All SMA types are associated with the mutation of the SMN1 gene that, with its paralog SMN2 (NM_017411.4) and with the NLR family apoptosis inhibitory protein/BIRC1 (NAIP) gene (NM_004536.2), lies within a segmental duplicated region on chromosome 5q13. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.