DNA Testing Flashcards
What kind of inherited genetic disorder can lead to neurological disorder with loss of movement control?
unstable repeat expansions
T/F Expansions typically occur in a single chromosome in adjacent fashion
True
T/F tetranuleotide repeat is the most common form of unstable repeat expansion
False, tri-nucleotide repeat is
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
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
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.
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
How do repeats in coding region cause disorders?
change in codon sequence can give new property to encoded protein, and the protein becomes toxic
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
T/F Friedriech ataxia generally has an earlier onset than other disorders
True, usually earlier than HD and SCA
T/F Huntington’s disease is an autosomal dominant disorder
True
What are the main features of HD
movement disorder
cognitive disorder
emotional disorder
T/F HD is caused by repeats of CCG in chromosome 4
False, it’s caused by CAG in chromosome 4
T/F If you have more than 40 repeats in the gene huntingtin, you will definitely develop HD
True, >40 = fully penetrant
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
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
What is the main test for diagnosing HD?
fluorescent nucleotide testing
Is predictive tests usually done for HD?
No, because there is no cure even if the condition is diagnosed
T/F Spinocerebellar ataxia conditions are all caused by unstable repeats
False, only 10 types are caused by unstable repeats
T/F Friedreich ataxia is an autosomal recessive disorder
True
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
What are the main features of FA?
progressive limb and gait ataxia
cardiomyopathy
diabetes
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
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
