GENETIC
DISORDERS
DISEASES
•GENETIC
•ENVIRONMENTAL
•BOTH
• CONGENITAL
• HEREDITARY
• FAMILAL
MUTATIONS
• PERMANENT change in DNA
• GENE MUTATION: (may, and often, result in a
single base error)
• CHROMOSOME MUTATION: (visible
chromosome change)part of chromosome
• Translocation
• inversions
• GENOME MUTATION: (whole chromosome)
Base pair triplet gene chromosome segment whole
chromosome genome
COMPLEX MULTIGENIC DISORDER
• Interaction btw varient forms of genes and
environmental factors
• Gene variation---polymorphism----multigenic
or polygenic( atherosclerosis, diabetes,
hypertension, ht &WT
• CONSTITUTIONAL germ cells
inherited disorder—in all cells
• SOMATIC → cancer
↘congenital malformation
in specific cells
• PENETRATION
GENE MUTATION
• DELETION OF A SINGLE BASE
• SUBSTITUTION OF A SINGLE BASE
• POINT MUTATION---WITHIN CODING
SEQUENCE--single base/different base--• Results with replacement of one amino acid
with another
1. Missence mutation
conservative
nonconservative
2.Nonsense mutation---AA change—stop
codon—Beta thal
POINT MUTATION
• MUTTIONS in NON-coding sequences
defective transcription, regulation, apop.
• DELETIONS/INSERTIONS 1.Multiple of three
• 2.Premature stop codon
• 3.“frameshift” mutation, involvement is NOT
a multiple of 3
• Tri-nucleotide REPEATS, e.g., CGG repeats
many times in fragile X syndrome, CAG in
others
SEQUENCE AND COPY NUMBER VARIATIONS
(POLYMORPHISMS)
• any two individuals share greater
• than 99.5% of their DNA sequences
• diversity of humans is encoded in less than
0.5% of our
• , this 0.5% represents about 15 million base
• pairs.
• two most common forms of DNA variations
Two most common forms of DNA variations
(polymorphisms) in the human genome are
1.Singlenucleotide polymorphisms (SNPs)
SNPs represent variation at single isolated
nucleotide
2.Copy number variations (CNVs).
• •
• positions and are almost always biallelic (i.e.,
one of only
• two choices exist at a given site within the
population,
• such as A or T). Much effort has been devoted
to making
• SNP maps of the human genome. These
efforts have
• identified over 6 million SNPs in the human
population,
• CNVs are a recently identified form of genetic
variation
• consisting of different numbers of large
contiguous
• stretches of DNA from 1000 base pairs to
millions of
• base pairs. In some instances these loci are,
like SNPs,
• biallelic and simply duplicated or deleted in a
subset of
Epigenetic Changes
• Epigenetic changes are those involving
modulation of gene or protein expression in
the absence of alterations in DNA sequence
(i.e., mutation)
• Epigenetic regulation is of critical importance
during development, as well as in homeostasis
of fully developed tissues.
• alterations in the methylation of cytosine
residues at gene promoters—heavily
methylated promoters become inaccessible to
RNA polymerase, leading to transcriptional
• silencing. Promoter methylation and silencing
of tumor suppressor genes leads to unchecked
cell growth –cancer
• Another major player in epigenetic are
• histone proteins, which are components of
structures called nucleosomes, around which
DNA is coiled.
• Histone proteins undergo a variety of
reversible modifications (e.g., methylation,
• acetylation) that affect secondary and tertiary
DNA structure, and hence gene
• Alterations in Non-Coding RNAs
• —so-called “non-coding RNAs (ncRNAs)”—
play important regulatory functions.
• Although many distinct families of ncRNAs
exist
• two imortant are microRNAs (miRNAs), and
long non-coding RNAs
• The miRNAs, unlike messenger RNAs, do
• not encode proteins but instead inhibit the
translation of target mRNAs into their
corresponding proteins. Posttranscriptional
• silencing of gene expression by miRNA is
preserved in all living forms from plants to
humans and is therefore a fundamental
mechanism of gene regulation
• In addition to alterations in DNA sequence,
coding genes also can undergo structural
variations, such as copy number changes
(amplifications or deletions), or translocations,
• resulting in aberrant gain or loss of protein
function. with mutations, Philadelphia
chromosome— translocation t(9;22) between
the BCR and ABL genes in
• chronic myelogenous leukemia
GENE MUTATIONS
•
•
•
•
•
INTERFERE with protein synthesis
SUPPRESS transcription, DNARNA
PRODUCE abnormal mRNA
DEFECTS carried over into TRANSLATION
ABNORMAL proteins WITHOUT
impairing syntheses
GENETIC DISORDERS
• SINGLE gene mutations, following
classical MENDELIAN inheritance
patterns the most
• MULTIFACTORIAL inheritance
• CHROMOSOMAL disorders
• NON-MENDELIAN disorders
MENDELIAN inheritance patterns
• AUTOSOMAL DOMINANT
• AUTOSOMAL RECESSIVE
• SEX-LINKED (recessive), involving
“X” chromosome
• • Suspected sex chromosome abnormality
(e.g., Turner syndrome)
• • Suspected fragile X syndrome
• • Infertility (to rule out sex chromosome
abnormality)
• • Multiple spontaneous abortions (to rule out
the parents as carriers of balanced
translocation;
AUTOSOMAL DOMINANT
• Disease is in HETEROZYGOTES
• NEITHER parent may have the disease (NEW mut.)
