Source : WordNet®

Becker muscular dystrophy
     n : a form of muscular dystrophy that set in in adolescence or
         adulthood and progresses slowly but will affect all
         voluntary muscles; characterized by generalized weakness
         and muscle wasting that affects limb and trunk muscles
         first; similar to Duchenne's muscular dystrophy but less
         severe; inheritance is X-linked recessive (carried by
         females but affecting only males)