SMN2 and proximal spinal muscular atrophy: The constructs were then packaged into AAV9 and injected intravenously into SMNΔ7 mice, which is a severe SMA mouse model that harbors a single targeted null mutation (SMN–/–) and two transgenic alleles (hSMN2+/+and SMNΔ7+/+), recapitulating many of the clinical features observed in SMA type 1, such as motor neuron loss, motor function deficits, and early death.