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Genetic Diseases
Amrik Sahota
Dept Path & Lab Med
UMDNJ - RWJMS
sahotaam@umdnj.edu
1
Basic Pathology (8 th ed)
Ch 7, 60 pages
Online version, excluding figures
90 minutes to present
Less than 2 min per page
Not all topics covered
2
What’s the Nature of This Talk?
Review
Go over a subject again to fix it in memory
Critical evaluation of a subject
Preview
Glimpse of things to come
Advance showing before public opening
Overview
General outline of a subject
Survey or summary
3
Major Topics
Mutations
Single gene disorders
Chromosomal disorders
Multifactorial disorders
Molecular diagnostics
Pediatric disorders (not discussed)
4
Mutation
A change in DNA sequence that may lead to a
change in phenotype
Change is permanent but can be dynamic
Can occur in germline or somatic cells
Germline mutations can be transmitted from one
generation to the next
Somatic mutations important in cancer
Important to distinguish mutation from
polymorphism
5
Polymorphic Markers
Marker # Loci Comment
Chromosomes Structural changes
Blood groups ~ 20 May need fresh blood
Serum proteins ~30 May need fresh serum
HLA antigens 1 Linkage to chr. 6p only
DNA RFLPs >105 Two allele markers
DNA minisatt. >104 Many alleles, highly informative
DNA microsatt. >105 Many alleles, highly informative
DNA SNPs >4x106 Less informative; easy to type
6
Microsatellite markers
7
Single Nucleotide
Polymorphisms
Strachan
and Read,
2004
8
Causes of Mutation
Spontaneous mutations
Arise naturally during DNA
replication
Induced mutations
Ionizing radiation (X-rays)
Non-ionizing radiation (UV)
Chemical mutagens
9
Types of Mutation
Single gene mutations
Minor structural alterations (single base
changes, deletions, insertions, etc)
Chromosomal mutations
Major structural alterations (deletions,
insertions, inversions, translocations, etc)
Loss or gain of whole chromosomes
(monosomies, trisomies, etc)
10
Single Gene Mutations
Structural gene mutations
Minor base pair changes
Deletions or insertions
Gene duplications
Regulatory region mutations
Promoter region
Splice site mutations
Dynamic mutations
Trinucleotide repeat expansions
11
Point Mutation (Sickle Cell)
12
Single Base Deletion (ABO)
13
Three-base Deletion (Cystic Fibrosis)
14
Premature Chain Termination
(Beta Thalassemia)
15
Four-base Insertion in Hexosaminidase
A Gene (Tay-Sachs)
16
Summary of Single Gene Mutations
Type Effect Example
Deletion Null Cystic fibrosis
Insertion Null Tay-Sachs
Inversion Null Hemophilia A
Missense Null Sickle cell
Nonsense Null Beta-globin
Frameshift Null Cystic fibrosis
Splicing Null Beta-globin
Regulatory Low exp. Beta-globin
17
Molecular Consequences of
Single Gene Mutations
Loss of function
Metabolic enzymes
Haploinsufficiency
Receptor mutations
Dominant negative mutation
Genes for multimeric proteins
Gain of function
Completely novel protein
18
Loss of Function Mutations
From Genomes (2002)
19
Adenine Phosphoribosyltransferase
(APRT) Deficiency
APRT
Adenine X AMP
XDH
DHA
Precipitation/crystallization
Crystals in kidney
Aggregation
Stones in kidney
Blockage of tubules
Renal injury
Tubular loss
Renal failure
20
APRT Mutations
E4-wild: C C A C T G G T G G T A A G G G T C T C C C C G
T Insertion
E4-mutant: C C A C T G G T G G T T A A G G G T C T C C C C
Recognition Sequence by Tru9I
Recognition Sequence by Mbo
II
E5-wild: C T G T A C C C T T C T T C T C T C T C C T G C A
TCT Deletion
E5-mutant: CT GTAC C CTT CT CT CT C CT G CAGTA
21
Haploinsufficiency
A single copy of the normal gene is incapable of
providing sufficient protein to assure normal
function
Individuals heterozygous for the mutation are
clinically affected
Familial hypercholesterolemia (FH) well known
example
From GeneTests
22
FH and LDL receptor
23
LDL Receptor Mutations
24
Dominant-negative Mutations
• A mutation whose gene product adversely
affects the normal,wild-type gene product within
the same cell, usually by dimerizing (combining)
with it.
