Epidemiology

Alpha-thalassaemia is a common inherited blood disorder; approximately 5% of the global population carry a defective alpha-thalassaemia gene.[16][17]

The worldwide distribution of inherited alpha-thalassaemia corresponds to areas of malaria exposure, suggesting a protective role for alpha-thalassaemia against the more severe manifestations of malaria.[18] Thus, alpha-thalassaemia is common in sub-Saharan Africa, the Mediterranean basin, the Middle East, South Asia, and South-east Asia, and different genetic sub-types have variable frequencies in each of these areas.[19]​​[20][21]

Alpha(0) variants, important because they can lead to haemoglobin H (Hb H) and alpha-thalassaemia major, are most common in Southeast Asia, where the prevalence of carriers reaches 14% in northern Thailand and 5% to 8.8% in southern China.[11]

The non-deletional mutation Hb Constant Spring is also common in Southeast Asia.​[22]

The epidemiology of alpha-thalassaemia in the US reflects this global distribution pattern. The most common form of alpha(+) thalassaemia seen in the US is due to the -alpha(3.7) deletion, a single alpha-globin gene deletion, and is present in approximately 30% of African-Americans.[23] However, even in the homozygous state this disorder will result only in a mild microcytic anaemia. The more serious clinical disorders of Hb H and alpha-thalassaemia major, although found throughout the US today, are more common in the western US and have dramatically increased in prevalence in the past two decades due to increased Asian immigration.[8]

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