Hemoglobin C
| Hemoglobin C | |
|---|---|
| Specialty | Hematology  |
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]
Symptoms
Most people do not have symptoms. It can cause a mild to moderate enlargement of the spleen, splenomegaly, as well as hemolytic anemia[2] (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 the body, causing mild anemia.[3] Occasionally, jaundice may occur. Some persons with this disease may develop gallstones that require treatment.[4] Continued hemolysis may produce pigmented gallstones, an unusual type of gallstone composed of the dark-colored contents of red blood cells.[5]
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 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. There are fewer acute vaso-occlusive events and therefore fewer sickle cell crises. The peripheral smear demonstrates mostly target cells 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.[6]
People with hemoglobin C trait, or hemoglobin C carriers, have one gene for HbC and one normal gene. Their red blood cells contain both normal hemoglobin A and also hemoglobin C. People with hemoglobin C trait have slightly more hemoglobin A than hemoglobin C in their cells.
Genetics
Hemoglobin C disease is an autosomal recessive disorder that results from the biparental inheritance of the allele that encodes for hemoglobin C.[5] 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.[3]
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.
Diagnosis
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.[4]
Prevention
Genetic counseling may be appropriate for high-risk couples who wish to have a baby.[7]
Treatment
Usually no treatment is needed. Folic acid supplementation may help produce normal red blood cells and improve the symptoms of anemia [7]
Prognosis
Overall, hemoglobin C disease is one of the more benign hemoglobinopathies.[5] 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.[5] People with hemoglobin C disease can expect to lead a normal life.[7]
Epidemiology
Hemoglobin C gene is found in 2-3% of African-Americans[3] while 8% of African-Americans have hemoglobin S (Sickle) gene. Thus Hemoglobin SC disease is significantly more common than Hemoglobin CC disease. Hemoglobin C is found in areas of West Africa, such as Nigeria, where Yorubas live.[8][9][10] The trait also affects people whose ancestors came from Italy, Greece, 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.[2] Hemoglobin C disease is present at birth, though some cases may not be diagnosed until adulthood. Both males and females are affected equally.[5]
References
- ^ "Archived copy". Archived from the original on 2016-02-07. Retrieved 2017-08-31.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help)CS1 maint: archived copy as title (link) - ^ a b Fairhurst, Rick M.; Casella, James F. (2004). "Homozygous Hemoglobin C Disease". New England Journal of Medicine. 350 (26): e24. doi:10.1056/NEJMicm030486. PMID 15215497.
- ^ a b c d "Hemoglobin C Trait". Stjude.org. Retrieved 2015-03-03.
- ^ a b "Updating PubMed Health - National Library of Medicine - PubMed Health". Ncbi.nlm.nih.gov. 2014-11-12. Retrieved 2015-03-03.
- ^ a b c d e Hemoglobin C Disease at eMedicine
- ^ Nagel, Ronald L.; Fabry, Mary E.; Steinberg, Martin H. (2003). "The paradox of hemoglobin SC disease". Blood Reviews. 17 (3): 167–78. doi:10.1016/S0268-960X(03)00003-1. PMID 12818227.
- ^ a b c MedlinePlus Encyclopedia: Hemoglobin C disease
- ^ Akinyanju, Olufemi O. (1989). "A Profile of Sickle Cell Disease in Nigeria". Annals of the New York Academy of Sciences. 565: 126–36. doi:10.1111/j.1749-6632.1989.tb24159.x. PMID 2672962.
- ^ Fairhurst, R. M.; Fujioka, H.; Hayton, K.; Collins, K. F.; Wellems, T. E. (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.
- ^ Edington, G. M.; Lehmann, H. (1956). "36. The Distribution of Haemoglobin C in West Africa". Man. 56: 34. doi:10.2307/2793520. ISSN 0025-1496.
External links
- Hemoglobin+C at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Hemoglobin+C+Disease at the U.S. National Library of Medicine Medical Subject Headings (MeSH)