Noninvasive prenatal diagnosis of Down syndrome in samples from Southwest Chinese gravidas using pregnant plasma placental RNA allelic ratio.

OBJECTIVE The purpose of this research was to attempt a preliminary study of noninvasive prenatal diagnosis of Down syndrome in Southwest Chinese gravidas by using the plasma placental RNA allelic ratio. METHODS The genotypes of the single-nucleotide polymorphisms (SNPs) located in the transcribed regions of the gene PLAC4 were detected in population samples collected in Southwest China by using polymerase chain reaction-restriction fragment length polymorphism, and SNPs with a higher heterozygosity were selected. Mass spectrometer analysis was adopted, and cases with the heterozygous SNPs on PLAC4 mRNA in maternal plasma were selected from 29 pregnancies with a euploid fetus and from 21 pregnancies with a trisomy-21 fetus, and then their RNA-SNP allelic ratios were further determined for noninvasive prenatal diagnosis of Down syndrome. RESULTS Of all 50 singleton pregnancies, 37 gravidas were found with at least one heterozygous SNP on PLAC4 mRNA in maternal plasma. Among them, 13 pregnancies with a trisomy-21 fetus were detected by the analysis of the RNA-SNP allelic ratio. CONCLUSION The plasma placental RNA allelic ratio can be used for noninvasive prenatal diagnosis of Down syndrome, if SNPs on PLAC4 mRNA in maternal plasma are heterozygous.