G6PD and myalgic encephalomeyelitis/chronic fatigue syndrome: Importantly, glucose-6-phosphate 1-dehydrogenase (G6PD), the enzyme catalysing the first and rate-limiting step of the oxidative arm of the PPP [42], was significantly elevated on its own by 43 ± 10% in the proteomes of ME/CFS lymphoblasts versus healthy controls (p = 5.5 × 10−4) (Figure 4C).