Two proteins were higher in PBMCs from ME/CFS patients than controls; HK2 (hexokinase2), which catalyses the rate-limiting and first obligatory step of glycolysis, and PCK2 (phosphoenolpyruvate carboxykinase 2), a mitochondrial enzyme that catalyses the conversion of oxaloacetate to phosphoenolpyruvate as a rate-limiting step in gluconeogenesis. Here, PCK2 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.