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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