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Alpha-thalassemia (α-thalassemia, α-thalassaemia) is an inherited blood disorder and a form of thalassemia. Thalassemias are a group of inherited blood conditions which result in the impaired production of hemoglobin , the molecule that carries oxygen in the blood. [ 4 ]
Alpha-thalassemia (α-thalassemia) is defined by a lack of α-globin chain production in hemoglobin, and those who carry a mutation impacting the α-globin chain on only one chromosome are considered to have a “silent” α-thalassemia whereas, if the mutation is on both then it is considered an α-thalassemia trait.
Alpha thalassemia is caused by deficient production of the alpha globin component of hemoglobin, while beta thalassemia is a deficiency in the beta globin component. [7] The severity of alpha and beta thalassemia depends on how many of the four genes for alpha globin or two genes for beta globin are faulty. [2]
Normal levels range from 2.1-3.2%, but in the beta-thalassemia disorder, the levels increase to 3.5-6.0%. Additionally, individuals with beta-thalassemia exhibit a high red cell count and low hemoglobin levels. [3] Individuals that express lower levels of hemoglobin A2, have the a 0-thalassemia trait or homozygous gene for a +-thalassemia. [2]
Alpha Gene Arrangement Functioning α-genes Inheritance Hgb G, % Clinical Presentation uncomplicated G trait, no thalassemia: αG α/α α: 4: Mediterranean: 20-25: No defect alpha thal 2 with trans G trait: α -/αG – or – α/αG – 2: Mediterranean: 35-45: Microcytic alpha thal 2 trait, G trait: α3.7G/α α: 3: African American: 25-35 ...
It is the most common nondeletional alpha-thalassemia mutation associated with hemoglobin H disease. [1] The quantity of hemoglobin in the cells is low because the messenger RNA is unstable and some is degraded prior to protein synthesis. Another reason is that the Constant Spring alpha chain protein is itself unstable.
Though only definitively diagnosable by genetic sequence testing, including a G band analysis, ATR-16 syndrome may be diagnosed from its constellation of symptoms. It must be distinguished from ATR-X syndrome, a very similar disease caused by a mutation on the X chromosome, and cases of alpha-thalassemia that co-occur with intellectual disabilities with no underlying genetic relationship.
Alpha thalassemia patients have partial or complete defects in alpha globin production, leading to a relative abundance of beta globin chains in the cell. These excess beta globin chains aggregate to form HbH , which has decreased solubility and precipitates in the red blood cell cytoplasm . [ 10 ]