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Clinical Cytogenetics and Molecular Genetics > Trinucleotide Repeats > Flashcards

Trinucleotide Repeats Flashcards

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1
Q

__________ is when the gene is passed on from generation to generation the number of tandem repeats can increase (expands) leading to worsening abnormalities in gene expression and function: Earlier onset, worse phenotype

A

anticipation

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2
Q

Tandem repeat gene disorders with maternal expansion

A

Myotonic dystrophy and Fragile X

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3
Q

Tandem repeat gene disorder with paternal expansion

A

Huntington’s disease

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4
Q

Mechanism of Fragile X and Friedereich Ataxia

A

Failure to transcribe/translate gene product

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5
Q

Mechanism of Huntingtons, DRPLA, SCA and SBMA

A

Build up of aggregates

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6
Q

Mechanism of myotonic dystrophy and fragile X tremor/ataxia syndrome (FXTAS)

A

Interference with neighboring genes (in transcription)

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7
Q

First tandem repeat disorder discovered

A

Fragile X syndrome 1991

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8
Q

1 cause of ataxia in adults

A

Friedreich ataxia

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9
Q

1 cause of inherited moderate intellectual disability?

A

Fragile X
second only to trisomy 21

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10
Q

Fragile X gene?

A

FMR1 - fragile X messenger ribonucleoprotein
FMR2

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11
Q

Fragile X is caused by a _______________ repeat in the _____________ region of the ______________ gene and chromosome _______________

A

CGG
5 prime UTR
FMR1
Xq27F

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12
Q

Friedreich ataxia is caused by a ________ trinucleotide repeat in the ___________ gene on chromosome ______________ and in the _____________ (exon/intron)

A

GAA
X25
9q13
intron

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13
Q

Fragile X is observed after _____________ CGG repeats

A

> 230 CGG

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14
Q

Friedreich ataxia is observed after ___________ GAA repeats

A

> 100 GAA

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15
Q

Myotonic dystrophy is caused by a ____________ repeat in the _____________ gene on chromosome _____________ in the ___________ region

A

CTG
DMPK
19q13
3 prime UTR

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16
Q

Myotonic dystrophy is observed after ___________ CTG repeats

A

50-thousands

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17
Q

Huntington disease is caused by a ______________ repeat in the ____________ gene on chromosome __________________ in the ______________ (exon/intron)

A

CAG
HDD
4p16
exon

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18
Q

Spinobulbar atrophy (Kennedy disease) is caused by a ________________repeat in the _____________gene on chromosome _____________________ in the ___________________ (exon/intron)

A

CAG
AR
Chromosome Xq13
exon

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18
Q

Hungtington disease is observed after __________________ CAG repeats

A

36-121

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19
Q

Spinobulbar atrophy is observed after __________________ CAG repeats

A

38-62

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20
Q

Loss of frataxin leads to altered _____________ homeostasis and ____________ dysfunction

A

iron
mitochondrial

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21
Q

Most tandem repeat disorders have ______________ __________________ inheritance

A

autosomal dominant

22
Q

SBMA (Kennedy syndrome) has _______ _____________ inheritance

A

X-linked

23
Q

Friedreich ataxia has _____________ _______________ inheritance

A

AR

24
Q

The most common mechanism underlying all tandem repeat disorders

A

slipped pairing

25
Q

FXTAS fragile x tremor ataxia syndrome is caused by ____________ to __________________ repeats of CGG

A

65-200

26
Q

Tandem repeats with long face, bossed forehead, ID, autism, large ears, flexible joints, macroorchidism, single palmar crease and flat feet

A

Fragile X syndrome

27
Q

Fragile X syndrome is due to __________________ of FMR1 while FXTAS is due to _____________________

A

Fragile X due to loss of expression of FMR1 - loss of dendritic pruning and altered signaling
FXTAS - overproduction of FMR1 mRNA (reduced protein)

28
Q

FXTAS occurs in the ________________ of children with Fragile X and shows increased (2-5x) FMR1 mRNA production, decreased FMR1 protein production and cytoplasmic inclusions which label with _____________

A

grandfathers
ubiquitin

29
Q

FMR1 expands in _______________ alleles

A

maternal

30
Q

In the 5 prime UTR of FMR1 on chromosome Xq27.3 the CGG repeats can be interrupted by ________ repeats at 9/10 or 19/20 which decreases CGG expansion

A

AGG
Sequence of 33-39 CGG repeats after the AGG (uninterrupted) leads to instability of maternal

31
Q

How is Friedreich ataxia (FRDA) inherited and does it show anticipation?

A

AR - chromosome 9q13
No anticipation

32
Q

In addition to ataxia, FRDA causes lack of iron integration into ______________ and _____________ of spinal neurons as well as loss of PVT, diabetes and cardiomyopathy

A

mitochondria
ferroptosis

33
Q

The FRDA ___________ expansion occurs where in the gene?

A

GAA (german ataxia ataxia)
intron (Alu/SINE element)

34
Q

96% of FRDA have ______________ expansion alleles

A

homozygous

35
Q

Myotonic dystrophy is due to ____________ repeats in 3prime UTR of DMPK (DM1) and __________ repeats in DM2 (ZNF9)

A

CTG
CCTG

36
Q

DM anticipation is through the __________________ (maternal/paternal)

A

maternal

36
Q

DM is a multisystem disorder, involving smooth and cardiac muscle wasting, the CNS and endocrine glands (pancreas=diabetes), and it causes __________ in the eyes, hypersomnia, premature balding and calcifying epithelioma (pilomatrixoma)

A

cataracts

37
Q

Myotonic dystrophy is associated with ______________ repeats of CTG

A

50-thousands

37
Q

FMR1 testing no 1 and no 2

A
  1. microarray and FMR1
  2. panel testing
38
Q

In myotonic dystrophy (DM) variant _____________ sequences interrupt the CTG repeat and stabilize anticipation

A

repeat
CCG, CGT, CGG, CAG

38
Q

DMPK shows somatic ______________ and multiple possible mechanisms including RNA toxicity, altering expression neighboring genes and haploinsufficiency

A

mosaicism

39
Q

Myotonic dystrophy testing includes: _______________–

A

physical exam and history
TP-PCR
panels - but mosaic

40
Q

Polyglutamine (CAG tandem repeat disorders) show __________ ____________ inheritance and ______________ anticipation with a gain of function in huntingtin

A

autosomal dominant
paternal anticipation

41
Q

Polyglutamine protein aggregates found in the _______________________

A

nucleus

42
Q

HDD is penetrant at greater than ____________ CAG repeats

A

36

43
Q

CAG repeats occur in the _____________ exon of HDD

A

First

44
Q

Two X-linked tandem repeat disorders

A

Fragile X
SBMA

45
Q

In SBMA the CAG repeat occurs in the first ___________ (exon/intron) of the _________ gene

A

exon
AR

46
Q

Tandem repeat disorder that affects the anterior horn, dorsal horn and bulbar region and may cause androgen insensitivity and gynecomastia

A

SBMA
Kennedy syndrome

47
Q

Spinocerebellar ataxias are caused by __________ tandem repeats in genes such as SCA1, 2, 3 ….

A

CAG

48
Q

Inheritance pattern of ALS?

A

Autosomal dominant

49
Q

ALS is caused by a _____________ tandem repeat in the _____________ gene

A

hexanucleotide (GGGGCC)
C9orf72 gene

50
Q

ALS phenotype (UMN, LMN and dementia) at ______________ repeats

A

> 60

Clinical Cytogenetics and Molecular Genetics (20 decks)

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