Epidemiology

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

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

Alpha(0) variants, important because they can lead to hemoglobin H (Hb H) and alpha-thalassemia 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 nondeletional mutation Hb Constant Spring is also common in Southeast Asia.[22]​​

The epidemiology of alpha-thalassemia in the US reflects this global distribution pattern. The most common form of alpha(+) thalassemia 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 anemia. The more serious clinical disorders of Hb H and alpha-thalassemia 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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