G6PD and G6PD deficiency: G6PD deficiency has also been linked with mental illnesses in adults in some case reports/series,[21, 22] and genetic linkage studies[23–25] but not all.[26–30] Genetic studies are less open to confounding than most observational studies, nevertheless the evidence concerning effects of G6PD is limited and potentially biased by design flaws, such as inappropriate selection of controls in case-control studies.