SMN2 and proximal spinal muscular atrophy: Severe-SMA mice harbouring two SMN2 copies, or with an extra SMNΔ7 cDNA transgene (SMA Δ7 mouse model), develop early and rapidly progressive pathology, dying within 1–2 weeks postnatally (Hsieh-Li et al, 2000; Le et al, 2005; Monani et al, 2000; Riessland et al, 2010).