IGFBP5 and amyotrophic lateral sclerosis: The difference in IGFBP-1 could be explained by the fact that both IGFBP-3 and IGFBP-5 are major IGF transporters and the only IGFBPs that are bound to ALS, whereas IGFBP-7 binds IGFs with considerably less affinity than IGFBP-3 or IGFBP-5 [23].