G6PD and sickle cell disease: The different geographic distributions of sickle-cell disease, α-thalassemia, glucose-6-phosphate dehydrogenase (G6PD), southeast asian ovalocytosis and the Duffy-negative blood group are examples of the general principle that different populations have selected different genetic variants to protect against Plasmodium infection (see [5], [6], [7] for reviews).