Prenatal diagnosis of α- and β-thalassaemias in Singapore—current status

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Abstract
Prenatal diagnosis was performed in 31 pregnancies where the fetuses were at risk for either homozygous α°- or β-thalassaemia. First-trimester prenatal diagnosis by DNA analysis using chorionic villi was carried out for 17 pregnancies at risk for homozygous α°-thalassaemia. The α-globin genes in fetal DNA were detected by gene mapping using restriction endonuclease mapping and hybridization with cloned α-globin probe. Homozygous α°-thalassaemia was detected in four fetuses and the results were subsequently confirmed by electrophoresis of the cord blood where only Hb Barts was detected. Prenatal diagnosis for β-thalassaemia was carried out by globin chain biosynthesis using fetal blood at 18–20 weeks' gestation. Using carboxymethyl (CM) sepharose chromatography, homozygous β-thalassaemia was predicted in six pregnancies, and one fetus carried Hb E-β thalassaemia. The seven pregnancies were terminated and globin chain analysis using cord blood confirmed the prenatal diagnoses. The remaining seven fetuses were diagnosed as either normal or β-thalassaemia carriers. Using DNA analysis and globin chain biosynthesis for prenatal diagnosis of homozygous α°- and β- thalassaemia, a 100% correlation was achieved with fetuses predicted to possess the homozygous condition.