SMN2 and proximal spinal muscular atrophy: All but one SMA case within this cohort, whose genotype remains unknown, possessed two copies of SMN2. This case has the shortest postnatal survival of just 7 days and is likely to reflect either 1 or 2 copies of SMN2, as 3 copies of the SMN2 gene are associated with significantly longer survival [14, 43, 70].