Muscular dystrophies Flashcards
What is Becker muscular dystrophy?
Becker muscular dystrophy is an x-linked recessive dystrophinopathy, often thought of as a ‘less severe’ version of Duchenne muscular dystrophy.
What causes Becker muscular dystrophy?
It is caused by a mutation in the gene encoding dystrophin, located on Xp21.
What is the role of dystrophin in muscles?
Dystrophin is part of a large membrane-associated protein that connects the muscle membrane to actin, which is part of the muscle cytoskeleton.
How does the mutation in Becker muscular dystrophy differ from Duchenne muscular dystrophy?
In Duchenne muscular dystrophy, there is a frameshift mutation that results in the loss of one or both binding sites, leading to a severe form. In Becker muscular dystrophy, there is a non-frameshift insertion that preserves both binding sites, resulting in a milder form.
At what age does Becker muscular dystrophy typically develop?
Becker muscular dystrophy develops after the age of 10 years.
Is intellectual impairment common in Becker muscular dystrophy?
Intellectual impairment is much less common in Becker muscular dystrophy than in Duchenne muscular dystrophy.
What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy is an X-linked recessive inherited disorder in the dystrophin genes required for normal muscular function.
What are the features of Duchenne muscular dystrophy?
Features include progressive proximal muscle weakness from 5 years, calf pseudohypertrophy, Gower’s sign, and 30% of patients have intellectual impairment.
What is Gower’s sign?
Gower’s sign is when a child uses arms to stand up from a squatted position.
What investigations are used for Duchenne muscular dystrophy?
Investigations include raised creatinine kinase and genetic testing, which has now replaced muscle biopsy for a definitive diagnosis.
What is the management approach for Duchenne muscular dystrophy?
Management is largely supportive as there is currently no effective treatment.
What is the prognosis for children with Duchenne muscular dystrophy?
Most children cannot walk by the age of 12 years, and patients typically survive to around the age of 25-30 years.
What cardiac condition is associated with Duchenne muscular dystrophy?
Duchenne muscular dystrophy is associated with dilated cardiomyopathy.
What is myotonic dystrophy?
Myotonic dystrophy (also called dystrophia myotonica) is an inherited myopathy that typically develops around 20-30 years old, affecting skeletal, cardiac, and smooth muscle.
What are the two main types of myotonic dystrophy?
The two main types of myotonic dystrophy are DM1 and DM2.
What is the genetic cause of DM1?
DM1 is caused by a CTG repeat at the end of the DMPK (Dystrophia Myotonica-Protein Kinase) gene on chromosome 19.
What is the genetic cause of DM2?
DM2 is caused by a repeat expansion of the ZNF9 gene on chromosome 3.
What are the key differences between DM1 and DM2?
DM1 is associated with distal weakness and involves the DMPK gene on chromosome 19, while DM2 is associated with proximal weakness and involves the ZNF9 gene on chromosome 3. Severe congenital form is not seen in DM2.
What are general features of myotonic dystrophy?
General features include myotonic facies (long, ‘haggard’ appearance), frontal balding, bilateral ptosis, cataracts, and dysarthria.
What are other features of myotonic dystrophy?
Other features include myotonia (tonic spasm of muscle), weakness of arms and legs (distal initially), mild mental impairment, diabetes mellitus, testicular atrophy, cardiac involvement (heart block, cardiomyopathy), and dysphagia.
DM1 vs DM2 - chromosomes, distal or proximal weakness?
