<prompt> Dystrophin is absent -Duchenne muscular dystrophyBeckers muscular dystrophyMyotonic dystrophyLimb-Girdle dystrophy  <response>: Ans. is a i.e., Duchenne muscular dystrophy o DMD, also calledpeudohypertrophic mucular dystrophy, is the most common hereditary neuromuscular dystrophy. It is an X-linked recessive disorder. It is caused by a mutation in gene responsible for producing dystrophin a sarcolemmal protein.o The usual age of onset is 3-5 years does not present at birth or infancy, i.e., disease begin to manifest when child starts walking.o There is progressive muscle weakness affecting proximal muscles of limbs. Child walks clumsily, has difficulty in climbing stairs and the gait is waddling Trendelenburg. Because of weakness of proximal thigh muscles, there is compensatory hypertrophy of distal calf muscles. This is called pseudohypertrophy because it is not true hypertrophy of muscles, instead the muscle is replaced by fat and connective tissue. Extraocular muscles are spared.o Other features are scoliosis, epilepsy and mild mental retardation. Patient die in the second decade of life because of respiratory failure and cardiomy opathy. Gower sign is positive, i.e. the child uses hand support to stand from sitting position because of proximal weakenss.o Serum creatinine phosphokinase CPK levels are elevated many folds. Histopathology demonstrates diffuse degeneration and muscle fibres of varying size.o Beckers muscular dystrophy is a milder version of Duchenne muscular dystrophy in which dystrophin is not completely absent. It is also X-linked recessive disorder and has less severity than DMD. 