Large deletions involving genes from the same locus where SMN1 is located, for example, NAIP and SERF1A (encoding NLR family apoptosis inhibitory protein, and Small EDRK-rich factor 1, respectively) [33,34,86] are observed in patients with severe forms of SMA, but not in mild forms. The gene discussed is NAIP; the disease is proximal spinal muscular atrophy.