Genomic variability in the survival motor neuron genes (SMN1 and SMN2): Implications for spinal muscular atrophy phenotype and therapeutics development Genomic variability in the survival motor neuron genes (SMN1 and SMN2): Implications for spinal muscular atrophy phenotype and therapeutics development Int J Mol Sci Int J Mol Sci 2021 2021 22 22 7896 7896 7896 7896 10.3390/ijms22157896 10.3390/ijms22157896 34360669 34360669. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.