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Pathology > Chapter 5- Genetic Disorders > Flashcards

Chapter 5- Genetic Disorders Flashcards

1
Q

What types of mutations are highly penetrant and follow classic Mendelian inheritance patterns?

A

Single genes with large effects

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2
Q

What are the most common cause of genetic disorders?

A

Multi-genetic disorders

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3
Q

What is a mutation?

A

Permanent change in DNA

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4
Q

What is the difference between a germ cell and somatic mutation?

A

Germ cell- transmitted to offspring

Somatic- not transmissible

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5
Q

What kind of mutations are there?

A
  1. Coding
  2. Non-coding- enhancer or promoter
  3. Frameshift
  4. Trinucleotide repeat- amplification of triplet nt sequences
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6
Q

What are the two kinds of point mutations?

A
  1. Missense- single nt substitution changes the triplet base code
  2. Nonsense- single nt substitution creates a stop codon
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7
Q

What are the two types of missense mutations?

A
  1. Conservative- protein structure remains

2. Nonconservative- change affects the final protein structure

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8
Q

What is penetrance?

A

The percentage of individuals that carry the gene AND express the trait

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9
Q

What is variable expressivity?

A

Variation in the effect caused by the mutation (expression varies among individuals)

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10
Q

What is pleiotropism?

A

Multiple possible end effects of a single mutation (expressions within a person varies)

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11
Q

What is genetic heterogeneity?

A

Multiple different mutations can lead to the same outcome

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12
Q

What are the different transmission patterns of single gene disorders?

A
  1. Autosomal dominant- LOF
  2. Autosomal recessive- complete penetrance, metabolism errors
  3. X-linked- sex linked recessive, fully expressed in men
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13
Q

What are the consequences of enzyme defects?

A

Reduced synthesis

Toxic substrate accumulation

Decreased end product

Decreased substrate metabolism

Defects in receptors and transport

Alterations in non-enzyme proteins

Adverse drug reactions

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14
Q

What disorders are associated with structural proteins?

A

Marfan syndrome

Ehlers-Danlos syndrome

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15
Q

What are the characteristics of Marfan syndrome?

A

Mutation in 15q21.1 (fibrillin-1 gene)

Affects skeletal, ocular, CV and integumentary systems

Tall, long extremities, scoliosis

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16
Q

What are the characteristics of Ehlers-Danilo’s syndrome?

A

Defect in collagen synthesis

Fragile skin and poor wound healing

Hyper mobile joints

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17
Q

What are the characteristics of familial hypercholesterolemia?

A

Mutation in LDL receptor

Loss of feedback control (increased circulating cholesterol)

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18
Q

What disorders are associated with enzyme defects?

A

Lysosomal storage diseases

Tay-Sachs disease

Niemann-Pick

Gaucher disease

Mucopolysaccharidoses

Glycogen storage diseases

Allaptonuria/ochronosis

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19
Q

What are the characteristics of lysosomal storage diseases?

A

Accumulation of partially degraded metabolites

Enlarged lysosomes

Lack of autophagy

20
Q

What are the characteristics of Tay-Sachs disease?

A

Hexosaminidase deficiency inhibits ganglioside catabolism

Neurons most affected

Oil red O and Sudan black pos

Whorled lysosome

Cherry red spot in macula

21
Q

What are the characteristics of Neimann-Pick disease?

A

A (infantile) and B- sphingomyelin accumulation

C- defect in nonenzymatic lipid transport

22
Q

What are the characteristics of Gaucher disease?

A

Reduced glucocerebrosidase activity (accumulation)

PAS pos

23
Q

What are the different types of Gaucher disease?

A

I- mononuclear phagocyte involvement

II- CNS involvement, infants

III- involves both macrophages and CNS

24
Q

What are the characteristics of mucopolysaccharidoses?

A

Deficiency in enzymes that degrade glycosaminoglycans

Coarse facial features, mental retardation, corneal clouding valve and sub-endothelial arterial thickening

25
Q

What are the two forms of mucopolysaccharidoses?

A

Hunter- x-linked recessive

Hurler

26
Q

What are the three forms of glycogen storage diseases?

A
  1. Hepatic- catabolism deficiency
  2. Myopathic- glycolysis enzyme deficiency
  3. Miscellaneous- alpha-glucosidase deficiency, glycogen overload in many organs (Pompe=cardiac involvement)
27
Q

What are the characteristics of alkaptonuria/ochronosis?

A

Decreased homohentisic oxidase

Blocks phenylalanine metabolism

Homogentisic acid accumulation

Blue-black pigment

28
Q

What are polymorphisms?

A

Genes with at least two alleles (one has a frequency >1%)

29
Q

What are the numerical chromosomal disorders?

A

Monosomy

Trisomy

Mosaicism- different cell populations

30
Q

What are the structural chromosomal disorders?

A

Deletions

Translocation- balanced/reciprocal or Robertsonian/centric

Isochromsome- deletion and duplication

Inversion- paracentric or pericentric

Ring chromosome

31
Q

What are the different types of cytogenic autosomal disorders?

A

Trisomy 21 (Down syndrome)

Trisomy 18 (Edward’s syndrome)

Trisomy 13 (Patau syndrome)

Chromosome 22q11.2 deletion syndrome (diGeorge and velocardiofacial)

Cri du chat (5p deletion)

32
Q

What are the characteristics of Down syndrome?

A

Extra chromosome 21

Due to maternal age or Robertsonian translocation

Flat face, epicanthic folds, congenital heart disease

33
Q

What are the characteristics of Edward’s syndrome?

A

Extra chromosome 18

Mental retardation

Micrognathia, overlapping fingers, congenital heart defects, renal malformation

34
Q

What are the characteristics of Patau syndrome?

A

Extra chromosome 13

Microcephaly, mental retardation

Microphthalmia, polydactyly, cleft palate, cardiac and renal defects

35
Q

What are the two forms of chromosome 22q11.2 deletion syndrome and their characteristics?

A

DiGeorge- thumping hypoplasia, T cell deficiency

Velocardiofacial- congenital heart disease

36
Q

What is the Lyon hypothesis?

A

One x-chromosome is randomly selected to be inactivated

Mosaicism seen in females

37
Q

What is a Barr body?

A

Inactive X-chromosome

38
Q

What is SYR?

A

Sex determining region on a Y chromosome

39
Q

What are the cytogenetic disorders involving sex chromosomes?

A

Klinefelter syndrome (2+X and 1+Y)

Turner syndrome (monosomy of X)

40
Q

What are the three different types of trinucleotide repeat mutations?

A

Fragile X- CCG repeats during oogenesis

Huntington disease- CAG repeats during spermatogenesis

Friedreich’s ataxia- GAA repeats in FXN gene (LOF)

41
Q

Why is the expression of mutations in mitochondrial genes unpredictable?

A

Cell can contain both normal and mutant mtDNA

Heteroplasmy- proportions during division are random

42
Q

What is genomic imprinting?

A

Epigenetic process resulting in differential inactivation of either maternal or paternal alleles if certain genes

43
Q

What are the two disorders of genomic imprinting?

A
  1. Prader Willi- q12 deletion in chromosome 15 from father

2. Angelman- q12 deletion in chromosome 15 from mother

44
Q

How does gene silencing occur?

A

Methylation

45
Q

What is gonadal mosaicism?

A

Mutation in gonadal cells early in embryonic development

Disease can be passed on

Pathology (25 decks)

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