All populations support hemoglobin traits with varying frequencies.
Alpha thalassemia's geographical distribution is similar to that of beta thalassemia. Hemoglobin E, which is the second most common hemoglobin variant in the world, is frequent in people whose ancestry is Cambodian, Laotian, or Thai. In Lao, people from the lowlands, who are closely related to the Thai, have a higher incidence of hemoglobin E than the Hmong from the highlands, who are related to the Chinese. The presence of hemoglobin Constant Spring is a significant factor in predicting clinical severity of Hemoglobin H disease. It is prevalent in Asia and Southeast Asia.