HBC

Hemoglobin C (HbC) is a variant of human hemoglobin produced by a point mutation in the beta-globin gene (HBB) that substitutes lysine for glutamic acid at position 6 of the beta chain (Glu6Lys). It is inherited in an autosomal recessive pattern and is most prevalent in West Africa and among populations descended from West African migrations.

Clinical presentation depends on genotype. Individuals with the HbC trait (HbAC) are usually asymptomatic. Homozygous HbC (HbCC) or compound heterozygosity with hemoglobin S (HbSC) or with HbS/HbC can cause a mild to moderate chronic hemolytic anemia, often with splenomegaly and pigment gallstones; vaso-occlusive crises are less common and typically less severe than in sickle cell disease. HbSC can present with intermittent hemolysis and pain episodes, but overall severity is intermediate between HbCC and HbSS.

Pathophysiology involves the tendency of HbC-containing red blood cells to become dehydrated and rigid. In deoxygenated states, HbC can form intracellular crystals, further reducing deformability and promoting hemolysis. Red blood cells may appear as target cells on blood smear, and crystals can sometimes be visible in stained smears.

Laboratory diagnosis relies on hemoglobin electrophoresis or high-performance liquid chromatography, which identify HbC as a distinct band or peak separate from HbA and HbS. A peripheral smear may show target cells and, in some cases, HbC crystals.

Management is generally supportive. Most individuals with HbAC require no specific therapy, while those with HbCC or HbSC may need treatment for anemia or splenomegaly and should receive standard care for complications, including folic acid supplementation and vaccination; prevent and treat infections, and address malaria exposure in endemic areas.