Thalassemia in SouthEast Asia: problems and strategy for prevention and control.

In Southeast Asia alpha-thalassemia, beta-thalassemia, hemoglobin (Hb) E and Hb Constant Spring are prevalent. The gene frequencies of alpha-thalassemia reach 30-40% in Northern Thailand and Laos. beta-Thalassemia gene frequencies vary between 1 and 9%. Hb E is the hallmark of Southeast Asia attaining a frequency of 50-60% at the junction of Thailand, Laos, and Cambodia. Hb Constant Spring gene frequencies vary between 1 and 8%. These abnormal genes in different combinations lead to over 60 different thalassemia syndromes. The four major thalassemic diseases are Hb Bart's hydrops fetalis (homozygous alpha-thalassemia 1), homozygous beta-thalassemia, beta-thalassemia/Hb E and Hb H diseases. The molecular basis of most of these abnormal genes have been recently described. Therefore, it is possible to set a strategy for prevention and control of thalassemia which includes population screening for heterozygotes, genetic counseling and fetal diagnosis with selective abortion of affected pregnancies.