Although SMN2 copy number sometimes correlates with the SMA phenotype, this is not the case for all SMA patients [14,15], as supported by findings here that there were SMA patients in each severity classification (Types I, II and III) with three copies of SMN2, while a Type III SMA patient was identified with only two copies of SMN2. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.