Duchenne's and Becker's muscular dystrophies are associated with different levels of dystrophin. The clinical severity of the syndrome tends to be worse for lower levels of dystrophin.


Dystrophin is a 427,000 Dalton protein that is bound to actin at one end and to syntrophin at the sarcolemmal membrane at the other.


Features in common:

(1) Both affect boys, either with X-linked inheritance or as spontaneous mutation.

(2) There is progressive proximal weakness, with legs weaker than the arms.

(3) The patient shows pseudohypertrophy of the calves.

(4) There is weakness of the neck flexor muscles.

(5) There is a marked elevation in the serum CK concentration.

(6) The EMG shows myopathic changes with fibrillation potentials.

(6) The patient may develop a cardiomyopathy.

(7) The patient may develop respiratory failure.


Duchenne's MD

Becker's MD

dystrophin as percent of normal

< 3%

>= 3%


unable to walk or severely impaired

can walk as child but loses the ability as adolescent or young adult

head lag on being pulled up from the supine position


usually absent


early 20's

early 40's


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