Prenatal Diagnosis of β-Thalassemia

Abstract

We investigated a method employing synthetic oligonucleotides for the prenatal diagnosis of β-thalassemia due to a single nucleotide mutation. The β⁰ thalassemia we tested is produced by a nonsense mutation and is commonly found in Sardinia and other parts of the Mediterranean. In this DNA lesion, the glutamine codon CAG at the β³⁹ position is mutated to TAG, which results in a stop codon and premature termination of the β-globin chain. We synthesized two oligonucleotides: one homologous to the normal β^A gene and the other to the β⁰ thalassemia gene at the β³⁹ location. The oligonucleotides were labeled with ³²P and used as hybridization probes for normal and thalassemic DNA. The β^A probe hybridized only to the normal DNA, and the β-thalassemia probe only to thalassemic DNA, thus providing a technique for direct demonstration of the mutation. The method is sensitive enough to be applied directly to DNA that is isolated from uncultured cells obtained from only 20 ml of amniotic fluid as early as the 16th gestational week. (N Engl J Med 1983; 309:284–7.)