To investigate a potential correlation between impaired snRNP assembly and SMA severity, we analyzed SMN complex expression and snRNP assembly activity in the spinal cord of different mouse models of SMA, including SMNΔ7 SMA mice, mild SMN(A2G) SMA mice and phenotypically rescued high copy SMN2 SMA mice. This evidence concerns the gene LSM2 and proximal spinal muscular atrophy.