About one-fifth (65/337; 19.3%) of Duffy-negative individuals of black African ancestry were affected by G6PD deficiency, including heterozygous females whose G6PD phenotype cannot be predicted with accuracy from the genotype due to random X chromosome inactivation unless the enzymatic activity is measured by spectrophotometry or an alternative, reliable field-compatible tool [31,33,100,101]. The gene discussed is G6PD; the disease is hyperinsulinemic hypoglycemia, familial, 4.