Complete G6PD deficiency is embryonically lethal in mice, but the human G6PD gene has over 200 variants, with the majority being missense mutations resulting in an unstable G6PD enzyme and G6PD deficiency.309 This helps explain why G6PD deficiencies due to these mutations predominantly affect red blood cells: mature red blood cells lack the ability to synthesise new proteins so they cannot replace mutant G6PD, which is more unstable and has a shorter half-life.310,311 The G6PD/NADPH pathway is the sole source of reduced glutathione in red blood cells. This evidence concerns the gene G6PD and G6PD deficiency.