
MUSCULAR DYSTROPHIES
This is a group of inherited disorders characterized by progressive degeneration of groups of muscles,sometimes with involvement of the heart muscle or conducting tissue and other parts of the nervous system.
MYOTONIC DYSTROPHY
Autosomal dominant; expanded triplet repeat chromosome 19q,
Age of onset-occurs at any age
Muscles affected –face(including ptosis),sternomastoids,distal limb,and generalized later.
Other features-myotonia,cognitive dulling,cardiac conduction abnormalities,lens opacities ,frontal balding and hypoganadism.
PROXIMAL MYOTONIC MYOPATHY(PROMM;DM2)
Autosomal dominant;quadruplet repeat expansion in zn finger protein 9 gene chromosome 3q
Age of onset-adult
Muscles affected-proximal,especially thigh ,sometimes muscle hypertrophy.
Other features-As for DM 1 but cognition not affected,muscle pain.
DUCHENNE
X-linked;deletion in dystorphin gene
Age of onset-first 5 years
Muscles affected-proximal and limb girdle
Other features- pseudohypertrophy of clves,cardiomyopathy.
BECKER
X-linked ;deletions in dystrophin gene
Age of onset-late childhood/early adult
Muscles affected-proximal and limb girdle
Other features –pseudohypertrophy of calves,cardiomyopathy
LIMB GIRDLE
Autosomal dominant (type-1),autosomal recessive (type-2),many mutations on different chromosomes
Age of onset-childhood/early adult
Muscles affected-limb girdle
Other features-some have calf hypertrophy ,some have cardiac conduction abnormalities.
FACIOSCAPULOHUMERAL(FSH)
Autosomal dominant; tandem repeat deletion chromosome 4q
Age of onset-7-30 years
Muscles affected –face and upper limb ,girdle.
Other features –pain in shoulder girdle common.
OCULOPHARYNGEAL
Autosomal dominant and recessive;triplet repeat expansion in PABP2 gene chromosome 14q
Age of onset-30-50 years
Muscles affected-ptosis,external opthalmoplegia, dysphagia,tongue weakness
Others features-mild lower limb weakness
EMERY-DREIFUSS
X-linked recessive;mutation in emerin gene
Age of onset-4-5 years
Muscles affected-humero-peroneal,proximal limb girdle later
Others features-contractures develop early ,cardiac involvement leads to sudden death
Clinical features
Onset is often in childhood ,although some patients especially those with myotonic dystrophy, may present as adults.
Wasting and weakness are usually symmetrical,there is no fasciculation and no sensory loss,except in myotonic dystrophy.
Differential diagnosis is based on the age at onset ,the distribution of affected muscles and the pattern of inheritance
Myotonic dystrophy may be diagnosed clinically by the distribution of muscle weakness and other features including myotonia, many dystrophies include cardiomyopathy amongst their clinical features.