Single-tube genotyping using a solid-phase method that combines α-phosphorothioate-mediated primer extension and ExoIII: Proof of concept with the F508del cystic fibrosis diagnosis

Detection of single nucleotide polymorphisms (SNPs) and of mutations is of importance in the field of genetics, biomedical research and in vitro diagnosis. We report here a genotyping procedure that can be virtually applied to any locus within a genome: it uses α-phosphorothioate deoxynucleotides in a primer-extension step followed by an ExoIII treatment. Non-extended primers are hydrolyzed whereas extended primers resist this treatment, indicating which nucleotide has been incorporated, i.e. the genotype of the locus. A 3-bp deletion in the CFTR gene (F508del, the most prevalent mutation involved in cystic fibrosis) was used as a model, in a single-tube procedure for each nucleotide to be tested. Human genomic DNA samples were correctly genotyped in less than 3 h by a solid-phase PCR followed by primer extension, ExoIII treatment and an ELISA-like detection method. The same principle (primer extension with α-phosphorothioate deoxynucleotide, ExoIII treatment) should also be combined with other detection systems such as gel or capillary electrophoresis, mass spectrometry or DNA chips.