Hemoglobin C Disorders

Hemoglobin C is formed by a single amino acid substitution at the same site as in sickle hemoglobin (codon 6 of the beta globin gene) but with lysine instead of valine substituted for glutamate

Hemoglobin C is nonsickling but may participate in polymer formation in association with hemoglobin S

Homozygous hemoglobin C disease produces a mild hemolytic anemia with

• Splenomegaly

• Mild jaundice

• Pigment (calcium bilirubinate) gallstones

Compared with patients who have homozygous SS disease, those with hemoglobin SC disease have

• Milder hemolytic anemia

• Milder clinical course

• Fewer vaso-occlusive events

• More retinopathy

• More priapism

Peripheral blood smear shows generalized red cell targeting and occasional cells with angular crystals of hemoglobin C

Persons heterozygous for hemoglobin C are clinically normal

Hemoglobin SC disease

• Hematocrit is usually 30–38%, with 5–10% reticulocytes, and compared to SS, fewer irreversibly sickled cells on the blood smear

• Target cells are more numerous than in SS disease

• Hemoglobin electrophoresis shows approximately 45–50% hemoglobin C, 50% hemoglobin S, and no increase in hemoglobin F levels

Folic acid 1 mg orally daily is advised; other treatment is usually necessary only for acute problems

Splenectomy is occasionally required

Cholecystectomy may be needed

Laser eye surgery if retinal neovascularization occurs