δ-Hemoglobinopathies in Thailand: screening, molecular basis, genotype-phenotype interaction, and implication for prevention and control of thalassemia.

The δ-globin gene defects are clinically silent but interaction with β-thalassemia can lead to a misdiagnosis of β-thalassemia carrier. We report an extensive molecular characterization of δ-hemoglobinopathies in Thailand. Study was done on 32,108 subjects, encountered at the thalassemia screening. Six different approaches based on the reduced Hb A2 or appearance of Hb A2-derivative were established for selective recruitment of subjects. Among 32,108 subjects, a total of 296 subjects were suspected of having δ-globin gene defects. Of these 296 subjects, Hb and DNA analyses identified δ-hemoglobinopathies with 10 different mutations in 34 (0.11%) of them. These included a novel mutation, [δCD30(AGG>GGG) (n = 1)], 5 previously undescribed in Thailand, [δ-44(G>A) (n = 7), Hb A2-Troodos (n = 5), δIVSII-897(A>C) (n = 4), δ-68(C>T) (n = 2), and Hb A2-Indonesia (n = 1)], and 4 mutations previously found in Thailand, [Hb A2-Melbourne (n = 9), δ-77(T>C) (n = 3), Hb A2' (n = 1), and Hb A2-Kiriwong (n = 1)]. Genetic heterogeneities seen included interactions of δ-globin gene defects with heterozygous Hb E, β-thalassemia, α-thalassemia, and in cis locations of the Hb A2-Troodos and Hb E mutations found for the first time. Rapid identification methods of these δ-globin gene mutations were developed. The results should prove useful to a prevention and control program of hemoglobinopathies in the region.