation from expected transmission of a maker allele from a hetero
to its affected offspring
-SNP markers useful because they are less mutable and are more
densely spaced
-complication- requires parental samples
collected from the parents of the affected and so
it isn’t possible to distinguish between situations
where allele sharing results from Identity by
state or identity by descent.
IBS= when both parents have a copy of the same
allele for a given marker locus
IBD= two siblings inheriting the same copy of
an allele from the same parent
Correct for this by choosing a marker (SNP) that
has multiple, LOW FREQ alleles = less likely
that the 2 parents will have the same allele for a
given marker
Miscellaneous
Example of case control gone wrong- chopstick
study where it was found that “a gene exists
which controls both eye color and ability to use
chopsticks” except that the two groups were not
controlled for ethnically.
If a marker allele is not associated with a
particular phenotype, then it and the second
allele in the hetero parent should be transmitted
to an affected offspring with equal probability
-If a marker IS associated with a disease
phenotype, then it will statistically
OVERTRANSMIT to affected offspring
General Principles for Screening:
1. The disorder should be an important problem (morbidity and mortality), such as common occurring conditions
2. The disorder or condition should be common (prevalence and incidence), sufficiently high so cost-benefit is justified. Screening for a disorder
of short duration is not recommended. Rather, those with long pre-clinical duration (breast, cervical, colon cancers) offer opportunity for
benefit from screening.
3.
4.
5.
6.
The disease/condition should have a readily available and acceptable treatment or remedy
Screening tests should be accurate in terms of sensitivity (high), specificity (high), and predictive value
Screening should be relatively inexpensive- benefits should far outweigh costs
Screening procedures should be acceptable by both patient and society- tests should be safe and provide a minimum of discomfort
Lecture 7: Genetic Screening and Prenatal Diagnosis—types of genetic screening
Screening Type
Description
Mass screening of a population for bp, blood sugar or cholesterol levels
Population Screening
aims to assist people in recognizing that they need special medical attn bc
of their risk profile
Newborn Genetic Screening
Screening for Heterozygotes
Mandated in all states for specifically named biochemical genetic
disorders
Key elements of BIOCHEMICAL GENETIC screening are to recognize
disorders for which treatment is necessary in order to avoid develop of
mental retardation
-screening for Severe Combined Immunodeficiency (SCID) –disorder that
is uniformly fatal by one year if not treated with a bone marrow
transplant- before 3 months has the best outcome—most affected
individuals do not have a family history so newborn screening is a good
strategy. Affected have low or absent T-cells tests quantify T-cell
receptor excision circles (TRECs). Normal individuals will have a high
number of TRECs while those with SCID will have decreased #s at birth
and few detectable TRECs
-Hearing loss screens- 50% of hearing loss is inherited; 70% of which is
non-syndromic vs. 30% assoc with addl abnormalities (syndromic)Mutation Analysis
Screening for Tay Sachs-disease- screening by assay for the lysosomal
enzyme hexosaminidase A if half the activity of the enzyme =
heterozygosity for Tay Sachs it is less reliable or when the patient is
taking an oral contraceptive
-A more reliable test is a second blood sample or DNA analysis for the
common mutations= 98.6% accurate
-Hexosaminidase A screening is extremely effective bus also associated
with a number of false pos results- largely related to the serum
hexosaminidase assay being done during an est. pregnancy w
-success of screening has reduced the number of Tay-Sachs births to
Ashkenazi Jewsand more affected babies are born to non-jewish couples
Examples
Pap-smears to detect cervical cancer
Prostate cancer screening- men > 50 years
Mammography- for breast cancer
Colon cancer- stool screening
Transferrin saturation- best test for diagnosis of
hemochromatosis
-PKU
-Congenital hypothyroidism
-Inborn errors of metabolism including
Galactosemia, Maple Syrup Urine disease-CF (but controversy because CF screening often
associated with false pos. results and some evidence
suggests that early diagnosis may make no
difference
-SCID- 1/50,000 births
-Newborn hearing screening programs- institute
early intervention (hearing aids).
