SMN2 and proximal spinal muscular atrophy: Notably, β-agonist stimulation increased the expression of survival of motor neuron 2 (smn2), suggesting that, in addition to having an indirect effect on skeletal muscle atrophy, activation of β-adrenergic signaling ameliorates spinal muscular atrophy (SMA) phenotype by directly increasing the levels of expression of smn258, 59.