SMN2 and proximal spinal muscular atrophy: Since the SM25 construct was prepared to specifically improve SMN2 exon 7 definition, we crossed the SM25 transgenic line with a severe SMA mouse model, FVB.Cg-Tg(SMN2)89Ahmb Smn1tm1Msd/J that show symptoms and neuropathology similar to SMA type I patients and survive 4–6 days.