Interestingly, spinal onset of ALS symptoms was quite common (71%) among ALS patients with one copy of SMN1. The authors proposed that the abnormal alleles could point to a linkage disequilibrium with the neuronal apoptosis inhibitor protein (NAIP) gene, which is located in close proximity to the SMN1–2 locus [66]. This evidence concerns the gene SMN1 and amyotrophic lateral sclerosis.