Distribution of thalassemias and associated hemoglobinopathies identified by prenatal diagnosis in Taiwan

BackgroundHemoglobin (Hb) gene disorders are common hereditary disorders in Taiwan, and α- and β-thalassemias are among the well-known Hb disorders here. Our study provides a primary reference for designing a locally relevant antenatal diagnostic test to control the spread of thalassemia.MethodsBetween 1998 and 2011, prenatal diagnoses for identifying thalassemia and hemoglobinopathies were performed on 1240 fetuses at risk for α-hydrops and β-thalassemia major.ResultsOf 1240 specimens analyzed, 1082 (87%) were obtained by amniocentesis; 125 (10%), by chorionic villus sampling; and 33 (3%), by cordocentesis. Prenatal diagnoses revealed that 21.5% of these fetuses as thalassemia major (including α-thalassemia hydrops, β-thalassemia major, and Hb E/β-thalassemia); 50.2%, for thalassemia minor (include α-thalassemia carrier, β-thalassemia carrier, and α-thalassemia combined β-thalassemia carrier); and 28.3% for normal type (include non-α, β-thalassemia). The most common α-hydrops were SEA (Southeast Asian) and Philippine type (frequencies of 74.91 and 5.24%, respectively). The frequency of the IVS-II-654 combined codons 41/42 mutation, the most common β-thalassemia major mutation in this region, was 5.24%. Two fetuses were found with E/β-thalassemia (HbE/IVS-II-654 and HbE/codons 41/42, respectively). Since 1993, Taiwan's Department of Health adopted a national program for screening pregnancies to control spread of thalassemia. In the last 10 years, less than 3 such cases have occurred per year. After 2003, this number was 0 for a total of 4 years (2003, 2004, 2007, and 2008).ConclusionIn Taiwan, incidence and frequency of thalassemia genotypes were similar to those previously reported. The national program for screening pregnancies to control spread of thalassemia that resulted in a marked decline in the number of newborns with thalassemia major. Interestingly, prenatal diagnoses revealed 21.5% for thalassemia major, 50.2% for thalassemia minor, 28.3% normal comparison of thalassemia type distribution showed normal type increasing by 13.2% and major type decreasing by 14%. This unique and significant finding needs further clinical studies and discussion to explain such a phenomenon.