Spinal muscular atrophy (SMA) is characterized by progressive muscle weakness. Onset ranges from before birth to adolescence or young adulthood. Poor weight gain, sleep difficulties, pneumonia, scoliosis, and joint contractures are common complications. Approximately 96% of patients with SMA show homozygous absence (deletion or gene conversion) of SMN1 exon 7. The remaining patients have compound heterozygosity with a single SMN1 exon 7 deletion/gene conversion and point mutation on the other allele. This test does not detect point mutations nor does it detect SMN2 copy number.