Alpha-thalassemia

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Alpha-thalassemia (?-thalassemia, ?-thalassaemia) is a form of thalassemia involving the genes HBA1 and HBA2. Alpha-thalassemia is due to impaired production of alpha chains from 1, 2, 3, or all 4 of the alpha globin genes, leading to a relative excess of beta globin chains. The degree of impairment is based on which clinical phenotype is present (how many genes are affected).

Video Alpha-thalassemia

Signs/symptoms

The presentation of individuals with alpha-thalassemia consists of:

Maps Alpha-thalassemia

Cause

Alpha-thalassemias are most commonly inherited in a Mendelian recessive manner. They are also associated with deletions of chromosome 16p. Alpha thalassemia can also be acquired under rare circumstances.

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Pathophysiology

The mechanism sees that ? thalassemias results in decreased alpha-globin production, therefore fewer alpha-globin chains are produced, resulting in an excess of ? chains in adults and excess ? chains in newborns. The excess ? chains form unstable tetramers called hemoglobin H or HbH of four beta chains. The excess ? chains form tetramers which are poor carriers of O₂ since their affinity for O₂ is too high, so it is not dissociated in the periphery. Homozygote ?⁰ thalassaemias, where numerous ?₄ but no ?-globins occur at all (referred to as Hb Barts), often result in death soon after birth.

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Diagnosis

Diagnosis of alpha-thalassemia is primarily by laboratory evaluation and molecular diagnosis. Alpha-thalassemia can be mistaken for iron-deficiency anaemia on a full blood count or blood film, as both conditions have a microcytic anaemia. Serum iron and serum ferritin can be used to exclude iron-deficiency anaemia.

Types

Two genetic loci exist for ? globin, thus four alleles are in diploid cells. Two alleles are maternal and two alleles are paternal in origin. The severity of the ?-thalassemias is correlated with the number of affected ?-globin; alleles: the greater, the more severe will be the manifestations of the disease. When noting the genotype, an "?" indicates a functional alpha chain, and '-' a pathological one.

? ?/? ? = normal: '? ?' before the '/' represents one chromosome, and '? ?' after the '/', its homologous chromosome.

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Treatment

Treatment for alpha-thalassemia may consist of blood transfusions, and possible splenectomy; additionally, gallstones may be a problem that would require surgery. Secondary complications from febrile episode should be monitored, and most individuals live without any need for treatment

Additionally, stem cell transplantation should be considered as a treatment (and cure), which is best done in early age. Other options, such as gene therapy, are still being developed.

A study by Kreger et al combining a retrospective review of three cases of alpha thalassemia major and a literature review of 17 cases found that in utero transfusion can lead to favorable outcomes. Successful hematopoietic cell transplantation was eventually carried out in four patients.

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Epidemiology

In terms of epidemiology, worldwide distribution of inherited alpha-thalassemia corresponds to areas of malaria exposure, suggesting a protective role. Thus, alpha-thalassemia is common in sub-Saharan Africa, the Mediterranean Basin, and generally tropical (and subtropical) regions. The epidemiology of alpha-thalassemia in the US reflects this global distribution pattern. More specifically, HbH disease is seen in Southeast Asia and the Middle East, while Hb Bart hydrops fetalis is acknowledged in Southeast Asia only. The data indicate that 15% of the Greek and Turkish Cypriots are carriers of beta-thalassaemia genes, while 10% of the population carry alpha-thalassaemia genes.

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See also

• Beta-thalassemia
• Delta-thalassemia
• Hemoglobinopathy

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References

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Further reading

• Anie, Kofi A; Massaglia, Pia (6 March 2014). "Psychological therapies for thalassaemia". Cochrane Database of Systematic Reviews. John Wiley & Sons, Ltd. doi:10.1002/14651858.cd002890.pub2. Retrieved 15 September 2016. 
• Galanello, Renzo; Cao, Antonio (5 January 2011). "Alpha-thalassemia". Genetics in Medicine. 13 (2): 83-88. doi:10.1097/GIM.0b013e3181fcb468. ISSN 1098-3600. Retrieved 15 September 2016. 

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External links

• "What Are Thalassemias? - NHLBI, NIH". www.nhlbi.nih.gov. Retrieved 15 September 2016. 

Source of article : Wikipedia