Manifesting heterozygotes in a Japanese family with a novel mutation in the muscle-specific phosphoglycerate mutase (PGAM-M) gene.

Muscle-specific phosphoglycerate mutase (PGAM-M) deficiency results in a metabolic myopathy (glycogenosis type X). Three mutations in the PGAM-M gene have been described thus far, two in African-American families and one in a Caucasian family. In two of them, manifesting heterozygotes were documented. We found a new PGAM-M mutation in a Japanese family with partial PGAM deficiency: a G-to-A transition at nucleotide position 209, resulting in the substitution of a highly conserved glycine at codon 97 with aspartic acid (G97D). Two heterozygous family members for the G97D mutation presented with exercise intolerance and muscle cramps. We describe the first PGAM-M mutation in the Japanese population and confirm that heterozygous individuals can be symptomatic.