In accordance with the linkage data, there were no nonsynonymous mutations in SEPN1, RYR1, ACTA1, or TPM3. Moreover, none of the more than 70 other genes previously implicated in muscular dystrophies, myopathies, or spinal muscular atrophies [1] contained a homozygous or more than one heterozygous nonsynonymous mutation, once variants in dbSNP v131, 1,000 Genomes, or 56 internal genomes were discarded. The gene discussed is ACTA1; the disease is proximal spinal muscular atrophy.