This caution is of importance since only a genetic alteration within exon 7 has been proven to cause SMA.28 Previous studies have shown variable severity among individuals with more than one SMN2 copies and non-deletion of NAIP. It is therefore not recommended to determine the severity if the fetus has a genotypic pattern other than those described within Figure 1. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.