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Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease characterized by loss of anterior horn cells in the spinal cord and concomitant symmetrical muscle weakness and atrophy (PMID: 16364894 ). SMA is caused by deletion or mutations of the survival motor neuron (SMN1) gene. SMA patients lack a functional SMN1 gene, but they possess an intact SMN2 gene, which though nearly identical to SMN1, is only partially functional (PMID: 17355180). A large majority of SMN2 transcripts lack exon 7, resulting in production of a truncated, less stable SMN protein (PMID: 10369862). The level of SMN protein correlates with phenotypic severity of SMA.