Myotonic dystrophy Flashcards
Prevalence?
1/8000
Symptoms of myotonic dystrophy?
Muscle weakness and wasting, myotonia, cataracts, cardiac conduction abnormalities
Males- frontal balding and gynaecomastia
(some symptoms show incomplete penetrance)
Age of onset?
Between 20 and 50
Mode of inheritance?
Autosomal dominant, shows anticipation
Where are most cases referred from, and for what reasons?
Tiredness, fatigue, hands locking up, choking on food, palpitations, general anesthetic reactions
Cause of DM?
CTG repeat in the 3 ‘UTR of the DMPK gene chr 19
Allele classification:
a) normal
b) intermediate
c) affected
d) congenital
a) 5-36
b) 37-50
c) >50
d) >1000
What are the risks of intermediate range?
Repeat is unstable at this length; if repeat is transmitted to offspring there is a chance number of repeats will increase
Manifestation of repeat lengths in “affected” range
a) 50-100
b) 100-1000
c) >1000
a) mild and later onset
b) classic phenotype
c) congenital onset
How does congenital DM present a) early life b) at birth
a) extra fluid around baby, decreased foetal movements, club foot
b) hypotonia, developmental delay, progressive myopathy
Under what circumstances is congenital DM seen?
Only when the condition is transmitted by the mother
Main differential diagnosis for DM?
DM2- rare, mostly proximal weakness, mild myotnia and muscle pain. Caused by CCTG expasion, milder than DM1
Interventions for DM?
Physical DM, advice about anaesthetics, cataracts and heart screening
What can be done pre-natallly for DM?
PND and PGD
Testing for DM?
Fluorescent PCR (with at least two sizing controls), can detect alleles up to 80 repeats
TP-PCR- unable to size expanded repeat but can detect large alleles
Combination of tests sufficient for nearly all patients; tests run in parallel
