From a total of 785 parents with at least one SMA-affected child, who were considered to be obligate carriers of SMA, 96.69% (n = 759) had one copy, 3.06% (n = 24) had two copies and 0.25% (n = 2) had three copies of SMN1. Table 3 presents the proportion of SMA parents with two copy numbers of SMN1 from various countries. The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.