The b -thalassemia gene is common in people of Mediterranean, Middle Eastern, and Asian origin. The severe form of a -thalassemia occurs almost invariably in people from Southeast Asia. Although African Americans and other ethnic groups also carry the a -thalassemia gene, they have the mild form and usually do not suffer any deleterious effects. Homozygous states of these autosomal-recessive diseases cause severe anemia. Patients with sickle cell anemia suffer from frequent painful crises, thrombotic episodes, and infections.
Management consists primarily of treatment of complications.
Prophylactic penicillin therapy prevents death from infections during childhood, and recent studies showed that hydroxyurea therapy decreases the frequency of painful crises and the number of hospital admissions. Although the carriers of these diseases are asymptomatic, they can readily be identified by blood tests. Until there is a cure, prevention can be accomplished by genetic screening and counseling together with prenatal diagnosis. The mutations that give rise to these diseases have largely been defined. Hence it is possible to use DNA tests routinely to diagnosis these conditions.