Circulating placental RNA in maternal plasma is associated with a preponderance of 5' mRNA fragments: implications for noninvasive prenatal diagnosis and monitoring.

BACKGROUND The molecular characteristics of placental RNA circulating in maternal plasma are unknown. We investigated the integrity of circulating placental RNA in maternal plasma and tested the relevance of plasma RNA integrity for noninvasive prenatal diagnosis. METHODS Six different placental transcripts and mRNA of the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were quantified for the 5' and 3' regions in maternal plasma by 1-step real-time reverse transcription-PCR (RT-PCR) assays. This quantitative strategy was validated by 2-step RT-PCR and serial dilution experiments. The rates of detection by the 5' and 3' assays for the beta-subunit of human chorionic gonadotropin (beta hCG) were assessed in maternal plasma samples collected from different gestational periods. RESULTS For 5 of the 7 genes, the plasma mRNA concentrations measured by the 5' amplicons were significantly higher than those measured by the corresponding 3' amplicons. Every transcript under study demonstrated a higher rate of detection in the 5' assay than in the 3' assay in maternal plasma. In particular, the detection rate of beta hCG mRNA in maternal plasma was increased throughout gestation when the 5' assay was used. CONCLUSIONS Circulating placental RNA is associated with a preponderance of 5' mRNA fragments in maternal plasma. Apart from its intrinsic biological interest, this information could have important implications for the development of new assays targeting fetal RNA markers for noninvasive prenatal diagnosis and monitoring.