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Flashcards in DNA Testing Deck (24):
1

What kind of inherited genetic disorder can lead to neurological disorder with loss of movement control?

unstable repeat expansions

2

T/F Expansions typically occur in a single chromosome in adjacent fashion

True

3

T/F tetranuleotide repeat is the most common form of unstable repeat expansion

False, tri-nucleotide repeat is

4

T/F The presence of these repeat genes indicates that the disease will definitely be present

False, you can have naturally occurring repeats

it's only when repeats exceed the threshold that the disease will develop

5

What is dynamic mutation?

Means that in repeat expansions, the number of repeat can increase or decrease. The number of repeats is also not identical in every cell

6

T/F the inheritance pattern can be quite variable

True, there is a range of fully penetrance type, and a range for incomplete penetrance etc.

7

How do repeats in non-coding region cause disorders?

non-coding repeats can cause loss of protein function, or create a novel property to mRNA

Fragile X syndrome is an example for both

8

How do repeats in coding region cause disorders?

change in codon sequence can give new property to encoded protein, and the protein becomes toxic

9

What's the challenge in diagnosing neurodegenerative disorders caused by repeat expansions?

the clinical presentation is very variable. Different diseases often present with similar clinical signs

10

T/F Friedriech ataxia generally has an earlier onset than other disorders

True, usually earlier than HD and SCA

11

T/F Huntington's disease is an autosomal dominant disorder

True

12

What are the main features of HD

movement disorder
cognitive disorder
emotional disorder

13

T/F HD is caused by repeats of CCG in chromosome 4

False, it's caused by CAG in chromosome 4

14

T/F If you have more than 40 repeats in the gene huntingtin, you will definitely develop HD

True, >40 = fully penetrant

15

What happens if an individual has 27-35 repeats in huntingtin?

The patient will not develop HD, but there may be expansion in sperm/egg, and offsprings are at risk of developing HD

16

T/F PCR is accurate in diagnosing HD

False, it's not accurate because DNA slipping (the mechanism of repeat expansion) occurs when doing PCR

17

What is the main test for diagnosing HD?

fluorescent nucleotide testing

18

Is predictive tests usually done for HD?

No, because there is no cure even if the condition is diagnosed

19

T/F Spinocerebellar ataxia conditions are all caused by unstable repeats

False, only 10 types are caused by unstable repeats

20

T/F Friedreich ataxia is an autosomal recessive disorder

True

21

What is the proposed pathogenesis in FA?

there are repeats in introns which cause some secondary structural changes in DNA, so protein transcription is inhibited

22

What are the main features of FA?

progressive limb and gait ataxia
cardiomyopathy
diabetes

23

T/F The test for FA is simpler than that of HD

True, because there is usually massive repeat expansion in FA, so a simple gel electrophoresis can detect the genetic disorder

24

How is FA treated nowadays

We can improve the movement disorder by surgically removing the contracture, but there is no therapy for cardiomyopathy and diabetes