• For polymeric molecules, such as collagen,
dominant negative mutations are often more
deleterious than mutations causing the
production of no gene product (null mutations).
• From GeneTests
25
Dominant-negative Mutations: Collagen Genes
26
Gain of Function Mutation
A mutation that confers new or enhanced activity
on a protein
Loss of function mutations, which are more
common, result in reduced or abolished protein
function
From MedicineNet.com
27
Gain of Function Mutation: Oncogenes
28
Chromosomal Mutations
Deletion: Loss of a piece of a chromosome
Translocation: Breakage of two chromosomes and
fusion of broken parts
Isochromosome: Loss of one arm and duplication
of the other
Aneuploidy: Gain or loss of one or more intact
chromosomes
Mosaicism: More than one chromosomal
complement in a given individual
29
Chromosomal Mutations
30
Normal Male Karyotype
31
Types of Genetic Disorders
Single gene disorders
Mendelian; mitochondrial; triplet repeats;
imprinting; mosaicism
Chromosomal disorders
Major structural alterations; genomic changes
Multifactorial disorders
Multiple genes each with a small effect;
phenotype affected by environment
32
Single Gene Disorders
Thalassemia 1/50
HNPCC 1/200 to 1/1000
Sickle cell 1/400 to 1/600
Cystic fibrosis 1/2,000 to 1/4,000
Marfan syndrome 1/10,000 to 1/20,000
Jorde LB et al (1999), Medical Genetics (2nd ed)
33
Inheritance Patterns For Single
Gene Disorders
Classic
Autosomal dominant
Autosomal recessive
X-linked
Non-classic
Mitochondrial
Triplet repeat expansions
34
Autosomal Dominant Inheritance
Disorder occurs in individuals heterozygous
for a mutant gene
Disorder passed on from one generation to
next in a vertical manner
Both males and females affected, and can
pass on the trait with equal probability
Each affected individual has one affected
parent, except in case of a new mutation
35
Autosomal Dominant Inheritance
36
Autosomal Recessive Inheritance
Disorder occurs in individuals homozygous
for a mutant gene
Tends to be limited to a single sibship
(horizontal transmission)
Not found in multiple generations
Males and females affected with equal
probability
37
Autosomal Recessive Inheritance
(Congenital Deafness)
38
X-linked Inheritance
Caused by mutant genes on the X-
chromosome and expressed in males
Each son has a 50% chance of receiving the
mutant gene from the mother
Daughters also have a 50% chance, but will
also inherit a normal X from the father
Variable phenotype in carrier daughters,
because of random X inactivation
39
X-linked Inheritance (DMD)
40
Mitochondrial Disorders
Disturbances in oxidative phosphorylation
(OXPHOS) system
Includes nuclear and mitochondrial genes
Variable phenotype; affect many organs
1/10,000 live births
Leigh syndrome - progressive
encephalopathy - most common disorder
41
Mitochondrial Inheritance
Maternal inheritance
Multiple copies of mt DNA per cell
(polyplasmy)
Mutant and wild type mt DNA in each cell
(heteroplasmy)
Threshold effect – critical number of mutant
mt DNA required for disease phenotype
42
Mitochondrial Inheritance (Leber
Optic Neuropathy)
43
Other Disorders
Triplet repeat expansions
Germline and somatic instability
Earlier age of onset in subsequent
generations
Parental origin of disease allele affects
phenotype
E.g., Fragile X syndrome
44
Fragile X Syndrome
Most common cause of familial MR
Fragile site (FRAXA) at Xq27.3
20% of males clinically normal
1/3 of carrier females have variable MR
First example of trinucleotide repeat
mutations (expansions)
Expansion occurs during female meiosis
45
Fragile X Chromosome
46
Fragile X Pedigree
47
Nucleotide Repeat Mutations
48
Pathology of Single Gene Disorders
Sickle cell disease as an example
49
Sickle Cell Mutation
From Robbins (2005) 50
