SMN1 and proximal spinal muscular atrophy: A commonly used mouse model of spinal muscular atrophy is the SMNΔ7 model in which the endogenous murine gene Smn1 is inactivated and replaced by two human genes, SMN2 and SMN2Δ7 (mSmn-/-; hSMN2+/+, hSMN2Δ7+/+).