SMN2 and spinal muscular atrophy, type 1: To note, the additional higher molecular weight SMN band, most clearly observed in the carrier and SMA Type 1 patient samples, is most likely a recently identified splice variant of both SMN1 and SMN2 that excludes exon 7 (54 nts) but includes an exon designated 6B (109 nts), termed SMN6BΔ7 [24].