MUSCULAR DYSTROPHIES

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.