The impact of mosaicism in preimplantation genetic diagnosis (PGD): approaches to PGD for dominant disorders in couples without family history.

OBJECTIVES: Mosaicism in certain dominant disorders may result in a 'non-Mendelian' transmission for the causative mutation. Preimplantation genetic diagnosis (PGD) is available for patients with inherited disorders to achieve an unaffected pregnancy. We present our experience for two female patients with different dominantly inherited autosomal disorders; neurofibromatosis type 1 (NF1) and tuberous sclerosis complex type 2 (TSC2). METHODS: PGD protocol development was carried out using single cells from the patients. PGD was carried out on polar bodies and different embryonic cells. RESULTS: Protocol development for NF1 using lymphocytes from the patient suggested mosaicism for the mutation. This was supported further by quantitative fluorescent-PCR performed on genomic DNA. During PGD, polar bodies and blastomeres lacked the mutation that probably was absent or present at very low levels in the patient's germline. Single lymphocyte analysis during protocol development for TSC2 did not indicate mosaicism; however, analysis of single buccal cells and multiple embryo biopsies across two consecutive IVF/PGD cycles confirmed gonosomal mosaicism. CONCLUSIONS: The trend in PGD is for blastocyst biopsy followed by whole genome amplification, eliminating single cell analysis. In the case of certain dominantly inherited disorders, pre-PGD single cell analysis is beneficial to identify potential mosaicism that ensures robust protocols. © 2016 John Wiley & Sons, Ltd.

Evaluation of PCR-based preimplantation genetic diagnosis applied to monogenic diseases: a collaborative ESHRE PGD consortium study.

Preimplantation genetic diagnosis (PGD) for monogenic disorders currently involves polymerase chain reaction (PCR)-based methods, which must be robust, sensitive and highly accurate, precluding misdiagnosis. Twelve adverse misdiagnoses reported to the ESHRE PGD-Consortium are likely an underestimate. This retrospective study, involving six PGD centres, assessed the validity of PCR-based PGD through reanalysis of untransferred embryos from monogenic-PGD cycles. Data were collected on the genotype concordance at PGD and follow-up from 940 untransferred embryos, including details on the parameters of PGD cycles: category of monogenic disease, embryo morphology, embryo biopsy and genotype assay strategy. To determine the validity of PCR-based PGD, the sensitivity (Se), specificity (Sp) and diagnostic accuracy were calculated. Stratified analyses were also conducted to assess the influence of the parameters above on the validity of PCR-based PGD. The analysis of overall data showed that 93.7% of embryos had been correctly classified at the time of PGD, with Se of 99.2% and Sp of 80.9%. The stratified analyses found that diagnostic accuracy is statistically significantly higher when PGD is performed on two cells versus one cell (P=0.001). Se was significantly higher when multiplex protocols versus singleplex protocols were applied (P=0.005), as well as for PGD applied on cells from good compared with poor morphology embryos (P=0.032). Morphology, however, did not affect diagnostic accuracy. Multiplex PCR-based methods on one cell, are as robust as those on two cells regarding false negative rate, which is the most important criteria for clinical PGD applications. Overall, this study demonstrates the validity, robustness and high diagnostic value of PCR-based PGD.

Modification of the triplet repeat primed polymerase chain reaction method for detection of the CTG repeat expansion in myotonic dystrophy type 1: application in preimplantation genetic diagnosis.

OBJECTIVE: To overcome problems associated with the use of triplet repeat primed polymerase chain reaction (TP-PCR) in preimplantation genetic diagnosis (PGD) of myotonic dystrophy type 1 (DM1). DESIGN: Clinical research study. SETTING: UCL Centre for PGD and Centre for Reproductive and Genetic Health. PATIENT(S): Seven couples undergoing PGD for DM1. INTERVENTION(S): A modified TP-PCR protocol (mTP-PCR) for the reliable detection of both expanded and nonexpanded alleles in DMPK was optimized using single lymphocytes. Four cycles of PGD were performed with TP-PCR for diagnosis and a further 10 cycles with mTP-PCR. MAIN OUTCOME MEASURE(S): Amplification efficiency, allele dropout, diagnosis rate, and delivery rate. RESULT(S): Preliminary testing showed that the TP-PCR amplification efficiency was higher using lymphocytes versus buccal cells. Single lymphocytes gave very high amplification efficiencies for both protocols (99% to 100%). There were no false-positive or false-negative results for 148 single lymphocytes tested with mTP-PCR compared with 9% (5 out of 54) false-positive results with TP-PCR, indicating the improved accuracy of the modified protocol. In embryos, the diagnosis rate was 95.6% with mTP-PCR and 75% with TP-PCR. CONCLUSION(S): For PGD of DM1, mTP-PCR is recommended. It may also be applied as a rapid screen for DMPK expansions in individuals with symptoms of DM1, relatives of known mutation carriers, or in prenatal diagnosis.

