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Genetics > Trinucleotide Repeat Disorders > Flashcards

Trinucleotide Repeat Disorders Flashcards

1
Q

What is trinucleotide repeat disorder?

A

abnormal number of expansion of a repetitive sequence of nucleotides

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2
Q

How many nucleotides do repeat in the repetitive sequence?

A

3 (three)

Hence, it is called ‘trinucleotide repeat disorder’

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3
Q

What is anticipation?

A

Earlier age on onset in successive generations + high severity of symptoms (in most cases)

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4
Q

Anticipation is seen characteristically in which group of genetic disorders?

A

Trinucleotide repeat disorders

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5
Q

What is the underlying mechanism of anticipation?

A

expansions are unstable >>> may enlarge in repeat number >>> earlier age of onset + more severe symptoms

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6
Q

Which body system is commonly involved in trinucleotide repeat disorders?

A

Nervous system

dominance of neurological disorders

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7
Q

What is the mnemonic for trinucleotide repeat disorders?

A

Hunt a Fragile X & Fry Muscle Spine Dentin

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8
Q

What are the trinucleotide (Triplet) repeat disorders?

A

Hunt = Huntington’s disease

Fragile X = Fragile X syndrome

Fry = Friedreich’s ataxia

Muscle = Myotonic dystrophy (Dystrophia myotonica)

Spine = Spinocerebellar ataxia

Spinobulbar muscular atrophy (= Bulbospinal neuropathy)

Dentine = Dentatorubral pallidolusian atrophy

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9
Q

What is the sequence of repeated triplets in Huntingoton’s disease?

A

CAG

Recall: Hunt & CAGe

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10
Q

What is the sequence of repeated triplets in Fragile X disease?

A

CGG

Recall: See (C) a Gross Guy

(Gross guy because Fragile x has large ears, jaw, testis)

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11
Q

What is the sequence of repeated triplets in Myotonic dystrophy?

A

CTG

Recall: See (C) Tonic Gestures

(Myotonic dystrophy has tonic gestures)

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12
Q

What is the sequence of repeated triplets in Friedreich’s Ataxia?

A

GAA

Recall: Go AtAxic

(Friedreich’s ataxia has inherited ataxia)

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13
Q

What is another name of spinobulbar muscular atrophy?

A

Bulbospinal neuropathy or Kennedy’s disease

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14
Q

Which inherited ataxias show anticipation?

A

Friedreich’s ataxia

Spinocerebellar ataxia

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15
Q

What are the other names of Dentatorubral pallidoluysian atrophy?

A

Haw River Syndrome OR

Naito-Oyanagi disease

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16
Q

Name four diseases with CAG triplet repeats?

A

Huntington’s disease

Spinocerebellar ataxia

Kennedy disease/spinobulbar muscular atrophy/bulbospinal neuropathy

Dentatorubral pallidoluysian atrophy

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17
Q

What are the triplet repeats of Huntington’s disease, Fragile X syndrome, Friedreich’s ataxia and Myotonic dystrophy?

A

Huntington’s disease = CAG

Fragile X syndrome = CGG

Friedreich’s ataxia = GAA

Myotonic dystrophy = CTG

18
Q

What is the inheritence pattern of Fragile X syndrome?

A

X-linked dominant (complex X-linked)

19
Q

What is the inheritence pattern of Huntington’s disease?

A

Autosomal dominant

20
Q

What is the inheritence pattern of myotonic dystrophy/Dystrophia myotonica?

A

Autosomal dominant

21
Q

What is the inheritence pattern of Friedreich’s ataxia?

A

Autosomal recessive

22
Q

Which type of myotonic dystrophy mainly has triplet expansion?

A

Myotonic dystrophy type 1

23
Q

What is the inheritence pattern of Spinocerebellar ataxia?

A

Autosomal dominant (mostly)

24
Q

What is the inheritence pattern of Kennedy syndrome (Spinobulbar muscular atrophy/bulbospinal atrophy)?

A

X-linked Recessive

25
Q

What is the inheritence pattern of Dentatorubral pallidolusyian atrophy?

A

Autosomal dominant

26
Q

Huntington’s diease: chromosome & gene

A

Chromosome 4:

gene HTT (aka IT15, or Huntingtin gene)

(HTT = Huntingtin; IT15 = Interesting type 15)

(Recall: CAGe has 4letters)

27
Q

What is the protein encoded by HTT gene?

A

Huntington protein

28
Q

What is the CAG repeats in normal person?

A

Around 11 to 34 (or 7 to 30)

29
Q

What is the CAG repeats in Huntington’s disease?

30
Q

What is the CAG repeats in ‘full-penetrant’ Huntington’s disease?

31
Q

Fragile X syndrome: Chromosome & gene

A

X chromosome

Gene: FMR1

(Recall: Fragile X has X in it)

32
Q

Friedreich’s ataxia: Chromosome & gene

A

Chromosome 9

Gene: FXN

33
Q

Myotonic dystrophy type 1: Chromosome & gene

A

Chromosome 19

Gene: DMPK

(Recall: Dystrophia myotonica has 19 letters)

34
Q

Which trinucleotide repeat disorder do NOT cause anticipation?

A

Firedreich’s Ataxia

35
Q

Why anticipation is NOT seen in Friedreich’s ataxia?

A

Because it is Autosomal Recessive >>> skips generation +

Diease is usually not seen in more than one generation

36
Q

In Friedreich’s ataxia, GAA repeats on FXN gene of chromosome 9 results in >>> ?

A

Defect in Frataxin (iron binding protein) >>> leads to impaired mitochondrial function

Degeneration of various spinal cord tracts

37
Q

In myotonic dystrophy, CTG repeats in DMPK gene on chromosome 19 results in >>> ?

A

abnormal expression of ‘myotonin protein kinase’

38
Q

Which has paternal anticipation?

A

Huntington’s disease

(If anticipation was seen in Friedreich’s ataxia >> it would be paternal; but friedreich do NOT have anticipation usually)

39
Q

Which has maternal anticipation?

A

Fragile X syndrome, Myotonic dystrophy

(Following transmission from affected mother)

40
Q

How gene mutation and triplet repeats are identified in the lab?

A

PCR (Polymerase chain reaction)

41
Q

What is threshold and expansion?

A

Threshold: in normal individual, number of repeats, + but remains below a defined threshold

Expansion: Increased number of repeats in an affected patient + above the disease-causing threshold

Genetics (28 decks)

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