Mutated genes most recently identified that cause metabolic myopathy include PGM1, GYG1, RBCK1, VMA21, MTO1, KARS, and ISCA2. Myopathy may occur in a non-syndromic setting (isolated), but most frequently, myopathy is a collateral feature of the phenotype. The gene discussed is GYG1; the disease is metabolic myopathy.