Non-invasive prenatal diagnosis using fetal DNA in maternal plasma: a preliminary study for identification of paternally-inherited alleles using single nucleotide polymorphisms

OBJECTIVES Single nucleotide polymorphism (SNP) with a mutation can be used to identify the presence of the paternally-inherited wild-type or mutant allele as result of the inheritance of either allele in the fetus and allows the prediction of the fetal genotype. This study aims to identify paternal SNPs located at the flanking regions upstream or downstream from the β-globin gene mutations at CD41/42 (HBB:c.127_130delCTTT), IVS1-5 (HBB:c.92+5G>C) and IVS2-654 (HBB:c.316-197C>T) using free-circulating fetal DNA. SETTING Haematology Lab, Department of Biomedical Science, University of Malaya. PARTICIPANTS Eight couples characterised as β-thalassaemia carriers where both partners posed the same β-globin gene mutations at CD41/42, IVS1-5 and IVS2-654, were recruited in this study. OUTCOME MEASURES Genotyping was performed by allele specific-PCR and the locations of SNPs were identified after sequencing alignment. RESULTS Genotype analysis revealed that at least one paternal SNP was present for each of the couples. Amplification on free-circulating DNA revealed that the paternal mutant allele of SNP was present in three fcDNA. Thus, the fetuses may be β-thalassaemia carriers or β-thalassaemia major. Paternal wild-type alleles of SNP were present in the remaining five fcDNA samples, thus indicating that the fetal genotypes would not be homozygous mutants. CONCLUSIONS This preliminary research demonstrates that paternal allele of SNP can be used as a non-invasive prenatal diagnosis approach for at-risk couples to determine the β-thalassaemia status of the fetus.