Prenatal diagnosis of β-thalassaemia by reverse dot-blot hybridization

Abstract

Thalassaemia is the most common genetic disease and is a public health problem of Thailand. Prevention and control of β-thalassaemia diseases need accurate diagnosis of carriers and proper genetic counselling. Prenatal diagnosis is needed to prevent birth of the thalassaemic offspring in the couple at risk. This can be performed in the first trimester of pregnancy by DNA analysis using the polymerase chain reaction (PCR). Since there are more than 20 mutations causing β-thalassaemia in Thailand, the point mutation detection by reverse dot-blot allele-specific oligonucleotide (ASO) hybridization was developed using two sets of ASO probes. The first battery of ASO probes has been designed to detect 10 common β-globin gene mutations including codon 26, G→A (Hb E); codons 41/42, -TCTT: codon 17, A→T: IVS 2 nt 654, C→T; IVS 1 nt 1, G→T, IVS 1 nt 5, G→C: codon 19, A→G (Hb Malay), codon 35, C→A: codons 71/72, +A and -28 ATA, A→G. The second set of ASO probes detect 14 uncommon β-thalassaemia mutations. We applied this reverse dot-blot hybridization technique to perform prenatal diagnosis in 105 pregnancies at risk of having severe β-thalassaemia diseases. 36 fetuses (34 per cent) were found to be affected with homozygous β-thalassaemia or β-thalassaemia/Hb E disease in which one was twin pregnancy. The others included 31 fetuses with heterozygous β-thalassaemia, 22 heterozygous Hb E, 1 homozygous Hb E and 16 normal fetuses. The common set of ASO probes detected about 95 per cent of cases which suggests that prenatal diagnosis for β-thalassaemia disease can be easily carried out by this approach.