1) A couple underwent preimplantation genetic diagnosis (PGD) for Dyskeratosis Congenita caused by a mutation in the RTEL1 gene, as they previously had an affected child. 2) Conventional PGD using short tandem repeat (STR) markers near the gene found high rates of allele drop out and no results for some embryos. 3) Reanalysis using quantitative PCR (qPCR) of single nucleotide polymorphisms (SNPs) closer to the mutation found the STR-based method misdiagnosed 21% of embryos due to undetected recombinations between the STRs and mutation. 4) qPCR allowed simultaneous analysis of multiple linked SNPs and the mutation, avoiding