G6PD and G6PD deficiency: Young red blood cells have high G6PD enzyme activity, which declines more rapidly in individuals with G6PDd enzyme variants versus G6PD-normal individuals, and more quickly with “severe” variants (e.g., G6PD Mediterranean) versus those that confer “mild-to-moderate” G6PD deficiency (e.g., G6PD A−, G6PD Mahidol).