Molecular Study and Prenatal Diagnosis of Thalassemia in Taiwan

Abstract

The carrier rates of alpha-thal 1, alpha-thal 2, and beta-thal are 4%, 1% and 1% respectively. If a couple are both the carriers of alpha-thal 1, 25% of the offspring will be affected with homozygous alpha-thal 1, which will result in Hb Bart’s hydrops fetalis and cause various maternal complications. If a couple are both the carriers of beta-thal, 25% of the offspring will be affected with beta-thal major and the patients need life-ling blood transfusion, iron chelation therapy and bone marrow transplantation. This report summarizes our results on thal study in Taiwan. With southern hybridization and various polymerase chain reaction (PCR) techniques, the molecular basis of 832 Chinese Hans with alpha-thal 1 has been characterized. 95.4% had Southeast Asian (SEA) deletion, 2.2% had Thailand (Thai) deletion, and 2.4% had Constant Spring, Quong Sze, or other mutations. 1342 blood samples from five major aboriginal groups, comprising 522 of the Ami, 246 of the Bunun, 227 of the Atayal, 214 of the Paiwan, and 133 of the Yami, were collected for thal study. In the Ami, 43 (8.2%) were alpha-thal 1 carriers (33 with Thai, 9 with SEA, and one with Phil deletion), 43 (8.2%) were alpha-thal 2 carries, one had Hb H disease, and 4 (0.8%) were beta-thal carriers (one each with nonsense 17 and -2 A-G mutation). In the Bunun, one (0.2%) had Thai deletion and 2 (0.4%) were alpha-thal 2 carriers. In the Atayal, one (0.2%) had Phil deletion. In the Paiwan, 7 (3.3%) had alpha-thal 1 (4 with SEA and 3 with Thai deletion) and one (0.5%) had alpha-thal 2. In the Yami, none had either alpha- or beta-thal. In prenatal diagnosis, 624 fetuses at risk for homozygous alpha-thal 1 or severe Hb H disease were studied. Chorionic villus sampling was mainly used to obtain fetal tissue. 170 fetuses were diagnosed as affected. For molecular characterization of beta-thal, 186 unrelated blood-transfusion dependent patients were studied. Southern hybridization, allele-specific oligonucleotide (ASO) hybridization, heteroduplex formation, amplification refractory mutation system (ARMS), artificially created restriction site (ACRS) analysis and direct DNA sequencing have been used. The four most common mutations were IVS-II 654 (C-T)(38.7%), codon 41/42 (deletion of TCTT) (36.6%), -28 (A-G) (6.9%), and nonsense 17 (A-T) (2.8%) mutations. The other mutations detected were A-gamma beta deletion, codon 1 (T-G), codon 27/28 (insertioin of C), Hb E, and codon 71/72 (insertion of A) mutations. The mutations are still unknown in 19 genes. In prenatal diagnosis, 170 fetuses at risk of beta-thal major were studied and 39 fetuses were diagnosed as affected. Three years ago, the Department of Health (DOH) of Taiwan has set up a nation-wide thal screening program. All the pregnant women are encouraged to participate. Couples both with microcytosis are referred to several centers for genotype confirmation and prenatal diagnosis if needed. DOH subsidizes NT 3000 for genotype confirmation of the couple and NT 2000 for prenatal diagnosis. The screening program seems to be running smoothly.