Definition: The term Inherited Blood Disorders (IBDs) encompasses a large number of genetically inherited disorders of the blood. Three IBDs are shown here: sickle hemoglobin (HbS), glucose-6-phosphate dehydrogenase (G6PD) deficiency, and thalassemia. They, along with Duffy antigen (see below), are of interest because of their relationship with malaria. HbS is a variant of normal adult hemoglobin that results in red blood cells (RBCs) taking on an abnormal sickle shape under conditions of low oxygen concentration or oxidative stress. When HbS is inherited from only one parent (genotype HbAS, sickle trait) the individual is usually asymptomatic, but if HbS is inherited from both parents (genotype HbSS), the individual suffers a severe disorder (sickle cell disease). The map opposite (top left) shows the estimated world-wide distribution of HbS allele frequency. G6PD is an enzyme that is essential in the metabolism of RBCs. G6PD deficiency is an X-linked genetic disorder and, although most people are asymptomatic, the most common clinical manifestation is neonatal jaundice or acute hemolytic anemia (AHA). The map opposite (bottom left) shows the estimated prevalence of G6PD deficiency in males (where male prevalence is not available, total prevalence is used). Thalassemia causes abnormal hemoglobin molecules and RBCs with a shortened life span. Their clinical symptoms range from asymptomatic to severe anemia and death. The two major forms of thalassemia are termed alpha and beta, based on the globin chain affected. The Duffy antigen is a protein on the surface of RBCs that acts as a receptor for several signaling proteins but which also binds certain malaria species. Duffy antigen status is inherited but it is not an IBD since Duffy status itself does not result in any medical condition.
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