-non-syndromic deafness- most common cause is
having 2 connexin-26 gene mutations- use DNA
mutation analysis
-Prevalent in Ashkenazi Jew population— between
1/27 and 1/30 Ashkenazis carry a Tay-Sachs gene
mutation with about 1/3600 births being an affected
ind.= 100x more frequent than non-Ashkenazi
-Increased frequency among French-canadians
where the carrier risk is similar to that for Ashkenazi
Jews
-Screening for heterozygotes- carrier frequency is at
least 0.5-1% and are found frequently in
Ashkenazim = Bloom syndrome, Fanconi anemia,
Gaucher Disease, Maple syrup urine disease,
mucolipidosis type IV, Niemann-Pick disease type
Screening in Pregnancy
Diagnostic procedures1. amniocentesis
2. chorion villi sampling
3. cordocentesis or PUBS
4. ultrasonography
or couples of mixed Jewish/non-Jewish parentage
-Aim of maternal serum screening is to ID pregnancies where the fetus has
a serious defect such as neural tube defects or a chromosome anomaly
such as down syndrome
-screening developed bc 95% neural tube defects occurred without prior
history and 95% of Down syndrome infants were unexpected too
-Quadruple Screening in the 2nd trimester involves the assay of maternal
serum for alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG),
unconjugated estriol (uE3), and serium Inhibin
-Assay for acetylcholinesterase inclines diagnosis towards neural tube
defect, but is not absolutely specific for that lesion
-elevated AFP directly from fetus to maternal circulation can indicate
problems with placenta—indicated by elevated MSAFP= pregnancy at
higher risk for later obstetrical complications
-Amniocentesis for prenatal genetic studies is recommended when odds of
Down syndrome is 1/270
A, glycogen storage disease type 1A
-Maternal serum AFP= MSAFP= if elevated 
increased leak of this protein into the maternal
circulation leakage from an open defect such
as spina bifida, anencephaly, or encephalocele
raises the conc. In the surrounding amniotic
fluid and the maternal serum as well
-Other defects that leak AFP directly into
amniotic fluid – renal defect, autosomal
recessive weeping skin defect
-Leak of neuronal origin, Acetylcholinesterase
is also spilled into amniotic fluid
-screening for Down syndrome, neural tube
defects –anencephaly,
Lecture 7: Genetic Screening and Prenatal Diagnosis
SCOPE FOR PRENATAL DIAGNOSIS
CYTOGENIC DISORDERS
BIOCHEMICAL GENETIC DISORDERS
MOLECULAR GENETICS
Detection of all recognizable chromosome anomalies, use of FISH for rapid diagnosis of
numerical chromosomal disorders/structural rearrangements including
deletions/duplications/translocations
-Detection of >100 biochem metabolic disorders by enzyme analysis of amniotic fluid cells- ex.
Tay-Sachs (Hexosaminidase A assay), Hurler syndrome (alpha-iduronidase)
-Complication- the many diff mutations in each disorder makes mutation analysis
impractical/costly except for Tay-Sachs and Canavan’s disease
-so enzymatic analysis remains the accepted method for majority of inborn errors of metabolism
-Detection of any recognized mutation is now possible, through PCR and if needed, gene
sequencing of DNA from amniotic fluid cells/ chorionic villus tissue
-For disorders in which gene loci have been discovered but mutation detection is too costly, DNA
linkage analysis is used (95-98% certainty)
-Molecular analysis for common mutations include: Canavan disease, CF, duchenne/Becker
muscular dystrophy, fragile X, gaucher, Myotonic MD
-Heterozygote detection prior to pregnancy: CF (Caucasians), sickle-cell (Blacks), Tay-Sachs
(Ashkenazi Jew/ French-Canadian), thalassemia (Mediterranean; Asians)
-Paternity Testing
PRENATAL DETECTION OF LEAKING FETAL
MALFORMATIONS
Problems encountered in PRENATAL DIAGNOSIS
-Prenatal Predictive diagnosis- diagnostic tests that accurately predict serious-fatal genetic
disorders that many manifest decades after birth. In absence of a cure, couples with a 25-50% of
having affected offspring consider this testing – neurodegenerative disorders/ neuromuscular
disorders, or those with inherited cancer. Ex. Huntington’s Disease, myotonic muscular dys,
sponcerebellar ataxia, hereditary breast/ ovarian cancer or colon cancer
Analysis of amniotic fluid for AFP opportunity to detect fetal defects that leak fetal serum
indicative of open spina bifida, anencephaly, omphalocele, etc.
