DNA testing in diagnosis of neurological disorders

Question 1

What are unstable repeat expansion?

Answer 1

expansion of a segment of DNA within a specific gene above the threshold - usually consists of repeating units of 3 or more nucleotides eg CAG, CCG

Question 2

what are unstable repeat expansion also called?

Answer 2

dynamic mutations -> size of the expansion is changing

Question 3

Anticipation

Answer 3

the increase in expansion size from generation to generation

Question 4

Huntinton disease is associated with what unstable repeat expansion, what are the effects?

Answer 4

CAG triplet repeat in the coding region of the HTT gene. Leads to toxin protein production Poly -Q HTT -> damages basal ganglia -> atrophy

Question 5

How does Freidrich ataxia occur? when does it usually occur in individuals?

Answer 5

GAA triplet repeat in an intron -> impaired transcription of a Frataxin protein> onset in adolescence (unlike other disorders - mostly late onset)

Question 6

People affected with HD have how many triplet repeats?

Answer 6

> 40 CAGs

Question 7

How many CAG repeats is considered normal? how many is normal mutable?

Answer 7

<26 repeats

27-35 = normal mutable (may pass on to offspring)

Question 8

What is the zone of reduced penetrance for HD?

Answer 8

36-39 CAG repeats -> individual may or may not develop the disease

Question 9

Is HD autosomal, X linked? recessive or dominant?

Answer 9

autosomal dominant

Question 10

are the spinocerebellar ataxias autosomal, X linked? recessive or dominant?

Answer 10

Autosomal dominant

Question 11

What triplet repeat is present in the spinocerebellar ataxias and what does it cause?

Answer 11

CAG repeats

mutated protein that affects the functioning of the appropriate ion channel

Question 12

Is Freidrich Ataxia autosomal, X linked? recessive or dominant?

Answer 12

Autosomal recessive

Question 13

How many repeats would an individual with freidrich ataxia have?

Answer 13

66-1700 repeats