SMN2 and proximal spinal muscular atrophy: In general, Type 0 SMA have one copy of SMN2, Type I SMA patients have two copies of SMN2, Type II SMA patients have three copies of SMN2, Type III SMA patients have three or four copies of SMN2, and Type IV SMA patients have four or greater copies of SMN2 (Feldkotter et al., 2002; Wadman et al., 2020).