Hemoglobin E or haemoglobin E (HbE) is an abnormal hemoglobin with a single point mutation in the β chain. At position 26 there is a change in the amino acid, from glutamic acid to lysine. Hemoglobin E has been one of the less well known variants of normal hemoglobin. It is very common in Southeast Asia but has a low frequency amongst other races. HbE can be detected on electrophoresis.
The βE mutation affects β-gene expression creating an alternate splicing site in the mRNA at codons 25-27 of the β-globin gene. Through this mechanism, there is a mild deficiency in normal β mRNA and production of small amounts of anomalous β mRNA. The reduced synthesis of β chain may cause β-thalassemia. Also, this hemoglobin variant has a weak union between α- and β-globin, causing instability when there is a high amount of oxidant.
Hemoglobin E disease (EE)
Hemoglobin E disease results when the offspring inherits the gene for HbE from both parents. At birth, babies homozygous for the hemoglobin E allele do not present symptoms due to HbF (fetal hemoglobin) they still have. In the first months of life, fetal hemoglobin disappears and the amount of hemoglobin E increases, so the subjects start to have a mild β-thalassemia. People who are heterozygote for hemoglobin E (one normal allele and one abnormal allele) do not show any symptoms (there is usually no anemia or hemolysis). Subjects homozygous for the hemoglobin E allele (two abnormal alleles) have a mild hemolytic anemia and mild splenomegaly.
Hemoglobin E trait: heterozygotes for HbE (AE)
Heterozygous AE occurs when the gene for haemoglobin E is inherited from one parent and the gene for hemoglobin A from the other. This is called hemoglobin E trait, and it is not a disease. People who have hemoglobin E trait (heterozygous) are asymptomatic and their state does not usually result in health problems. They may have a low mean corpuscular volume (MCV) and very abnormal red blood cells (target cells). Its clinical relevance is exclusively due to the potential for transmitting E or β-thalassemia.
Heterozygotes for HbE (SE)
Compound heterozygotes with hemoglobin sickle E disease result when the gene of hemoglobin E is inherited from one parent and the gene for hemoglobin S from the other. As the amount of fetal hemoglobin decreases and hemoglobin S increases, a mild hemolytic anemia appears in the early stage of development.
People who have hemoglobin E/β-thalassemia have inherited one gene for hemoglobin E from one parent and one gene for β-thalassemia from the other parent. Hemoglobin E/β-thalassemia is a severe disease, and it still has no universal cure. It affects more than a million people in the world. The consequences of hemoglobin E/β-thalassemia when it is not treated can be heart failure, the enlargement of the liver, problems in the bones, etc.
There is a variety of genotypes depending on the interaction of HbE and α-thalassemia. The presence of the α-thalassemia reduces the amount of HbE usually found in HbE heterozygotes. In other cases, in combination with certain thalassemia mutations, it provides an increased resistance to malaria (P. falciparum).
Hemoglobin E is most prevalent in Southeast Asia (Thailand, Myanmar, Cambodia, Laos, Vietnam), where its prevalence can reach 30 or 40%, and North-East India, where in certain areas carrier rates reach 60% of the population. In Thailand the mutation can reach 50 or 70%, and it is higher in the North-East of the country. It is also found in China, the Philippines, Turkey, Nepal, Sri Lanka, Pakistan, etc. The mutation is estimated to have arisen within the last 5,000 years. In Europe there have been found cases of families with hemoglobin E, but in these cases, the mutation differs from the one found in South-East Asia. This means that there may be different origins of the βE mutation.
- Hemoglobin E fact sheet from the Washington State Department of Health
- American Society of Hematology Educational Program profile of Hemoglobin E disorders
- Orphanet Encyclopedia entry for Hemoglobin E
- Hemoglobin E in Europeans
- Chernoff AI, Minnich V, Nanakorn S, et al. (1956). "Studies on hemoglobin E. I. The clinical, hematologic, and genetic characteristics of the hemoglobin E syndromes.". J Lab Clin Med 47 (3): 455–489. PMID 13353880.
- Vichinsky E (2007). "Hemoglobin E Syndromes.". Hematology Am Soc Hematol Educ Program: 79–83. doi:10.1182/asheducation-2007.1.79. PMID 18024613.
- Bachir, D; Galacteros, F (November 2004), Hemoglobin E disease., Orphanet Encyclopedia, retrieved January 13, 2014
- Hemoglobin E Trait, University of Rochester Medical Center, retrieved January 13, 2014
- Ohashi et al. (2004). "Extended linkage disequilibrium surrounding the hemoglobin E variant due to malarial selection". Am J Hum Genet 74 (6): 1189–1208. doi:10.1086/421330. PMC 1182083. PMID 15114532. Free full text
- Kazazian HH, JR., Waber PG, Boehm CD, Lee JI, Antonarakis SE, Fairbanks VF. (1984). "Hemoglobin E in Europeans: Further Evidence for Multiple Origins of the βE-Globin Gene.". Am J Hum Genet 36 (1): 212–217. PMC 1684388. PMID 6198908. Free full text
- Bain, Barbara J (June 2006). Blood cells: a practical guide (4th ed.). Wiley-Blackwell. ISBN 978-1-4051-4265-6.