SMN1 and proximal spinal muscular atrophy: Here, in SMA, the SMN protein with an A111G mutation (SMNA111G) is capable of snRNP assembly, and can rescue SMA mice that lack Smn and contain either one or two copies of SMN2. This correction of SMA was directly linked to the correction of snRNA levels and snRNP assembly activity in the spinal cord, which supports snRNP assembly as the critical function affected in SMA and suggests that the levels of snRNPs are critical to motor neurons [17].