Muscle Dystrophies

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Duchenne dystrophy is the most common form of muscular dystrophy in childhood 

Duchenne dystrophy is an X-linked recessive disorder, hence it is almost exclusively seen in males. It is caused by mutation in the gene coding for dystrophin, the protein that normally anchors the cell membrane of muscle fibres to the extracellular matrix. Lack of this protein renders fibres liable to tearing with repeated contraction. 

The onset of clinical features is in early childhood, affected children showing muscle weakness with a high serum creatine kinase level (caused by necrosis) and clinical calf hypertrophy (due to fatty replacement of muscle). The disease has a very poor prognosis, most affected individuals dying in their late teens. Heart muscle is also affected, leading to cardiomyopathy.

Histologically, there is muscle fibre necrosis, phagocytosis of dead fibres, and replacement of muscle by fibrous and fatty tissue. Immunostaining for dystrophin reveals that it is absent from fibres. 
Diagnosis can be assisted by performing molecular genetic analysis of the dystrophin gene.


Myotonic dystrophy is an autosomal dominant disorder

Myotonic dystrophy is the most common inherited muscle disease of adults, affecting 1 in 8000 of the population. It is characterized by muscle weakness, myotonia (inability to relax muscles), and several non-muscle features including cataracts and frontal baldness in males, cardiomyopathy, and low intelligence. Patients also show neurofibrillary tangles similar to those seen in Alzheimer's disease. in the brain with ageing. It is inherited as an autosomal dominant disorder and usually becomes apparent in adolescence with facial weakness and distal weakness in the limbs. Death is commonly due to involvement of the respiratory muscles.

The gene for myotonic dystrophy is located on chromosome 19, coding for a protein kinase. Histologically, affected muscles show abnormalities of fibre size, with fibre necrosis, abundant internal nuclei, and replacement by fibrofatty tissue.
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We give here simplified and accurate information about the disease

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Revised: 02-11-2014.