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] Alpha-thalassaemia is common in sub-Saharan Africa, the Mediterranean basin, the Middle East, South Asia, and Southeast Asia; different genetic sub-types have variable frequencies in each of these areas.[19]​​[20][21]

Alpha(0) variants, which can lead to haemoglobin H (Hb H) or alpha-thalassaemia major, are most common in Southeast Asia, southern China, and the Mediterranean; prevalence of carriers is 14% in northern Thailand and 5% to 8.8% in southern China.[11]

The non-deletional mutation Hb Constant Spring is one of the most common variants of alpha-thalassaemia in Southeast Asia and southern China.​[22]

The epidemiology of alpha-thalassaemia in the US reflects this global distribution pattern. The most common form of alpha(+) thalassaemia 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 are more common in the western US, and have increased in prevalence due to increased Asian immigration.[8]

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