SMN1 and proximal spinal muscular atrophy: Finally, the gene for neuronal apoptosis inhibitory protein (or NLR family apoptosis inhibitor protein; NAIP) is located within the genomic region of chromosome 5 that encompasses SMN1. NAIP is not the causative gene for SMA but NAIP mutations are suggested to modify disease severity in patients with SMA [78, 79], albeit their clinical significance is unclear [4].