Hemoglobin C

Hemoglobin C (abbreviated as Hb C or HbC) is an abnormal hemoglobin in which substitution of a glutamic acid residue with a lysine residue at the 6th position of the β-globin chain has occurred (E6K substitution).^[1]

Clinical significance

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

Presentation

Target cells, microspherocytes and HbC crystals are found in a blood smear from a homozygous patient.

Combinations with other conditions

Individuals with sickle cell–hemoglobin C (HbSC), have the gene for HbS inherited from one parent and the gene for HbC is inherited from the other parent: they are "heterozygous". Since HbC does not polymerize as readily as HbS, there is less sickling (fewer sickle cells). The peripheral smear demonstrates mostly target cells and only a few sickle cells. There are fewer acute vaso-occlusive events. However, persons with hemoglobin SC disease (HbSC) have more significant retinopathy, ischemic necrosis of bone, and priapism than those with pure SS disease.^[2] People with hemoglobin C trait have red blood cells that have normal hemoglobin A and an abnormal hemoglobin. The abnormal hemoglobin is called hemoglobin C. People with hemoglobin C trait have slightly more hemoglobin A than hemoglobin C. People with Hemoglobin C trait do not have health problems related to having the trait. People with hemoglobin C do not have Hemoglobin C disease or sickle cell disease. They cannot develop these diseases later in life. They can pass hemoglobin C trait to their offspring.^[3] Individuals who carry the hemoglobin C trait can have a child with Hemoglobin C disease or Hemoglobin SC disease. Hemoglobin C disease is not a form of sickle cell disease.

Symptoms

Most people do not have symptoms. It can cause a mild to moderate enlargement of the spleen, splenomegaly, as well as hemolytic anemia ^[4] (which is the form of anemia due to abnormal breakdown of red blood cells prematurely). Too much hemoglobin C can reduce the number and size of red blood cells in your body, causing mild anemia.^[3] Occasionally, jaundice may occur. Some persons with this disease may develop gallstones that require treatment.^[5] Continued hemolysis may produce pigmented gallstones, an unusual type of gallstone composed of the dark-colored contents of red blood cells. The cause of pigmented gallstones is uncertain.^[6]

Epidemiology

Hemoglobin C gene is found in 2-3% of US Blacks while 8% of US Blacks have hemoglobin S (Sickle) gene. Thus Hemoglobin SC disease is significantly more common than Hemoglobin CC disease. Hemoglobin C is found predominantly in Yorubas (A profile of sickle cell disease in Nigeria By O.O Akinyanju, Department of Medicine University of Lagos). It is also found in areas of West Africa, such as Ghana, where Yorubas once lived (MAN Volume 56 March 1956 pages 34–36).^[7] About 1 out of every 40 African-Americans has hemoglobin C trait.^[3] The trait also affects people whose ancestors came from Italy, Greece, Africa, Latin America, and the Caribbean region.^[3] However, it is possible for a person of any race or nationality to have hemoglobin C trait. In terms of geographic distribution, the hemoglobin C allele is found at the highest frequencies in West Africa, where it has been associated with protection against malaria.^[4] Hemoglobin C disease is present at birth, though some cases may not be diagnosed until adulthood. Both sexes, male and female, are affected equally.^[6]

Heredity of Hemoglobin C Disease

Hemoglobin C disease is an autosomal recessive disorder that results from the biparental inheritance of the gene that encodes for hemoglobin C.^[6] If both parents have hemoglobin C trait, there is a chance of having a child with hemoglobin C disease. These are the possible outcomes with each pregnancy. 25 percent (1 in 4) chance of having a child with hemoglobin C disease 50 percent (1 in 2) chance of having a child with hemoglobin C trait 25 percent (1 in 4) chance of having a child without trait or disease.^[3]

Clinical Tests

Physical Examination may show an enlarged spleen. Tests that may be done include: Complete Blood Count (CBC), Hemoglobin electrophoresis, Peripheral blood smear, and Blood hemoglobin.^[5]

Treatment

Usually no treatment is needed. Folic acid supplementation may help produce normal red blood cells and improve the symptoms of anemia ^[8]

Prognosis

Overall, hemoglobin C disease is one of the more benign hemoglobinopathies.^[6] Mild-to-moderate reduction in RBC lifespan may accompany from mild hemolytic anemia. Individuals with hemoglobin C disease have sporadic episodes of musculoskeletal (joint) pain.^[6] People with hemoglobin C disease can expect to lead a normal life.^[8]

Prevention

Genetic counseling may be appropriate for high-risk couples who wish to have a baby.^[8]

References

• (2007) Olubunmi A.O. The Rise and Fall of The Yoruba Race 10,000BC-1960AD ISBN 978-2457-38-8

1. ↑ Hemoglobin C (HBB, GLU6LYS)
2. ↑ Nagel RL, Fabry ME, Steinberg MH (September 2003). "The paradox of hemoglobin SC disease". Blood Rev. 17 (3): 167–78. doi:10.1016/S0268-960X(03)00003-1. PMID 12818227. Retrieved 2009-02-24. 
3. ↑ 3.0 3.1 3.2 3.3 3.4 http://www.stjude.org/stjude/v/index.jsp?vgnextoid=f1b0db6324d6f110VgnVCM1000001e0215acRCRD
4. ↑ 4.0 4.1 http://www.nejm.org/doi/full/10.1056/NEJMicm030486
5. ↑ 5.0 5.1 http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001598/
6. ↑ 6.0 6.1 6.2 6.3 6.4 http://emedicine.medscape.com/article/200853-overview
7. ↑ Fairhurst RM, Fujioka H, Hayton K, Collins KF, Wellems TE (April 2003). "Aberrant development of Plasmodium falciparum in hemoglobin CC red cells: implications for the malaria protective effect of the homozygous state". Blood 101 (8): 3309–15. doi:10.1182/blood-2002-10-3105. PMID 12480691. 
8. ↑ 8.0 8.1 8.2 http://www.nlm.nih.gov/medlineplus/ency/article/000572.htm

External links

• Hemoglobin C at the US National Library of Medicine Medical Subject Headings (MeSH)
• Hemoglobin C Disease at the US National Library of Medicine Medical Subject Headings (MeSH)