MOLECULAR MECHANISMS OF THALASSEMIA IN THAILAND

PRANEE (WINICHAGOON) FUCHAROEN and SUTHAT FUCHAROEN

ABSTRACT: Thalassemia syndrome, resulting from defective synthesis of globin chains, is the most common genetic disorder in Thailand. -Thalassemia 1 occurs from deletion of both of the duplicated -globin genes. -Thalassemia 2 is the result of a deletion leading to loss of one -globin gene, classified either as leftward (4.2 kb) deletion or rightward (3.7 kb) deletion; the latter is more common in Thai patients. Nondeletion -thalassemia, so far, is rare or absent in the Thai population. Studies of -globin gene cluster in -thalassemia using restriction endonuclease DNA polymorphisms reveal 17 different haplotypes. However, 80.3 %of 158 -thalassemia chromosomes analysed show two common haplotypes, + - - - - - +and + - - - - + +. Point mutations and small deletions or insertions in the nucleotide sequences are responsible for the molecular defects of - thalassemia. In contrast to - thalassemias, a wide area of gene deletion involving the ^A -, - and - globin genes, resulting in (^A ) ^o- thalassemia in two unrelated families, have been identified. Hemoglobin (Hb) E and Hb Constant Spring, the two most common abnormal globin variants, also behave like thalassemia.

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Division of Hematology, Department of Medicine, Faculty of Medicine Siriraj Hospital and The Thalassemia Center, Faculty of Graduate Studies, Mahidol University, Bangkok 10700, Thailand.

Received 27 November 1985