Molecular analysis of beta-thalassemia in South Vietnam

Abstract

In Vietnam, the carrier rate for beta-thalassemia varies from 1.5% to 25% depending on the ethnic groups of the population. The molecular basis of beta-thalassemia in South Vietnam was studied in 50 unrelated beta-thalassemia patients. Of these, 31 had beta-thalassemia/Hb E, 18 were homozygous for beta-thalassemia, and 1 carried the beta-thalassemia trait. The majority of the patients were Kinh, four were Chinese, and two were Kinh-Chinese. All had severe anemia and received blood transfusions regularly, every 1-3 months. Hepatosplenomegaly was found in all patients, and splenectomy had been done in six patients. Normal alpha-globin genotype (alpha alpha/alpha alpha) was found in all subjects. Reverse dot-blot hybridization using oligonucleotide probes specific for Southeast Asian mutations can detect beta-thalassemia in 60 chromosomes in addition to 31 chromosomes with beta(E) mutation. Excluding the beta(E) gene, six previously reported Thai and Chinese beta-thalassemia mutations were found, including codons 41/42 (-TCTT) 35.3%, codon 17 (A-->T) 25.0%, -28 (A-->G) 7.3%, codons 71/72 (+A) 7.3%, IVS-II nt 654 (C-->T) 7.3%, and IVS-I nt 1 (G-->T) 6.0%. The Vietnamese frameshift mutation at codon 95 (+A) was detected by ARMS in seven chromosomes (10.3%). DNA polymorphism of the beta-globin gene cluster carrying the codon 95 mutation was - + - - - - - + for (G)gamma/XmnI, epsilon/HincII, (G)gamma/HindIII, (A)gamma/HindIII, psi beta/HincII, 3' psi beta/HincII, beta/AvaII, and 3'beta/BamHI, respectively. The remaining mutation detected by the gap PCR was a large deletion known as the Chinese (G)gamma((A)gamma delta beta)(0)-thalassemia. The two most common mutations were the frameshift at codons 41/42 (-TCTT) and the nonsense mutation in codon 17 (A-->T). Thus beta-thalassemia mutations in South Vietnam is similar to the previous report from the North, although at different frequencies. This result will help to establish a center for prenatal diagnosis and for prevention and control of thalassemia in Vietnam.