[Non-invasive prenatal diagnosis of cystic fibrosis]

Cystic fibrosis (CF) is a frequently fatal autosomal recessive inherited disease affecting around one in 3000 newborns in France, the carrier frequency varying from one in 20 to one in 40 subjects depending on the geographical area. The disease is caused by a chloride channel defect that is attributable to mutations in the gene that encodes the CF transmembrane conductance regulator (CFTR). Approximately, 1200 different mutations have been discovered. Among them, the F508del mutation accounts for 70% of mutated alleles worldwide. Prenatal diagnosis (PND) of inherited monogenic disorders such as CF currently relies on invasive procedures--amniocentesis, chorionic villus sampling (CVS)--which carry a significant risk of miscarriage (from 0.5 to 3%). Several methods have been proposed to enrich circulating fetal cells (CFCs) from blood and use them in PND. However, up to now, no assay has been shown to be reliable enough for routine application in place of the invasive protocols. When combined with laser microdissection, isolation by size of epithelial tumor/trophoblastic cells (ISET) allows mutation analysis of DNA from single cells demonstrated to be fetal (circulating fetal trophoblastic cells [CFTC]) by short tandem repeat (STR) genotyping and uncontaminated with maternal DNA. Application of this protocol to 12 couples at risk of having a child affected by CF has shown, in a blind study, that the new method affords a reliable and safe PND of affected fetus, healthy carrier or normal non carrier fetus. A following prospective blind study has then been performed on 32 couples at risk of having an affected child. For each mother, five or 10 CFTCs have been analyzed with an individual genetic diagnosis performed per CFTC. Results have been obtained in 240 CFTC showing that seven mothers were carrying an affected foetus, with 100% sensitivity and 100% specificity. These results open the way to a multicenter clinical validation trial and to the potential future application of the ISET non invasive approach as a reliable alternative to the invasive PND procedures.