Duplex, triplex and quadruplex PCR for the preimplantation genetic diagnosis (PGD) of cystic fibrosis (CF), an exhaustive approach

Most of cystic fibrosis (CF) pre-implantation genetic diagnosis (PGD) cases described to date are limited to the detection of DeltaF508. Beside this predominant mutation, over 1000 mutations have been identified, rendering the development of a mutation-based PGD protocol impracticable. This is the reason why we, as well as the others, have developed PGD strategies on the basis of the identification of the pathogenic haplotype instead of the mutation(s). In a previous article, we reported the conditions for the co-amplification of two intragenic polymorphic markers and the F508 locus. Here we describe an improved protocol allowing the additional amplification of two new intragenic markers, intron 1 CA repeat (I1CA) and IVS17bTA. This new protocol should, theoretically, allow us to provide a diagnosis to all couples requiring PGD for CF. Using single lymphoblasts, we have tested four different PCR configurations, including one duplex, two triplexes and one quadruplex PCR. All of them gave results compatible with a clinical application. The number of single lymphoblasts tested in each series varied from 89 to 155. PCR efficiency ranged from 95.4 to 100%. A complete haplotype was achieved for 83.2 to 90.7% of the tested cells, with an allele drop out (ADO) rate comprised between 6.0 and 11.6%. We present here three cases that we performed either with the former test (one case using the triplex PCR combining F508, IVS8CA and IVS17bCA) or with the new one (one case using the triplex combining F508, I1CA and IVS17bTA and one case using a quadruplex test). We obtained two single pregnancies.