of black African descent are at greater risk of prostate cancer than are men of either European or Asian descendant (60% greater incidence and double the mortality compared to Whites). However, the contribution of DARC to this increased risk has been tested in Jamaican males of black African descent. It was found that none of the increased risk could be attributed to the DARC gene. The reason for this increased risk is as yet unknown. Psychiatry The use of the antipsychotic agent clozapine is associated with neutropenia. An increased risk of this side effect has been reported in Duffy null patients. Renal transplantion Antibodies and a cellular response to the Duffy antigen have been associated with renal transplant rejection. Sickle cell anaemia Duffy antigen-negative individuals with sickle cell anaemia tend to sustain more severe organ damage than do those with the Duffy antigen. Duffy-positive patients exhibit higher counts of white blood cells, polynuclear neutrophils, higher plasma levels of IL-8 and RANTES than Duffy-negative patients. Southeast Asian ovalocytosis There is a ~10% increase in Fy expression in Southeast Asian ovalocytosis erythrocytes. Transfusion medicine A Duffy negative blood recipient may have a transfusion reaction if the donor is Duffy positive. Since most Duffy-negative people are of African descent, blood donations from people of black African origin are important to transfusion banks. Transfusion data International Society for Blood Transfusion (ISBT) symbol: FY ISBT number: 008 Gene symbol: FY Gene name: Duffy blood group Number of Duffy antigens: 6 Antibody type Almost entirely IgG. IgG1 usually predominates. IgM does occur but is rare. Antibody behavior Anti-Fya is a common antibody while anti-Fyb is approximately 20 times less common., They are reactive at body temperature and are therefore clinically significant, although they do not typically bind complement. Antibodies are acquired through exposure (pregnancy or history of blood transfusion) and subsequent alloimmunization. They display dosage (react more strongly to homozygous cells versus heterozygous cells). Transfusion reactions Typically mild but may be serious, even fatal. Although these usually occur immediately they may occur after a delay (up to 24 hours). These reactions are usually caused by anti-Fya or anti-Fyb. anti-Fy3 may cause acute or delayed hemolytic transfusion reactions, but only rarely. Anti-Fy5 may also cause delayed hemolytic transfusion reactions. Hemolytic disease of the fetus and newborn Hemolytic disease of the fetus and newborn is typically mild but rarely may be serious. Almost always due to anti-Fya and