SMN1 and proximal spinal muscular atrophy: We confirmed this by comparing the amount of full-length SMN protein in isolated FAPs from the hindlimbs of control, Smn1ΔMPC mutants, and a severe SMA mouse model (Smn1−/−; SMN2+/+; SMNΔ7+/+; SMAΔ7 mutants) (Figure 2I).