The anemia in hemoglobin C disease is classified as hemolytic, because it is caused by the destruction of red blood cells. An enlarged spleen, and sometimes jaundice, may also occur. Some persons with this disease may develop gallstones that require treatment. Continued hemolysis may produce pigmented gallstones, an unusual type of gallstone composed of the dark-colored contents of red blood cells. Red blood cell abnormalities
The red blood cells of people with hemoglobin C disease are usually abnormally small (microcytic) with a high mean corpuscular hemoglobin concentration (MCHC). The high MCHC is caused by a decreased concentration of water inside the cells. Target cells, microspherocytes, and HbC crystals can be seen on microscopic examination of blood smears from homozygous patients. Combinations with other conditions
HbC can combine with other abnormal hemoglobins and cause serious hemoglobinopathies. Individuals with sickle cell–hemoglobin C (HbSC), have inherited the gene for sickle cell disease (HbS) from one parent and the gene for hemoglobin C disease (HbC) from the other parent. Since HbC does not polymerize as readily as HbS, there is less sickling in most cases. There are fewer acute vaso-occlusive events and therefore in some cases fewer sickle cell crises. The peripheral smear demonstrates mostly target cells, occasional hemoglobin C crystals, and only a few sickle cells. However, persons with hemoglobin SC disease (HbSC) have more significant retinopathy, ischemic necrosis of bone, and priapism than those with pure SS disease.There are also a few cases of HbC in combination with HbO, HbD and beta thalassemia.
Genetics
Hemoglobin C is produced when a point mutation in the HBB gene causes amino acid substitution of glutamic acid to lysine at the 6th position of the β-globin chain of the hemoglobin. The mutation can be homozygous, occurring on both the chromosomes (alleles), or heterozygous, affecting only one allele. Under heterozygous condition, people are said to have hemoglobin C trait, or as hemoglobin C carriers, and they have one gene for HbC with either one HbA gene or HbS gene. Their red blood cells contain both hemoglobin C and either normal hemoglobin A or hemoglobin S. Hemoglobin C mutation is an autosomal recessive disorder that results from the biparental inheritance of the allele that encodes for hemoglobin C. If both parents are carriers of hemoglobin C, there is a chance of having a child with hemoglobin C disease. Assuming both parents are carriers, there is a 25% chance of having a child with hemoglobin C disease, a 50% chance of having a child who is a carrier of hemoglobin C, and a 25% chance of having a child who is neither a carrier nor affected by hemoglobin C disease.This mutated form reduces the normal plasticity of host erythrocytes causing a hemoglobinopathy. In those who are heterozygous for the mutation, about 28–44% of total hemoglobin (Hb) is HbC, and no anemia develops. In homozygotes, nearly all Hb is in the HbC form, resulting in mild hemolytic anemia, jaundice and enlargement of spleen. Resistance to malaria
Individuals with HbC have reduced risk of P. falciparum malaria infection.