**1.1 Overview and incidence**

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by degeneration of alpha motor neurons resulting in hypotonia, progressive muscular weakness and atrophy.30 Spinal muscular atrophy is one of the leading hereditary causes of infant mortality,31 it comprises the second most common fatal progressive diseases after cystic fibrosis.28 Spinal muscular atrophy is the most common neuromuscular disease in childhood after Duchenne muscular dystrophy with an estimated incidence of 1 per 5,000 to 10,000 live births.4,11
