Dystrophin is absent -
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 Becker's 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.
Duchenne muscular dystrophy
Becker's muscular dystrophy
Myotonic dystrophy
Limb-Girdle dystrophy
Mendelian Disorders: Single-Gene Defects