McArdle's disease: a nonsense mutation in exon 1 of the muscle glycogen phosphorylase gene explains some but not all cases.

McArdle's disease is an inherited disease that results from a lack of functional muscle glycogen phosphorylase. We report here the identification of a C to T transition in exon 1 of the muscle phosphorylase gene found in all patients studied. This base pair mutation results in the substitution of a stop codon (TGA) for the codon (CGA) for Arg49 in the mature protein, and generates a novel restriction site for NlaIII. Of sixteen McArdle's patients, ten are homozygous for this mutation; the remainder are heterozygous. Additional unidentified mutations must lead to the McArdle's phenotype in the latter group of patients.