Examples include the protective effect of heterozygosity for loss of function variants at erythrocyte-specific proteins such as haemoglobin (sickle cell anaemia, thalassaemias), glucose 6-phosphate dehydrogenase, anion exchanger 1 (SLC4A1), Duffy antigen (DARC), ABO blood group variants and several others [17, 19]. The gene discussed is SLC4A1; the disease is thalassemia.