Hemoglobin C

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Hemoglobin C
Classification and external resources
ICD-10 D58.2
ICD-9-CM 282.7
DiseasesDB 29693
MedlinePlus 000572
eMedicine article/200853
MeSH D006445

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[edit]

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[edit]

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

Combinations with other conditions[edit]

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[edit]

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.[6]

Epidemiology[edit]

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.[7] It is also found in areas of West Africa, such as Ghana, where Yorubas once lived (MAN Volume 56 March 1956 pages 34–36).[8] 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[edit]

Hemoglobin C disease is an autosomal recessive disorder that results from the biparental inheritance of the allele that encodes for hemoglobin C.[6] If both parents are carriers of hemoglobin C, 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 who is a carrier of hemoglobin C 25 percent (1 in 4) chance of having a child without disease and is not a carrier.[3]

Clinical tests[edit]

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[edit]

Usually no treatment is needed. Folic acid supplementation may help produce normal red blood cells and improve the symptoms of anemia [9]

Prognosis[edit]

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.[9]

Prevention[edit]

Genetic counseling may be appropriate for high-risk couples who wish to have a baby.[9]

References[edit]

  1. ^ [1][dead link]
  2. ^ 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. 
  3. ^ a b c d e "Hemoglobin C Trait". Stjude.org. Retrieved 2015-03-03. 
  4. ^ 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. 
  5. ^ a b "Updating PubMed Health - National Library of Medicine - PubMed Health". Ncbi.nlm.nih.gov. 2014-11-12. Retrieved 2015-03-03. 
  6. ^ a b c d e Hemoglobin C Disease at eMedicine
  7. ^ 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. 
  8. ^ 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. 
  9. ^ a b c MedlinePlus Encyclopedia Hemoglobin C disease

External links[edit]