SMN2 and amyotrophic lateral sclerosis: However, Smn also associates with several other proteins which are not part of the SMN complex like HuD or hnRNP R [18], [19], [25], [29], the fragile X mental retardation protein (FMRP) [30], the ALS-related proteins FUS and TDP43 [31]–[34], and several other members of the heterogeneous nuclear ribonucleoprotein family [35].