Molecular characterization of McArdle's disease in two large Finnish families.

We have studied two large unrelated Finnish families with myophosphorylase deficiency (McArdle's disease). In one, we identified a new nonsense mutation at codon 540 in exon 14 of the myophosphorylase gene, changing an encoded glutamic acid to a stop codon (E540X). The second family carried a splice-junction mutation at the 5' splice site of intron 14 (1844+G-->A), previously reported in one Caucasian patient and in a consanguineous Druze family. These data further enlarge the list of mutations associated with McArdle's disease and establish that McArdle's disease is genetically heterogeneous also within the Finnish population.