Digital PCR Assay Utilizing In-Droplet Methylation-Sensitive Digestion for Estimation of Fetal cfDNA From Plasma.

Abstract

Objective: Recent guidelines suggest that non-invasive prenatal screening (NIPS) should be offered to all patients with singleton and twin pregnancies. Accurate determination of fetal fraction in cell-free DNA (cfDNA) is vital for reliable NIPS outcomes. We propose a methylation-based approach using droplet digital PCR (ddPCR) and methylation-sensitive restriction enzyme (MSRE) digestion for fetal fraction quantification as an affordable and fast solution.

Method: Following biomarker discovery using early pregnancy placental genomic DNA (gDNA) and cfDNA from non-pregnant female individuals, we designed assays targeting MSRE-compatible regions based on contrasting methylation patterns between maternal and fetal cfDNA. We established a proof-of-concept ddPCR workflow on the Bio-Rad Droplet Digital PCR QX600 instrument.

Results: Testing the fetal fraction assay multiplex on 137 prospective clinical samples demonstrated high concordance with NGS results for both female and male pregnancies as well as with chromosome Y-based calculations for samples with a male fetus. Reproducibility analysis indicated lower variability compared to previously reported NGS performance.

Conclusion: This study showcases the potential of this novel, 6-color, high-multiplex methylation ddPCR panel for accurate measurement of fetal fraction in cfDNA samples. It presents opportunities to integrate such methodology as a standalone measurement to assess the quality of samples undergoing NIPS.