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

Alpha(0) variants, which can lead to hemoglobin H (Hb H) or alpha-thalassemia 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 nondeletional mutation Hb Constant Spring is one of the most common variants of alpha-thalassemia in Southeast Asia and southern China.[22]​​

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

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