Duchenne Muscular Dystrophy (DMD)
Most common muscular dystrophy; x-linked recessive disorder – mutation of chromosome X at location p21 (dystrophin gene) reduced or impaired dystrophin (stabilises cell membrane within muscle cell); affecting boys – usually starts before 5 years (mean age of presentation is 3.5yrs); affects about 1/3500 male births;
Clinical features:
Pelvic girdle affected first with proximal muscles initially showing signs of weakness clumsy waddling wide based gait. Shoulder girdle affected next. Delayed motor milestones – tend to walk and run at later age than peers (early motor development often normal or slight delay). May have trouble climbing stairs or getting up from the floor (Gower’s sign). Frequent falls. Protuberant abdomen from lumbar lordosis. Progressive distal limbs become affected. Calf muscles enlarged from fat cells replacing muscle.
Usually in wheelchair by 10-12 years and usually die of cardiovascular complications before age 30.
Calf muscle contracture equinus and toe walking a common early sign
Laboratory findings – creatine kinase elevated up to 20x
Management:
No cure; adaptive equipment; prednisone can delay onset of loss of ambulation by up to 2 years; surgical management of scoliosis
Lower limb – stretching and night splints for equinus; surgical release of contracture may keep ability to walk
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