Muscle-energy GSDs include McArdle disease (GSD V, deficiency of myophosphorylase encoded by PYGM), GSD VII (Tarui disease, deficiency of phosphofructokinase-M encoded by PFKM), IXβ (deficiency of PhK due to β subunit defect encoded by PHKB), X (deficiency of muscle phosphoglycerate mutase encoded by PGAM2), XI (deficiency of lactate dehydrogenase A encoded by LDHA), XII (deficiency of fructose-1,6-biphosphate aldolase A encoded by ALDOA), XIII (deficiency of β-enolase encoded by ENO3), and phosphoglycerate kinase deficiency (encoded by PGK1). The gene discussed is PGK1; the disease is glycogen storage disease V.