Myotonic dystrophy

Question 1

_____ is an autosomal dominantly inherited condition w/ a frequency of around ____ and is the most common inherited neuromuscular condition.

Answer 1

Myotonic dystrophy (dystrophia myotonica or DM); 1 in 7500

Question 2

Myotonic dystrophy involves progressive ____, _____, and ____, in addition to a tendency to cardiac conduction defects & risks associated w/ general anaesthesia.

Answer 2

muscle weakness; myotonia; cataracts

Question 3

The genetic basis of myotonic dystrophy is an unstable length mutation of a ____ repeat tract within the 3 ′ UTR of the ____ gene.

Answer 3

CTG; DMPK

Question 4

It is believed that the resulting abnormal DMPK mRNA indirectly exerts a toxic intracellular effect on the splicing of other genes such as the _____, w/c appears to be responsible for the myotonia.

Answer 4

chloride channel 1 ( CLCN1 ) gene

Question 5

T/F. The expression levels of genes adjacent to DMPK also appear to be increased by the presence of the expanded repeat tract.

Answer 5

False. Reduced

Question 6

Normal individuals show stable minor length variations with _____ repeats whereas, in DM, large expansions, usually _____, are seen and these larger repeat tracts are unstable.

Answer 6

4 – 37 CTG; over 100 repeats but may be over 2000

Question 7

T/F. For the offspring of an affected male, half will be affected & half will be unaffected. In contrast to affected females, however, the risk of a neonatal affected case is minimal.

Answer 7

True.

Question 7

T/F. There is a general (but incomplete) correlation between the size of the repeat sequence & the clinical severity, w/ congenitally affected infants usually possessing more than 1000 CTG repeats.

Answer 7

True.

Question 8

Presymptomatic carrier detection and prenatal diagnosis are possible by ____.

Answer 8

DNA analysis.