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beta thalassemia
Beta thalassemias (β thalassemias) are a group of inherited blood disorders. They are caused by reduced or absent synthesis of the beta chains of hemoglobin that result in variable outcomes ranging from severe anemia to clinically asymptomatic individuals. Global annual incidence is estimated at 1 in 100,000. Beta thalassemia (β thalassemia) is a form of thalassemia caused by mutations in the HBB gene on chromosome 11, inherited in an autosomal recessive fashion. The severity of the disease depends on the nature of the mutation.
HBB blockage over time leads to decreased Beta-chain synthesis. The body’s inability to construct new Beta-chains leads to the underproduction of HBA. Reductions in HBA available overall to fill the red blood cells in turn leads to microcytic anemia. Microcytic anemia ultimately develops in respect to inadequate HBB for sufficient red blood cell functioning. Due to this factor, the patient must undergo a blood transfusion for survival to make up for the blockage in the Beta-chains. Repeated blood transfusions lead to build-up of iron overload ultimately resulting in iron toxicity. This iron toxicity produces myocardial siderosis and heart failure leading to the patient’s death.
== Signs and symptoms ==
Three main forms have been described: thalassemia major, thalassemia intermedia and thalassemia minor. All people with thalassemia are susceptible to health complications that involve the spleen (which is often enlarged and frequently removed) and gallstones. These complications are mostly found in thalassemia major and intermedia patients.Individuals with beta thalassemia major usually present within the first two years of life with severe anemia, poor growth and skeletal abnormalities during infancy. Untreated thalassemia major eventually leads to death, usually by heart failure; therefore, birth screening is very important.
Excess iron causes serious complications within the liver, heart and endocrine glands. Severe symptoms include liver cirrhosis, liver fibrosis and in extreme cases, liver cancer. Heart failure, growth impairment, diabetes and osteoporosis are life-threatening contributors brought upon by TM. The main cardiac abnormalities seen to have resulted from thalassemia and iron overload include left ventricular systolic and diastolic dysfunction, pulmonary hypertension, valveulopathies, arrhythmias and pericarditis. Increased gastrointestinal iron absorption is seen in all grades of beta thalassemia and increased red blood cell destruction by the spleen due to ineffective erythropoiesis further releases additional iron into the bloodstream.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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