Most commonly, 96% of SMA patients carry a homozygous deletion of SMN1 exon 7 and 8 or exon 7 only (Kolb and Kissel, 2015; Verhaart et al., 2017a; Wirth, 2000); the remaining 4% are compound heterozygotes (Mercuri et al., 2018; Wirth et al., 1999). The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.