Preimplantation genetic diagnosis for myotonic dystrophy type 1 in the UK.

Myotonic dystrophy type 1 (DM1) is a dominant multisystemic disorder caused by expansion of a trinucleotide repeat in a non-coding region of DMPK. Prenatal diagnosis (PND) is available; however, the decision to terminate affected pregnancies is difficult as the extent of disability is hard to predict from the size of the expansion. In preimplantation genetic diagnosis (PGD) genetic analysis is carried out before the establishment of pregnancy. This paper reviews the largest number of cycles of PGD for DM1 in the UK indicating that PGD is a practical option for affected couples.

Preimplantation genetic diagnosis for myotonic dystrophy type 1: detection of crossover between the gene and the linked marker APOC2.

OBJECTIVE: To report two cases of preimplantation genetic diagnosis (PGD) for myotonic dystrophy type I (DM1) where cross-over between the DMPK locus and a linked polymorphic marker APOC2 was detected. METHODS: Embryos from in vitro fertilisation (IVF) were biopsied at day 3 of development and single blastomeres collected. Diagnosis was performed by duplex or triplex fluorescent-polymerase chain reaction (F-PCR) to amplify DMPK and APOC2 loci, or DMPK with APOC2 and D19S112 polymorphic markers. RESULTS: A total of 22 oocytes were retrieved from the two patients, 20 were inseminated of which 15 fertilized (75%) and were suitable for biopsy on day 3. A diagnosis was obtained for 12 embryos (80%) and was confirmed in all un-transferred embryos. Crossover between DM1 and APOC2 was detected in two embryos from the two different couples. Transfer of two embryos took place in both cases resulting in two pregnancies. Each couple have had a healthy baby. CONCLUSION: The above cases highlight the importance of using more than one linked polymorphic marker in PGD-PCR protocols and emphasize the danger of using APOC2 as the sole marker to identify the DM1 mutation.

Variations in humanized and defined culture conditions supporting derivation of new human embryonic stem cell lines.

The evolution of "humanized" (i.e., free of animal sourced reagents) and ultimately chemically defined culture systems for human embryo stem cell (hESC) isolation and culture is of importance to improving their efficacy and safety in research and therapeutic applications. This can be achieved by integration of a multitude of individual approaches to replace or eliminate specific animal sourced reagents into a single comprehensive protocol. In the present study our objective was to integrate strategies obviating reliance on some of the most poorly defined and path-critical factors associated with hESC derivation, namely the use of animal immune compliment to isolate embryo inner cell mass, and animal sourced serum products and feeder cells to sustain hESC growth and attachment. As a result we report the derivation of six new hESC lines isolated by outgrowth from whole blastocysts on an extracellular matrix substrate of purified human laminin (Ln) with transitional reliance on mitotically inactivated human fibroblast (HDF) feeder cells. With this integrated system hESC lines were isolated using either HDF conditioned medium supplemented with a bovine-sourced serum replacement (bSRM), or a defined serum-free medium (SFM) containing only human sourced and recombinant protein. Further, outgrowth of embryonic cells from whole blastocysts in both media could be achieved for up to 1 week without reliance on feeder cells. All variant conditions sustained undifferentiated cell status, a stable karyotype and the potential to form cells representative of all three germinal lineages in vitro and in vivo, when transitioned off of feeders onto Laminin or Matrigel. Our study thus demonstrates the capacity to integrate derivation strategies eliminating a requirement for animal immune compliment and serum products, with a transitional requirement for human feeder cells. This represents another sequential step in the generation of therapeutic grade stem cells with reduced risk of zoonotic pathogen transmission.

Rapid and simple prenatal diagnosis of common chromosome disorders: advantages and disadvantages of the molecular methods FISH and QF-PCR.

Molecular techniques have been developed for prenatal diagnosis of the most common chromosome disorders (trisomies 21, 13, 18 and sex chromosome aneuploidies) where results are available within a day or two. This involves fluorescence in situ hybridization (FISH) and microscopy analysis of fetal cells or quantitative fluorescence polymerase chain reaction (QF-PCR) on fetal DNA. Guidance is provided on the technological pitfalls in setting up and running these methods. Both methods are reliable, and the risk for misdiagnosis is low, although slightly higher for FISH. FISH is also more labour intensive than QF-PCR, the latter lending itself more easily to automation. These tests have been used as a preamble to full chromosome analysis by microscopy. However, there is a trend to apply the tests as 'stand-alone' tests for women who are at relatively low risk of having a baby with a chromosome disorder, in particular that associated with advanced age or results of maternal serum screening programmes. These women comprise the majority of those currently offered prenatal diagnosis with respect to fetal chromosome disorders and if introduced on a larger scale, the use of FISH and QF-PCR would lead to substantial economical savings. The implication, on the other hand, is that around one in 500 to one in 1000 cases with a mentally and/or physically disabling chromosome disorder would remain undiagnosed.