Sickle Cell Mutation
51
Harvard Med Sch 52
Normal and Sickle Cell Hemoglobin
Sickle cell
website
53
ORGAN/TISSUE PROBLEMS
INVOLVED CAUSED
KIDNEY Hematuria
Urinary frequency
SPLEEN Serious infections
Abdominal pain
LUNGS Pneumonia
Chest problems
BONES Infection
Necrosis
BRAIN Stroke
Headache
LIVER Hepatomegaly
Jaundice 54
Complications of Sickle Cell Disease
NCBI
bookshelf
55
Chromosomal Disorders
Down syndrome 1/700 to 1/1,000
Edward syndrome 1/5,000
Klinefelter syndrome 1/1,000 males
Turner syndrome 1/5,000 to
1/10,000 females
Jorde LB et al (1999), Medical Genetics (2nd ed)
56
Normal Male Karyotype
57
X Chromosome Idiogram
58
Finding Our Way Around
Geographic map Genetic map
Country Karyotype (23 chr)
State Chromosome (1)
North/South q arm/p arm
City Region (q1)
Neighborhood Band (q11)
Intersection Sub-band (q11.1)
Street Sub-sub-band (q11.11)
House Gene(s) 59
Philadelphia Chromosome in CML
Ph+
60
BCR-ABL Translocation in CML
61
BCR-ABL Gene Fusion
62
Down Syndrome (Trisomy 21)
63
Turner Syndrome (monosomy, 45,X)
64
Metaphase Fish (Trisomy 22)
65
Interphase FISH (Trisomy 20)
66
Common Multifactorial
Disorders
Congenital malformations
Cleft lip/palate, congenital heart defects,
Common adult diseases
Alcoholism, diabetes (I and II)
Quantitative traits
High blood pressure, obesity
67
Frequency of Multifactorial
Disorders
Cancer (all types) 1/3
Heart disease/stroke 1/3 to 1/5
Diabetes (Types I and II) 1/10
Alcoholism 1/10 to 1/20
Congenital heart defects 1/200 to 1/500
Neural tube defects 1/200 to 1/1,000
Jorde LB et al (1999), Medical Genetics (2nd ed)
68
Multifactorial Versus Single
Gene Disorders
“Run in families”, hence have a strong genetic
component but complex mode of inheritance
Individual genes underlying a multifactorial trait
follow Mendelian patterns of inheritance
Many of these genes act together to influence
disease phenotype
May have to exceed a threshold before expression
of disease phenotype
69
Comparison of Single Gene and
Multifactorial Diseases
Single gene disorder Multifactorial disease
Major effect of a single gene; Expression influenced by
may or may not require multiple genes and
environmental influence environment
Modifying genes affect Pronounced effect of modifier
phenotype to some extent genes
Easier to discern relationship Relation between genes and
between gene and phenotype phenotypes hard to discern
Phenotype due to mutations Polymorphisms determine
(recent origin) phenotype (ancient origin)
Usually early onset Usually late onset 70
Multifactorial Versus Polygenic
Diseases
Multifactorial:
Diseases or traits resulting from the interplay of
multiple environmental factors with multiple
genes.
Polygenic:
Diseases or traits resulting from the interaction
of multiple genes, each with a relatively minor
effect.
71
Interactions Between Genes and
Environment
Strachan
and Read,
2004
72
Molecular Diagnostics
Direct Testing
DNA testing (DNA, RNA)
Cytogenetic testing (chromosomes)
Biochemical testing (proteins,
metabolites)
Indirect Testing
Linkage analysis (co-inheritance of
markers)
73
Direct Gene Diagnosis (Factor V)
74
Allele Specific Oligo Probes
75
Fragile X Analysis
76
Summary
Mutations
Single gene disorders
Chromosomal disorders
Multifactorial disorders
Molecular diagnostics
77
Genetic Disorders: Here and Now
From GeneClinics 78
Era of Genetic Medicine
Most chronic diseases have a strong genetic-
environment interaction
Advances in human genetics - genetic medicine -
is having a profound effect on medical practice
Genetic medicine studies an individual’s genetic
variation, not a disease or its symptoms
Genetic medicine has turned the concept of
conventional medicine inside out
Genetic variation can be used to predict
susceptibility to chronic human diseases
79