• REDUCED PENETRANCE (environment?,
other genes?)
• VARIABLE EXPRESSIVITY (environment?,
other genes?)
• May have a DELAYED ONSET
• Usually result in a REDUCED PRODUCTION
or INACTIVE protein
AUTOSOMAL DOMINANT
•
•
•
•
•
•
•
HUNTINGTON DISEASE
NEUROFIBROMATOSIS
MYOTONIC DYSTROPHY
TUBEROUS SCLEROSIS
POLYCYSTIC KIDNEY
HEREDITARY SPHEROCYTOSIS
VON WILLEBRAND DISEASE
•
•
•
•
•
•
MARFAN SYNDROME
EHLERS-DANLOS SYNDROMES (some)
OSTEOGENESIS IMPERFECTA
ACHONDROPLASIA
FAMILIAL HYPERCHOLESTEROLEMIA
ACUTE INTERMITTENT PORPHYRIA
AUTOSOMAL DOMINANT PEDIGREE
1) BOTH SEXES INVOLVED
2) GENERATIONS
NOT SKIPPED
AUTOSOMAL RECESSIVE
• Disease is in HOMOZYGOTES
• More UNIFORM expression than AD
• Often COMPLETE PENETRANCE
• Onset usually EARLY in life
• NEW mutations rarely detected clinically
• Proteins show LOSS of FUNCTION and
compensated in heterozygote form
• Include ALL inborn errors of metabolism
• MUCH more common that autosomal dominant
AUTOSOMAL RECESSIVE
•
•
•
•
•
•
•
•
•
CF
PKU
GALACTOSEMIA
HOMOCYSTINURIA
LYSOSOMAL STORAGE
Α-1 ANTITRYPSIN
WILSON DISEASE
HEMOCHROMATOSIS
GLYCOGEN STORAGE
DISEASES
Hgb S
THALASSEMIAS
CONG. ADRENAL HYPERPLASIA
EHLERS-DANLOS (some)
ALKAPTONURIA
NEUROGENIC MUSC. ATROPHIES
FRIEDREICH ATAXIA
SPINAL MUSCULAR ATROPHY
AUTOSOMAL RECESSIVE PEDIGREE
1) BOTH SEXES
INVOLVED
2) GENERATIONS
SKIPPED
SEX (“X”) LINKED
•
•
•
•
MALES ONLY
HIS SONS are OK, right?
ALL his DAUGHTERS are CARRIERS
The “Y” chromosome is NOT homologous to
the “X”, i.e., the classic concept of
dominant/recessive has no meaning here
• HETEROZYGOUS FEMALES have no
phenotypic expression (carriers)….usually,
this means autosomal “recessive”, right?
SEX (“X”) LINKED
•
•
•
•
•
•
•
•
DUCHENNE MUSCULAR DYSTROPHY
HEMOPHILIA , A and B
G6PD DEFICIENCY
AGAMMAGLOBULINEMIA
WISKOTT-ALDRICH SYNDROME
DIABETES INSIPIDUS
LESCH-NYHAN SYNDROME
FRAGILE-X SYNDROME
SEX LINKED PEDIGREE
1) MALES ONLY, sons of affected males are OK
2) GENERATION SKIPPING DOESN’T MATTER
SINGLE GENE DISORDERS
• ENZYME DEFECT (Most of them, e.g., PKU)
– Accumulation of substrate
– Lack of product
– Failure to inactivate a protein which causes damage
• RECEPTOR/TRANSPORT PROTEIN DEFECT (Familial
Hypercholesterolemia)
• STRUCTURAL PROTEIN DEFECT (Marfan, Ehl-Dan)
– Structure
– Function
– Quantity
• ENZYME DEFECT WHICH INCREASES DRUG
SUSCEPTIBILITY: G6PDPrimaquine
STRUCTURAL PROTEIN DEFECTS
• Marfan Syndrome
– Fibrillin-1 defect (not -2 or -3)
– Tall, dislocated lens, aortic arch aneurysms, etc.
