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.