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Muscle Dystrophies |
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DUCHENNE DYSTROPHY
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
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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