The improvement of the best practice guidelines for preimplantation genetic diagnosis of cystic fibrosis : toward an international consensus

Cystic fibrosis (CF) is one of the most common indications for preimplantation genetic diagnosis (PGD) for single gene disorders, giving couples the opportunity to conceive unaffected children without having to consider termination of pregnancy. However, there are no available standardized protocols, so that each center has to develop its own diagnostic strategies and procedures. Furthermore, reproductive decisions are complicated by the diversity of disease-causing variants in the CFTR (cystic fibrosis transmembrane conductance regulator) gene and the complexity of correlations between genotypes and associated phenotypes, so that attitudes and practices toward the risks for future offspring can vary greatly between countries. On behalf of the EuroGentest Network, eighteen experts in PGD and/or molecular diagnosis of CF from seven countries attended a workshop held in Montpellier, France, on 14 December 2011. Building on the best practice guidelines for amplification-based PGD established by ESHRE (European Society of Human Reproduction and Embryology), the goal of this meeting was to formulate specific guidelines for CF-PGD in order to contribute to a better harmonization of practices across Europe. Different topics were covered including variant nomenclature, inclusion criteria, genetic counseling, PGD strategy and reporting of results. The recommendations are summarized here, and updated information on the clinical significance of CFTR variants and associated phenotypes is presented

Preimplantation Genetic Testing for Monogenic Disorders

Preimplantation genetic testing (PGT) has evolved into a well-established alternative to invasive prenatal diagnosis, even though genetic testing of single or few cells is quite challenging. PGT-M is in theory available for any monogenic disorder for which the disease-causing locus has been unequivocally identified. In practice, the list of indications for which PGT is allowed may vary substantially from country to country, depending on PGT regulation. Technically, the switch from multiplex PCR to robust generic workflows with whole genome amplification followed by SNP array or NGS represents a major improvement of the last decade: the waiting time for the couples has been substantially reduced since the customized preclinical workup can be omitted and the workload for the laboratories has decreased. Another evolution is that the generic methods now allow for concurrent analysis of PGT-M and PGT-A. As innovative algorithms are being developed and the cost of sequencing continues to decline, the field of PGT moves forward to a sequencing-based, all-in-one solution for PGT-M, PGT-SR, and PGT-A. This will generate a vast amount of complex genetic data entailing new challenges for genetic counseling. In this review, we summarize the state-of-the-art for PGT-M and reflect on its future

HLA typing and preimplantation genetic diagnosis

Typing of human leukocyte antigens (HLA) on preimplantation embryos is legally allowed and ethically accepted in Belgium. The 'Vrije Universiteit Brussel' (VUB) has five years of experience with technical and clinical aspects of HLA typing on single cells. Setting up and running a programme for HLA typing is labour intensive, in particular when it has to be combined with preimplantation genetic diagnosis (PGD) for distinct inherited genetic diseases, and time is always pressing because of the need for transplantation of the affected sibling. A general technique for HLA typing using short tandem repeats (STRs) linked to the HLA locus in multiplex PCR has been developed at our centre. At present, the overall clinical success rate is low: the ongoing pregnancy rate per oocyte retrieval cycle is 9.8%. This is not due to the technique because a conclusive HLA diagnosis can be assured in 91.9% of the embryos. The low success rate is correlated with a low transfer rate per cycle (35.5%). This is due to the genetic constitution of the embryos (in theory 1/4 for HLA, 1/8 for HLA in combination with sexing for X-linked recessive diseases and 3/16 for HLA in combination with autosomal recessive disorders) and clinical restrictions (in particular the reproductive age of the mother). The current ongoing pregnancy rate and implantation rate per transfer are acceptable (27.2% and 20.8% respectively). The results may be improved by selecting younger patients and by optimizing hormonal stimulation protocols and/or embryo culture systems.SCOPUS: re.jinfo:eu-repo/semantics/publishe

Analysis of parental contribution for aneuploidy detection (APCAD): a novel method to detect aneuploidy and mosaicism in preimplantation embryos

Research question: Can (mosaic) aneuploidy be reliably detected in preimplantation embryos after multiple displacement amplification and single nucleotide polymorphism detection, independent of haplotyping and copy number detection, with a new method 'analysis of parental contribution for aneuploidy detection' or 'APCAD'? Design: This method is based on the maternal contribution, a parameter that reflects the proportion of DNA that is of maternal origin for a given chromosome or chromosome segment. A maternal contribution deviating from 50% for autosomes is strongly indicative of a (mosaic) chromosomal anomaly. The method was optimized using cell mixtures with varying ratios of euploid and aneuploid (47,XY,+21) lymphocytes. Next, the maternal contribution was retrospectively measured for all chromosomes from 349 Karyomapping samples. Results: Retrospective analysis showed a skewed maternal contribution (63.6%) in 57 out of 59 autosome meiotic trisomies and all autosome monosomies (n = 57), with values close to theoretical expectation. Thirty-two out of 7436 chromosomes, for which no anomalies had been observed with Karyomapping, showed a similarly skewed maternal contribution. Conclusions: APCAD was used to measure the maternal contribution, which is an intuitive parameter independent of copy number detection. This method is useful for detecting copy number neutral anomalies and can confirm diagnosis of (mosaic) aneuploidy detected based on copy number. Mosaic and complete aneuploidy can be distinguished and the parent of origin for (mosaic) chromosome anomalies can be determined. Because of these benefits, the APCAD method has the potential to improve aneuploidy detection carried out by comprehensive preimplantation genetic testing methods.SCOPUS: ar.jinfo:eu-repo/semantics/publishe