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CYTOGENETICS > SINGLE GENE DISORDER > Flashcards

SINGLE GENE DISORDER Flashcards

1
Q

complete set of chromosomes but a problem in a single gene in a single chromosome

A

Single Gene Disorder

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2
Q

what are the modes of inheritance in single gene disorder?

A
  1. Autosomal Dominant
  2. Autosomal Recessive
  3. X-linked
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3
Q
  • Genetic disorders caused by genes on the autosomes in which a single abnormal allele is sufficient to cause disease despite the presence of normal alleles
A

Autosomal Dominant Diseases

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4
Q

how are genes inherited in autosomal dominant diseases?

A
  • randomly
  • 50-50% chance
  • can affect both sexes and can appear in every generation
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5
Q
  • autosomal dominant trait with complete penetrance
  • most common form of human genetic dwarfism
A

Achondroplasia

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6
Q

chromosome affected in achondroplasia

A

short arm of chromosome 4 (4p16)

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7
Q

gene affected in achondroplasia

A

FGFR3 - Fibroblast-Growth Factor Receptor Gene 3

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8
Q

main characteristic of Achondroplasia

A

Short-limbed dwarfism and macrocephaly

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9
Q

examples of autosomal dominant diseases

A
  • Achondroplasia
  • Charcot-Marie Tooth Disease
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10
Q
  • falls under the classification of diseases called Hereditary Motor and Sensory Neuropathies (HMSN) which causes motor and sensory neuropathies
  • most common autosomal dominant disorder in humans
A

Charcot-Marie Tooth Disease

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11
Q

chromosome affected in CMT disease

A

Short arm of Chromosome 17

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12
Q

gene affected in CMT disease

A

CMT Type 1A

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13
Q

abnormality of CMT Type 1A

A

producing excess Peripheral Myelin Protein

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14
Q

main characteristics of CMT disease

A
  • high arched feet
  • nerve demyelination
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15
Q

genetic disorders caused by genes on the autosomes in which the disorder is caused by having two disease-causing copies of a gene

A

Autosomal Recessive Diseases

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16
Q

how are genes inherited in autosomal recessive diseases?

A

an individual who has inherited 2 abnormal alleles at a given locus by receiving 1 mutant allele from each parent

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17
Q

if both parents are carriers of an autosomal recessive disease:

A
  • 25% chance with normal allele (normal)
  • 50% chance with only 1 abnormal allele (carrier)
  • 25% chance with 2 abnormal alleles (abnormal)
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18
Q

diseases under autosomal recessive

A
  • cystic fibrosis
  • hereditary hemochromatosis
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19
Q
  • most common fatal autosomal recessive disorder of Caucasian children
  • a multisystem disorder affecting the cells that produce mucus, sweat, saliva, and digestive juices
A

Cystic Fibrosis

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20
Q

chromosome affected in cystic fibrosis

A

long arm of chromosome 7

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21
Q

gene affected in cystic fibrosis

A

CFTR gene — Cystic Fibrosis Transmembrane Conductance Regulator Protein

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22
Q

person must have ? mutant CFTR allels to develop the disease

A

two

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23
Q

if CFTR does not function correctly:

A
  • CFTR channel won’t be able to move chloride thus resulting to no release of chloride leading to no attraction of water
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24
Q

signs and symptoms of cystic fibrosis

A
  1. Chronic lung infection
  2. Pancreatic insufficiency
  3. Respiratory failure
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25
Q

most serious complication for cystic fibrosis

A

respiratory failure

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26
Q
  • characterized by excessive deposition in healthy tissue
  • causes pancreas, liver, and skin damage as well as heart disease and diabetes
A

Hereditary Hemochromatosis

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27
Q

affected individuals absorb approximately ? of iron, as normal people would absorb approximately ? of iron

A

3-4 mg/day, 1-2mg/day

28
Q

chromosome affected in hereditary hemochromatosis

A

long arm of chromosome 6

29
Q

gene affected in hereditary hemochromatosis

A

Hemochromatosis type 1 gene (HFE)

