Approximately 95%-98% of individuals with a clinical diagnosis of SMA lack exon 7 in both copies of SMN1 gene, while approximately 2%-5% of them are compound heterozygotes for deletion of SMN1 in one allele and an intragenic mutation of SMN1 in another allele [5,6]. The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.