– Abraham Lincoln?, Osama bin-Laden?
• Ehlers-Danlos Syndromes (AD, AR)
– Multiple (6?) different types
– Classical, Hypermob., Vasc., KyphoSc., ArthChal., Derm
– Various collagen defects
– Hyperelastic skin, hyperextensible joints
RECEPTOR PROTEIN DEFECTS
• FAMILIAL HYPERCHOLESTEROLEMIA
– LDL RECEPTOR defect
– Cholesterol TRANSPORT across liver cell impaired
– ergo, CHOLESTEROL BUILDUP IN BLOOD
• “Scavenger System” for CHOL kicks in, i.e.,
MACROPHAGES
• YOU NOW KNOW THE REST OF THE STORY
• YOU NOW KNOW WHY MACROPHAGES are
“FOAMY”
ENZYME DEFICIENCIES
• BY FAR, THE LARGEST KNOWN
CATEGORY
– SUBSTRATE BUILDUP
– PRODUCT LACK
– SUBSTRATE could be HARMFUL
• LYSOSOMAL STORAGE DISEASES
comprise MOST of them
LYSOSOMAL STORAGE DISEASES
•
•
•
•
•
•
GLYCOGEN STORAGE DISEASES
SPHINGOLIPIDOSES (Gangliosides)
SULFATIDOSES
MUCOPOLYSACCHARIDOSES
MUCOLIPIDOSES
OTHER
– Fucosidosis, Mannosidosis, Aspartylglycosaminuria
– WOLMAN, Acid phosphate deficiency
GLYCOGEN STORAGE DISEASES
• MANY TYPES (at least 13)
• Type 2 Pompe (acid-α-glucosidase) , von Gierke
(Glu-6P-ase), McArdle (phosphorylase), most
studied and discussed, and referred to
• Storage sites: Liver, Striated Muscle (Skel + Ht)
SPHINGOLIPIDOSES
• MANY types, Tay-Sachs most often referred to
–
–
–
–
–
GANGLIOSIDES are ACCUMULATED
Ashkenazi Jews (1/30 are carriers)
CNS neurons a site of accumulation
CHERRY RED spot in Macula
Usually fatal by age 4
SULFATIDOSES
• MANY types, but the metachromatic
leukodystrophies (CNS), Krabbe, Fabry,
Gaucher, and Niemann-Pick (A and B) are
most commonly referred to
• SULFATIDES, CEREBROSIDES,
SPHINGOMYELIN are the accumulations
•
•
•
•
•
•
NIEMANN-PICK
TYPES A, B, C
SPHINGOMYELIN BUILDUP
Sphingomyelinase (ASM), is the missing enzyme
MASSIVE SPLENOMEGALY
ALSO in ASHKANAZI JEWS
OFTEN FATAL in EARLY LIFE, CNS, ORGANOMEGALY
GAUCHER DISEASE
• GLUCOCEREBROSIDE BUILDUP
• 99% are type I, NO CNS involvement
• ALL MACROPHAGES, liv, spl, nodes, marrow
MUCOPOLYSACCHARIDOSES
• HURLER/HUNTER, for I and II, respectively, 14
types
• DERMATAN sulfate, HEPARAN sulfate buildup,
respectively
– coarse facial features
– clouding of the cornea
– joint stiffness
– mental retardation
– URINARY EXCRETION of SULFATES COMMON
OTHER LYSOSOMAL STORAGE DIS.
