Alpha thalassemia
| Alpha-thalassemia | |
|---|---|
 |
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| Alpha-thalassemia inheritance pattern | |
| Classification and external resources | |
| Specialty | hematology |
| ICD-10 | D56.0 |
| ICD-9-CM | 282.43 |
| OMIM | 141800 141850 142310 604131 |
| DiseasesDB | 448 33334 |
| eMedicine | article/955496 |
| MeSH | D017085 |
| GeneReviews | |
Alpha-thalassemia (α-thalassemia, α-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).
The presentation of individuals with alpha-thalassemia consists of:
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.
The mechanism sees that α thalassemias results in decreased alpha-globin production, therefore fewer alpha-globin chains are produced, resulting in an excess of β chains in adults and excess γ chains in newborns. The excess β chains form unstable tetramers called hemoglobin H or HbH of four beta chains. The excess γ 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 α0 thalassaemias, where numerous γ4 but no α-globins occur at all (referred to as Hb Barts), often result in death soon after birth.
Diagnosis of alpha-thalassemia is primarily by laboratory evaluation and haemoglobin electrophoresis. 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.
Two genetic loci exist for α globin, thus four genes are in diploid cells. Two genes are maternal and two genes are paternal in origin. The severity of the α-thalassemias is correlated with the number of affected α-globin; genes: the greater, the more severe will be the manifestations of the disease. When noting the genotype, an "α" indicates a functional alpha chain.
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