A total of more than 95% of patients with SMA (this proportion is lower in African black patients with SMA) present homozygous absence of at least exon 7 of the SMN1 gene on chromosome 5q13, and the remaining patients (less than 5%) show compound heterozygous variants with an intragenic mutation on one allele and a deletion or gene conversion on the other [33–35]. Here, SMN1 is linked to proximal spinal muscular atrophy.