Non‐invasive prenatal diagnosis of single gene disorders by paternal mutation exclusion: 3 years of clinical experience

Abstract Objectives Cell‐free fetal DNA (cffDNA) analysis is performed routinely for aneuploidy screening, RhD genotyping or sex determination. Although applications to single gene disorders (SGD) are being rapidly developed worldwide, only a few laboratories offer cffDNA testing routinely as a diagnosis service for this indication. In a previous report, we described a standardised protocol for non‐invasive exclusion of paternal variant in SGD. Three years later, we now report our clinical experience with the protocol. Design Descriptive study. Setting Multi‐centre French. Population Indications for referral included pregnancies at risk of 25% or 50% of paternally inherited SGD, and pregnancies associated with an increased risk of SGD due to a de novo variant, either from strongly suggestive ultrasound findings or from a possible parental germinal mosaicism in the context of a previously affected child. Methods Non‐invasive prenatal diagnosis was performed using custom assays for droplet digital PCR. Feasibility, diagnostic performance and turn‐around time were evaluated. Results Mean time for a new assay design and validation was evaluated at 14 days, and mean result reporting time was 6 days. All referred pathogenic variants could be targeted except one located in a complex genomic region. A result was obtained for every 198 referrals except two. Conclusion This service was successfully implemented as a routine laboratory practice. It has been widely adopted by French clinicians and patients for paternal variant exclusion in various disorders. Tweetable abstract: A robust approach to non‐invasive prenatal exclusion of paternal pathogenic variant in a diagnosis setting.