Neuronal apoptosis inhibitor protein (NAIP) was the first human inhibitor of apoptosis protein (IAP) identified and was discovered by its association with the neurodegenerative disorder spinal muscular atrophy. Members of the IAP family contain one to three copies of an approximately 70 amino acid motif termed baculovirus IAP repeat (BIR); these BIRs promote protein-protein interactions with various caspases such as caspase-3, -7, and -9 as well as members of the TRAF family of signal molecules (reviewed in 3). Unlike other IAPs however, NAIP requires ATP to bind caspase-9 and is not inhibited by the IAP-inhibiting molecule Smac/DIABLO, suggesting that NAIP is unique among the IAPs in its regulation of its activity. Finally, although only one human NAIP protein has been identified, other shorter NAIP mRNA transcripts have been reported.