30
Q

functions of HFE

A
  • regulated the amount of iron absorbed from food
  • but once mutated, it results in no regulation and constant absorption occurs
31
Q

early symptoms of hereditary hemochromatosis

A
  • weakness
  • lethargy
  • joint pains
  • abdominal pain
32
Q

treatment for hereditary hemochromatosis

A
  1. Phlebotomy
  2. Avoiding ferrous, mineral supplements, excess vitamin C, or uncooked seafood
33
Q

mutant allele resides on the X-chromosome

A

X-linked diseases

34
Q

carriers of x-linked diseases, with 1 normal and 1 mutant allele but typically not affected

A

Females

35
Q

receiving the mutant allele from their mothers, having only 1 X chromosome; thus always affected by X-linked chromosome

A

Males

36
Q

all daughters of affected males are ? of a mutant allele

A

carriers

37
Q

carrier female have: (chances)

A
  • 25% chance — normal allele son
  • 25% chance — affected son
  • 25% chance — carrier daughter
  • 25% chance — normal allele daughter
38
Q

x-linked mutation are almost always (dominant/recessive)

A

recessive

39
Q

genetic mutations transmitted from an affected father to daughters:

A
  • unaffected sons
  • carrier daughters
40
Q

genetic mutations transmitted from a carrier daughter to offspring

A
  • daughter’s son has a 50% chance of inheriting the mutation
  • daughter’s daughter has a 50% chance of being carriers
41
Q

genetic mutation is almost (always/never) transmited from an affected father to a son

A

never

42
Q

diseases under x-linked diseases

A
  • hemophilia A
  • duchenne muscular dystrophy
  • fragile X syndrome
43
Q
  • x-linked recessive bleeding disorder
A

Hemophilia A

44
Q

chromosome affected in hemophilia A

A

long arm of X chromosome band 28 (Xq28)

45
Q

gene affecting hemophilia A

A

Factor 8 (deficiency of Factor 8 Xq28)

46
Q
  • characterized by progressive skeletal muscle wasting
  • most common severe neuromuscular disease in humans
A

Duchenne Muscular Dystrophy

47
Q

onset of DMD

A

before 3 years old

48
Q

chromosome affected in DMD

A

short arm of chromosome X, band 21 (Xp21)

49
Q

Xp21 encodes the protein ?

A

Dystrophin

50
Q

functions of dystrophin

A
  • transfers the force of muscle contractions from inside muscle cells to outside cell membranes
  • resuting to ineffective growth and contraction of muscles leading to a series of manifestations, signs, and symptoms
51
Q

main characteristics of DMD

A
  • thick lower leg muscles (muscle is mostly fat and not strong)
  • tight heel cord (contracture) child may walk toes
  • weak muscles in front of leg cause “foot drop” and tip toe contractures
52
Q

one of the most common inherited form of mental retardation

A

Fragile X Syndrome

53
Q

Site of genetic disorder in fragile X

A

Chromosome X, long arm, band 27.3 (Xq27.3)

54
Q

cause of Fragile X syndrome

A
  • due to expansion of CGG repeats in 5’ untranslated region
  • hypermethylation of the CGG region leads to FMR1 gene silencing
55
Q

normal CGG repeats

A

6-45 repeats

56
Q

Intermediate CGG repeats (gray zone, little symptoms)

A

46-54

57
Q

pre-mutation CGG repeats

A

55-200; leads to ADHD or autism

58
Q

full mutation CGG repeats

A

more than 200 repeats; leads to hypermethylation

59
Q

characteristics of fragile X syndrome

A
  • shows a gap or break in the structure of the X chromosome
  • clinical feaatures worsen with each generation (anticipation)
  • affects only male
60
Q

main characteristics of Fragile X syndrome

A
  • broad forehead
  • elongated face
  • large everted earch
  • mitral valve prolapse
  • mental retardation
61
Q

20% cytologically and clinically normal but may transmit the disease to all his daughters and to affected grandchildren

A

carrier males

62
Q

brothers of transmitting males are at ?% risk of having mental retardation

A

9%

63
Q

grandsons of transmitting males have ?% risk

A

40%

64
Q

?% of carrier females are affected and are mentally retarded

A

50%

65
Q
  • rare
  • regulary expressed in heterozygotes (pedigree pattern is similar to autosomal dominant)
  • females can be affected
A

X-linked Dominant Diseases

66
Q

x-linked dominant disease affected males have: (offspring)

A

normal sons and abnormal daughters

67
Q

children (male and female) of carrier mothers have a ?% chance of inheriting x-linked dominant diseases

A

50%

CYTOGENETICS (11 decks)

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