High-resolution melting facilitates mutation screening of PYGM in patients with McArdle disease.

Mutations in PYGM, encoding the muscle-specific glycogen phosphorylase (myophosphorylase), are responsible for McArdle disease. Among Caucasians, a large proportion of patients are homozygous for the R50X mutation, but other mutations can affect all the 20 exons of PYGM, making mutation detection laborious. We have developed a high-resolution melting (HRM) assay for mutation detection in PYGM. Twelve McArdle patients were investigated, in whom pre-screening had ruled out homozygosity or compound heterozygosity for the two common G205S and R50X mutations. In total, we identified 16 different variations. Thirteen of these are pathogenic, and three were classified as polymorphisms. Nine variations had not previously been described. One of the novel mutations, c.2430C > T, was initially predicted to result in a silent G810G change, but cDNA analysis demonstrated that the mutation led to abnormal mRNA processing. The HRM protocol reduced the need for direct sequencing by approximately 85%, and is a good approach to search for new mutations in PYGM.