Spinal muscular atrophy (SMA) is rare, occurring in approximately 1 in 10 000 newborns, 1–3 but it is associated with considerable clinical, psychosocial, and economic burden.4–9 SMA is an autosomal recessive disease characterized by progressive degeneration of the motor neurons, resulting in atrophy of skeletal muscles and generalized weakness.1–3 The most common form of SMA is caused by mutations in the SMN1 gene on chromosome 5q, which result in a relative deficiency of SMN protein. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.