SMN1 is located on chromosome 5q13 and is one of two genes encoding the SMN protein.1,2 The incidence of SMA in Europe is about 1/10,000 livebirths with a carrier frequency of 1/50.3 Based on the onset of clinical symptoms, the achievement of motor milestones, and life expectancy, SMA is divided into four subtypes (SMA type 0–4) according to the International SMA Consortium. The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.