-Optimal time for detection – 16-18 weeks of gestation
-Exception 5% of spina bifida lesions are closed and don’t leak  false negative because of
skin-closed lesion
-Acetylcholinesterase- found in the amniotic fluid when a neuronal leak is present
1. Pseudomosaicism- results when cultivated amniotic fluid cells with an abnormal karyotype in
a single tissue culture dish arise as an artifact of cell culture or as a derivative of placental tissue
not rep. of the fetus. True mosaicism is distinguished by the finding of cells with both norm/abn
karyotypes in the SAME amniotic fluid specimen in at least TWO cell culture dishes
2. Multiple fetuses-discordancy for specific defects (i.e. one fetus has Down syndrome and the
other has spina bifida)
3. Cell growth failure (rare)- bacterial/fungal infection may ruin a sample as may excessive heat
or cold. Toxic substances within syringes/tubes may also prove lethal to amniotic fluid cells
4. Maternal cell contamination- maternal cells may adhere to the amniocentesis needle and
cause serious erros in prenatal diagnosis
5. Unexpected diagnosis- prenatal genetic studies performed for specific indications may reveal
an unexpected diagnosis. Ex. XYY male. Refer for genetic counseling
Lecture 8: Testing for disease susceptibility—Types of testing
Abnormal events during meiosis can cause disruption of normal
Genetic testing:
chromosome number/structure
Chromosomal abnormalities
-Traditional karyotype- allows visualization of metaphase
chromosomes- resulting banding patterns can be used to id
chromosomes, determine how many homologs of each chromo are
present, and visualize any large structural rearrangements
-SKY- simplifies typical karyotype- paints each chromosome a dif
color using labeled DNA probes that target specific chromosomes –
ID large-scale chromosomal rearrangements
Genetic testing:
Direct mutation testing
expect to see 2 of each – contrasting colors make the presence of a
translocation obvious. Downfall- requires amplification
-FISH- no amp needed, use probes directed towards a particular
chromosomal region- can id changes in chromosome copy number, if 2
probes from diff chromosomes co-localize = translocation. Should
verify with full karyotyping
-PCR- amplifies a specific genetic sequence which is further studied
for characteristics of size or sequence and this amplified sequence is
targeted by designing unique DNA primers that flank the region of
interest thermocycling PCR reaction amplifies the number of
copies of target sequence
-Gel electrophoresis- separates DNA fragments by size by pulling
negatively charged DNA particles towards the anode and the mobility
of the DNA fragments depends on their size, smallest move fastest
-Southern blotting- Alternative technique used to detect large-scale
changes that can’t be amplified by PCR= ex. Triplet expansions in noncoding regions that have size changes larger than those found in the
coding region. Southern blotting—genomic DNA is digested with
restriction enzymes and run on a gel restriction enzymes cut the
DNA at periodic intervals produces a collection of DNA fragments
 put on nylon membrane labeled probe is hybridized to the unique
complementary sequences on the membrane and visualized using x-ray
film
-Dideoxy Sanger sequencing- Detect single basepair changes; most
widely used method for sequencing genes directly; id single base pair
sequence changes. A DNA sequencing method using a mixture of both
deoxynucleotide triphosphates (dNTPs) and dideocynucleotide
triphosphates (ddNTPs) in a rxn that is related to the PCR rxn. If a
dNTP is added to the growing DNA chain, then a 3’OH is present to
continue addn of nucleotides; if a ddNTP is added, it is missing 3’OH
and addition is not possible.= Forms characteristic sized molecules and
ddNTPs are colored, separated by electrophoretic techniques=
converted into linear DNA sequence.
- Allele specific hybridization- Method used to detect single basepair
changes, similar to Southern blot, but doesn’t separate DNA by size;
instead, complete genomic DNA is hybridized to a spot on nylon
membrane spot is probed with a labeled oligonucleotide which only
hybridizes to normal or mutant allele membrane exposed to x-ray
film presence/absence of signal will indicate which alleles are
present (SKIP electrophoresis)
Genetic changes on the nucleotide or gene level
-Combination of PCR and gel electrophoresis
detect deletions and insertions large enough to
cause a chance in DNA migration (less than 10100s of basepairs)
-PCR/gel electro- Used to detect Huntington CAG
repeat- can predict with high accuracy, the
likelihood of an ind. Developing Huntington’s
based on the CAG repeats
-Southern blotting used to detect large-scale
deletions and insertions- detect non-coding triplet
repeat expansions and also able to detect
methylation status of a gene
-Southern blotting- used for Fragile X
-Both dideoxy-sequencing and allele specific
hybridization are good at detecting single basepair
changes; also designed to id mutations in small
regions of genes but most disorders have some
level of allelic heterogeneity – aka a condition that
can be caused by multiple mutations (PKU, CF)
ALTERNATIVES
-Complete exon sequencing- So, typical genetic
test for a disease with a high level of allelic
heterogeneity = sequence only the exons= where
the most predictable mutations are.
