Prenatal exclusion of beta thalassaemia major by examination of maternal plasma.

The discovery of the presence of fetal DNA in maternal plasma has provided a new approach for non-invasive prenatal diagnosis. At present, the prenatal diagnosis of beta thalassaemia relies on invasive methods. We designed allele-specific primers and a fluorescent probe for detection of the codon 41/42 (-CTTT) mutation in the beta globin gene from maternal plasma by real-time PCR. The specificity and sensitivity of the allele-specific assay was confirmed by subjecting plasma, buffy coat, and amniotic fluid samples from 100 pregnancies to screening for the mutation. Subsequently, the assay was applied to the prenatal testing of eight fetuses at risk of beta thalassaemia major, the aim being to exclude fetal inheritance of paternally transmitted codon 41/42 mutation. The fetal genotype was completely concordant with conventional analysis and beta thalassaemia major was excluded in two of the pregnancies non-invasively.