The hemoglobin E belt at the Thailand-Kampuchea border: ethnic and environmental determinants of hemoglobin E and beta-thalassemia gene frequencies.

The frequencies of the hemoglobin E gene (HBBE) and the beta-thalassemia gene(s) (HBBT) were determined in 890 healthy adult males from three areas at the Thai-Kampuchean border in Northeastern Thailand. The population of the three study areas differs ethnically: area I is inhabited by Khmer-speaking people, area II has an ethnically mixed population (Tai-Lao, Soui and Khmer), and area III is predominantly Lao. In view of the topographic differences in malaria endemicity in the pre-eradication era, the probands from the three study areas were divided into subgroups "hills" and "plains" according to the location of their home villages. The frequencies of HBBT were generally low, but the difference between the HBBE frequencies in the "hills" (0.3295) and "plains" (0.2455) subgroups was highly significant. This is interpreted as environmental effect due to selection by malaria. A "hemoglobin E belt" with HBB*E frequencies between 0.3 and 0.35 extends along the Dangraek mountain chain at the border between Thailand and Kampuchea.