-Panel of mutations- testing strategy is further
focused by testing for a panel of mutations that
represent the majority of mutations present in a
given population
-Focus mutation= if a particular mutation is
identified in a patient by a broader sequencing
method, family members can immediately focus on
Genetic testing:
Linkage testing
Test specific for disease
-Linkage testing is used if a patient exhibits disease that is suggestive
of a particular disorder but no mutations can be identified by exonic
sequencing.
-Linkage tests take advantage of the same principles that guide linkage
ANALYSIS in id-ing a disease gene
-Use markers that lie close to the disease-gene because they are often
inherited with the disease gene
 RFLPs can be detected by Southern analysis or amp by PCR
 SSLPs differ in length of repeat tracts and these differences can be
detected by PCR and gel electrophoresis
 SNPs- identified by DNA sequencing, by restriction digest, by allele
specific hybridization
Markers for test are generally chosen based on 2 criteria: proximity to
the gene and heterozygosity in the population
-marker based genetic tests are useful in detecting Uniparental
Disomy (UPD). Compare the haplotypes of both the suspected UPD
chromosome and a control chromosome in the affected patient and
his/her parents
-CF sweat test- detect elevated levels of ions present in the sweat of
individuals with defective chloride channels
-PKU biochemical test- measure the blood concentration of Phe in
newborns
--Problem1. elevated levels may not show for a few days after birth and may go
undetected)  this wouldn’t happen with a genetic test which would
thoroughly evaluate the gene
2. Biochemical tests do not yield insight about carrier status
-Hemoglobinopathy- biochemical testing that can provide info about
carrier status—two main types of testing used to screen for sickle cell
anemia and various thalassemias
1. Isoelectric Focusing (IEF)- specialized form of protein
electrophoresis that separates hemoglobin subunits within the gradient,
the mutation present in the family rather than
complete exonic sequencing
-Linkage testing used for a family with a history of
Duchenne’s muscular dystrophy (DMD) – gene is
HUGE= 2.5 megabases (10x size of CFTR gene)so complete sequencing is less practical.
-Linkage testing is carried out using 2 markers
flanking the dystrophin gene. Although markers
are chosen close to the disease gene, this doesn’t
completely rule out the possibility of recombination
skewing the results of this type of genetic test
-UPD- chromosomes present are the same copy
from the same parent= can lead to appearance of
recessive disorders for which the parent is a carrier
-Genotyping of markers on the suspected UPD
chromosome can determine if both copies of a
particular chromosome are derived from a single
parent’s chromosome
- If a UPD chromosome exists, the marker loci
would all be expected to be homozygous for one
parent’s alleles
-One caveat- linkage genetic tests and marker tests
for UPD require multiple heterozyg. Family
members and at least 1 affected member or marker
can be separated from disease gene by recomb.
but relative quantities of the variant hb are more difficult to determine
2. High performance liquid chromatography (HPLC)- More
accurately estimates quantities of hb variants, but more expensive
Conclusion: The decision between biochemical and genetic testing comes down to a cost-benefit analysis. Generally, testing is recommended for
individuals where medical decisions and treatments would be informed by test results (i.e. not adult-onset disorders). In terms of cost benefit, FULL
GENE SEQUENCING would be the most informative but it is extremely costly making it inaccessible to most. Instead, goal is to offer MUTATION
PANEL TESTING or COMPLETE EXON SEQUENCING, depending on the disorder/circumstances. Where there is a case of a known affected
individual in a family, this individual should be tested first to id which mutation is travelling within a given family.
Lecture 9: Genetic Frontiers
Method
Description
-Thousands of DNA substrates bound to a solid surface in a highly ordered configuration. Each spot on the array corresponds to a
Microarray
technology aka gene known, unique DNA sequcnce. Once the DNA is bound, it can be probed using labeled DNA. The DNA probes are derived from
experimental samples and are labeled with fluorophores. When the DNAs find a complementary sequence on the chip, they bind to that
chips/ DNA chips
sequence. The whole chip is scanned for fluorescent signal and any spot where signal is detected can be traced back to the original key
of spots to determine which unique genomic locus has been detected.
-Used for SNP genotyping detection of a signal indiciates presence of a particular SNP allele. Makes using a large collection of SNPs
more feasible in linkage analysis
-This type of high-throughput genotyping has allowed for the trend of using large genome wide association studies (GWAS) = vast
catalogue of genes associated with disease helpful for complex diseases like obesity and diabetes
-Microarrays used in direct-to-consumer tests
-Microarrays used to id a novel coronavirus (SARS-CoV) which was the cause of SATS
Direct-to-consumer
-Private interests saw the profit potential and moved quickly to commercialize this info into genome-wide DIRECT-TO-CONSUMER
tests
tests which have positive benefits such as extending preventative testing to people who might not otherwise be identified until seeing a
(An application of
specialist
Microarray test)
-Problem- worry that patients will seek out genome-wide scans and not know what to do with the info after. A professional should be
involved in interpretation of results.