•
•
•
•
•
FUCOSIDOSIS
MANNOSIDOSIS
ASPARTYLGLYCOSAMINURIA
WOLMAN (CHOL., TRIGLYCERIDES)
ACID PHOSPHATE DEFICIENCY (PHOS. ESTERS)
ALCAPTONURIA
•
•
•
•
NOT a LYSOSOMAL ENZYME DISEASE
FIRST ONE TO BE DESCRIBED
HOMOGENTISIC ACID
HOMOGENTISIC ACID OXIDASE
–BLACK URINE
–BLACK NAILS (OCHRONOSIS), SKIN
–BLACK JOINT CARTILAGE (SEVERE ARTHRITIS)
NEUROFIBROMATOSIS
• 1 and 2
– 1-von Recklinghausen
– 2- “acoustic” neurofibromatosis
• 1
– Neurofibromas, café-au-lait, Lisch nodules
NEUROFIBROMATOSIS
• 1 and 2
• 1-von Recklinghausen
• 2- “acoustic” neurofibromatosis
• 2
– Bilateral acoustic neuromas and multiple meningiomas
MULTIFACTORIAL INHERITANCE
• Multi-”FACTORIAL”, not just multi-GENIC
• “SOIL” theory
• Common phenotypic expressions governed by
“multifactorial” inheritance
– Hair color
– Eye color
– Skin color
– Height
– Intelligence
– Diabetes, type II
FEATURES of
multifactorial inheritance
•
•
•
•
Expression determined by NUMBER of genes
Overall 5% chance of 1st degree relatives having it
Identical twins >>>5%, but WAY less than 100%
This 5% is increased if more children have it
• Expression of CONTINUOUS traits (e.g.,
height) vs. DISCONTINUOUS traits (e.g., diabetes)
“MULTIFACTORIAL” DISORDERS
•
•
•
•
•
•
•
•
Cleft lip, palate
Congenital heart disease
Coronary heart disease
Hypertension
Gout
Diabetes
Pyloric stenosis
MANY, MANY, MANY, MANY MORE…..
•
•
•
•
KARYOTYPING
Defined as the study of CHROMOSOMES
46 = (22x2) + X + Y
Conventional notation is “46,XY” or “46,XX”
G(iemsa)-banding, 500 bands per haploid
recognizable
• Short (“p”-etit) arm = p, other (long) arm = q
More KARYOTYPING info
• A,B,C,D,E,F,G depends on chromosome length
– A longest
– G shortest
• Groups within these letters depend on the p/q
ratio
• ARMREGIONBANDSub-BAND,
numbering from the centromere progressing
distad
F.I.S.H.
(gene “probes”)
greatly enhances G-banding
• Fluorescent InSitu
Hybridization
• Uses fluorescent
labelled DNA
fragments, ~10,000
base pairs, to bind (or
not bind) to its
complement
FISH
• SUBTLE MICRODELETIONS
• COMPLEX TRANSLOCATIONS
• AND TELOMERE ALTERATIONS
TRIPLE CHROMOSOME #20
A DELETION in
CHROMOSOME #22
SPECTRAL KARYOTYPING
CYTOGENETIC DISORDERS
• DEFINITIONS:
–EUPLOID (46XX or 46XY)
–ANEUPLOID (NOT AN EXACT MULTIPLE
OF 23)
• MONOSOMY, AUTOSOME OR SEX
• TRISOMY, AUTOSOME OR SEX
–DELETION
–BREAKAGE
MORE DEFINITIONS
COMMON CYTOGENETIC DISEASES
• AUTOSOMES
– TRISOMY-21 (DOWN SYNDROME)
– 8, 9, 13 (Patau), 18 (Edwards), 22
– 22q.11.2 deletion
• SEX CHROMOSOMES
–KLINEFELTER: XXY, XXXY, etc.
–TURNER: XO
TRISOMY-21
TRISOMY-21
• Most trisomies (monosomies, aneuploidy) are
from maternal non-disjunction
• (non-disjunction or anaphase lag are BOTH
possible)
• #1 cause of mental retardation
• Maternal age related
• Congenital Heart Defects, risk for acute leukemias,
GI atresias
• Most LOVABLE of all God’s children
Chromosome 22q11.2
Deletion Syndrome
• Because of a DELETION, this cannot be
detected by standard karyotyping and
needs FISH
• Cardiac defects, DiGeorge syndrome,
velocardiofacial, CATCH*
SEX CHROMOSOME DISORDERS
• Problems related to sexual development and
fertility
• Discovered at time of puberty
• Retardation related to the number of X
chromosomes
• If you have at least ONE “Y” chromosome,
you are male
KLINEFELTER (XXY, XXXY, etc.)
