SMN1 and proximal spinal muscular atrophy: Interestingly, it is known that the survival motor neuron 2(SMN2) gene (an almost identical copy of SMN1) is notable to fully compensate for the lack of SMN1 (and its functional geneproduct: full-length survival motor neuron (SMN) protein (SMN-FL)) in SMA patients; this isbecause, compared to SMN1, SMN2 has a translationallysilent C-to-T transition at position 6 in its seventh exon that, via alternative splicing,causes more than 90% of the SMN protein produced by cells to be truncated and thusnon-functional [9,10].