Comparative
-A comparison is made between 2 diff signals which is useful for detecting polymorphic copy number variations or abnormal copy
Genomic
numbers of genes such as deletions or amplifications, freq associated with tumorigenesis.
Hybridization
-Control = green and experimental sample = red two DNA samples are mixed and hybridized to a chip locus amplified in the tumor
(An application of
= red and deleted locus = green
Microarray testing)
-When used in conjunction with comparative genomic hybridization, can detect microdeltions probes loci spaced every 35 basepairs
High density
along chromosomes.
microarray
Conclusion: Microarray-based technologies help the id of loci associated with particular disease and id of the disease gene itself.
Expression profiling
(application of
microarray test)
Gene Therapy
1) REPLACE gene
-Act. Paralogs
-Wild type copy of
gene
-Viral machinery to
deliver genes
-Expression profiling- id patterns of gene expression associated with particular disorders. Understand the interplay of numerous genes
in promoting a disorder. Highly objective and precise, esp in determining tumor subtypes, prognosis, progressiveness related to
treatment strategies and id of biomarkers.
-Technique of gene therapy is to make use of an individual’s own genes to supply functional copies of genes that are mutated.
-Sickle cell anemia and Beta-thalassemia- Ex. Used in sickle cell anemia by using a functional paralog (homologous gene within the
same organism) of the B-subunit that normally acts during the fetal period. This subunit (with butyrate treatment) can displace the
mutant HbS protein. Also used in B-thalassemias
- When paralogs are not available, wild type copies of gene from outside source is used through safe and effective gene delivery,
including the use of naked DNA or of liposomes which are synthetic lipid bilayers that can be made to carry specific DNA molecules.
TWO DRAWBACKS to this method- nonspecific and inefficient
-Developed replication deficient viruses which could carry and deliver recombinant DNA to certain target cells; the modified viral
genome itself doesn’t have copies of key genes needed for the viral life cycle. All the genes needed to produce an infectious viral
particle are present but once these particles are used to infect normal human cells, the viral genome is incomplete and cannot produce
addl viral particles. Over 60% of these trials are used for cancer therapeutics.
-SCID- The most promising trial involved severe combined immunodeficiency (SCID). Gene was delivered to allow expression of T
and NK cells which are mutant in the disease. However, after 30 months, 2/11 patients developed acute lymphoblastic leukemia (ALL)
bc the viral genome integrated with the patient’s LMO2 locus, activating the oncogenes.
-Before gene therapies can be widely accepted, issues of safety and efficacy need to be addressed. It is advised to use bone marrow
transplants before gene therapy for SCID.
2) Use of RNAi
-Small interfering RNAs (siRNA) and an RNA-induced silencing complex (RISC) target homologous mRNA for cleavage. If
engineered siRNA molecules could be delivered by viral mechanisms, this could allow for sequence-targeted inact. Of genes
-HIV- Ex- Proposed that this technique could be used to inactivate expression of CCR5, the HIV coreceptor to prevent HIV infection of
CD4 + cells.
-Cancer – RNAi could be used to inactivate cancer genes such as bcr-abl by engineering siRNA molecules that bridge the fusion
junction
3) Stem Cell therapy
(cell-based delivery
of genes)
-Two main forms: treatment with embryos (advantage = cells are totipotent- potential to become any cell type but problem might be
difficult to find an HLA match) and treatment with adult stem cells derived from the patient himself (pluripotent- potential to become
many but not all cell types, HLA will match).
-Induced pluripotent stem cells (iPS)- using tissue derived from adult mouse or human in which these differentiated adult cells were
reprogrammed with the introduction of a combo of TFs normally expressed in embryonic stem cells and these modified cells were able
to behave as pluripotent stem cells after reprogramming Corrected cells.
-Sickle cell disease and Hemophilia B- genetically altered cells used in methods to treat these two conditions
-Study of individual responses to drugs- aim to determine the factors that influence drug specificity, metabolism, and toxicity.
Pharmacogenetics
-ALL- childhood leukemia which is treated with 6-mercaptopurine (6-MP), a fraction of which is inactivated by the TPMT enzyme.
1/300 have a low activity TPMT prevents inactivation of 6-MP accumulation of 6MP toxic byproduct that inhibits DNA
replication.
-Detect low activity by simple genetic test and can be treated by reducing the concentration of 6MP given to patients with reduced
TPMT activity