• Hypogonadism found at puberty
• #1 cause of male infertility
• NO retardation unless more X’s
• 47, XXY 82% of the time
• L----O----N----G legs, atrophic testes,
small penis
TURNER (XO)
• 45, X is the “proper” designation
• Mosaics common
• Often, the WHOLE chromosome is not
missing, but just part
• NECK “WEBBING”
• EDEMA of HAND DORSUM
• CONGENITAL HEART DEFECTS most
FEARED
• “STREAK” OVARIES
HERMAPHRODITES
♂
♀
• GENETIC SEX is determined by the PRESENCE or ABSENCE
of a “Y” chromosome, but there is also, GONADAL
(phenotypic), and DUCTAL sex
• TRUE HERMAPHRODITE: OVARIES AND TESTES, often on
opposite sides (VERY RARE)
• PSEUDO-HERMAPHRODITE:
– MALE: TESTES with female characteristics (Y-)
– FEMALE: OVARIES with male characteristics (XX)
SINGLE GENE, NON-Mendelian
• Triplet repeats
–Fragile X (CGG)
–Others: ataxias, myotonic dystrophy
• Mitochondrial Mutations: (maternal)
(LEBER HEREDITARY OPTIC NEUROPATHY)
• Genomic “IMPRINTING”: (Inactivation of
maternal or paternal allele, contradicts Mendel)
• Gonadal “MOSAICISM”: (only gametes have
mutated cells)
MOLECULAR DX by DNA PROBES
•
•
•
•
•
•
•
BIRTH DEFECTS, PRE- or POST- NATAL
TUMOR CELLS
CLASSIFICATIONS of TUMORS
IDENTIFICATION of PATHOGENS
DONOR COMPATIBILITY
PATERNITY
FORENSIC
H&E tissue
structures
ImmunoAntigen
Proteins
GENES that
MAKE those
PROTEINS
METHODS OF DNA ANALYSIS
Fluorescence in Situ Hybridization (FISH)
• FISH utilizes DNA probes that recognize
sequences specific to chromosomal regions of
greater than 100 kilobases in size, which
defines the limit of resolution with this
technique for identifying chromosomal
changes.
• Such probes are labeled with fluorescent dyes
and applied to metaphase spreads or
interphase nuclei.
• The probe hybridizes to its complementary
sequence on the chromosome and thus
• labels the specific chromosomal region that
can then be visualized under a fluorescence
microscope.
Array-Based Genomic Hybridization
• FISH requires previous knowledge of the one
or few specific chromosomal regions
However, chromosomal abnormalities may
also be detected without previous knowledge
global strategy known as array based CGH.
• Test DNA and a reference (normal) DNA are
labeled with two different fluorescent dyes (
Cy5 and Cy3, which fluoresce red and green, ).
The differentially labeled samples are then
• hybridized to an array of segments of genomic
• Amplifications and deletions in the test
sample produce an increase or decrease in
signal relative to the normal DNA that can be
detected down to a 10-kilobase (kb)
resolution
• Newer generations of microarrays using
• single-nucleotide polymorphisms (SNPs)
provide even higher resolution
Polymerase Chain Reaction (PCR)
Analysis
• Direct Detection of DNA Mutations by
Polymerase Chain Reaction (PCR) Analysis PCR
analysis, which involves exponential
amplification of DNA, is now widely used in
molecular diagnosis.
• If RNA is used as the substrate, it is first
reverse-transcribed to obtain cDNA and then
amplified by PCR. This method involving
reverse transcription (RT) often is abbreviated
as RT-PCR.
• One prerequisite for direct detection is that
the sequence of the normal gene must be
known. To detect the mutant gene, two
primers that bind to the 3′ and 5′ ends of
• the normal sequence are designed. By utilizing
appropriate DNA polymerases and thermal
cycling, the target DNA is greatly amplified,
producing millions of copies of the DNA
Linkage Analysis and GenomeWide Association Studies
• Direct diagnosis of mutations is possible only
if the gene responsible for a genetic disorder
is known and its sequence has been identified.
In several diseases that have a genetic
• basis, including some common disorders,
direct genetic diagnosis is not possible, either
because the causal gene has not been
identified or because the disease is
multifactorial (polygenic) and no single gene
is involved.
• Two types of analyses can be performed for
unbiased identification of disease-associated
gene(s):
• linkage analysis
• genome-wide association studies (GWASs).
In both surrogate markers in the genome,
marker loci, must be used to localize the
chromosomal regions of interest, based on
their linkage to one regions
• Prenatal genetic analysis should be offered to
all patients who are at risk of having
cytogenetically abnormal progeny.
• It can be performed on cells obtained by
amniocentesis, on chorionic villus biopsy
material, or on umbilical cord blood .
Indications are the following:
Advanced maternal age (beyond 34
Years),which is associated with greater risk of
trisomies
Confirmed carrier status for a balanced
reciprocal translocation, Robertsonian
translocation, or inversion (inPrenatal genetic
analysis should be offered to all patients
• • A chromosomal abnormality affecting a
previous child
• • Determination of fetal sex when the patient
or partner is a confirmed carrier of an X-linked
genetic disorder
• Postnatal genetic analysis usually is performed
on peripheral blood lymphocytes.
• • Multiple congenital anomalies
• • Unexplained mental retardation and/or
developmental delay
• • Suspected aneuploidy (e.g., features of
Down syndrome)
• • Suspected unbalanced autosome (e.g.,
Prader-Willi syndrome)