SMN1 and motor neuron disorder: Spinal muscular atrophy (SMA) is a rare hereditary motor neuron disorder, with an estimated prevalence of 1 or 2 in every 100,000 persons and an incidence of approximately 1 in every 10,000 live births, caused by an insufficient level of survival motor neuron (SMN) protein due to SMN1 gene homozygous deletion or mutation [1,2].