Spinal Muscular Atrophy

Spinal muscular atrophy is a rare neuromuscular disorder that causes loss of motor neurons and progressive wasting of the skeletal muscles, most often becoming apparent in infancy or early childhood, though milder forms can appear later. Left untreated it is the most common genetic cause of infant death, with progressive weakness affecting the arms, legs, and eventually breathing muscles, along with poor head control, swallowing difficulty, scoliosis, and joint contractures. It is caused by mutations in the SMN1 gene on chromosome 5, which normally produces a protein motor neurons need to relay signals to muscle; the disease is usually inherited in an autosomal recessive pattern, though about 2 percent of cases arise spontaneously. Worldwide incidence is estimated between about 1 in 4,000 and 1 in 16,000 births.