Detailed investigation of factors influencing amplification efficiency and allele drop-out in single cell PCR: implications for preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) of single gene disorders relies on PCR-based tests performed on single cells (polar bodies or blastomeres). Despite the use of increasingly robust protocols, allele drop-out (ADO; the failure to amplify one of the two alleles in a heterozygous cell) remains a significant problem for diagnosis using single cell PCR. In extreme cases ADO can affect >40% of amplifications and has already caused several PGD misdiagnoses. We suggest that an improved understanding of the origins of ADO will allow development of more reliable PCR assays. In this study we carefully varied reaction conditions in >3000 single cell amplifications, allowing factors influencing ADO rates to be identified. ADO was found to be affected by amplicon size, amount of DNA degradation, freezing and thawing, the PCR programme, and the number of cells simultaneously amplified. Factors found to have little or no affect on ADO were local DNA sequence, denaturing temperature (94 or 96 degrees C) and cell type. Consideration of the causal factors identified during this study should permit the design of PGD protocols that experience little ADO, thus improving the accuracy of PGD for single gene disorders.     

Development and clinical application of a strategy for preimplantation genetic diagnosis of single gene disorders combined with HLA matching

Preimplantation HLA matching has recently emerged as a tool for couples desiring to conceive a potential donor progeny for transplantation in a sibling with a life-threatening disorder. In this paper we describe a strategy optimized for preimplantation genetic diagnosis (PGD) of haemoglobinopathies combined with HLA matching. This procedure involves a minisequencing-based genotyping of HLA regions A, B, C and DRB combined with mutation analysis of the gene regions involved by mutation. Analysis of at least eight polymorphic short tandem repeat (STR) markers scattered through the HLA complex has also been included to detect potential contamination and crossing-over occurrences between HLA genes. The above assay can also be used for preimplantation HLA matching as a primary indication. The strategy was clinically applied for HLA matching in 17 cycles (14 for beta-thalassaemia, one for Wiscott-Aldrich syndrome and two for leukaemia). A reliable HLA genotype was achieved in 255/266 (95.9%) of the blastomeres. In total, 22 (14.8%) embryos were obtained that were HLA-matched with the affected siblings, 14 (9.4%) of which were unaffected and transferred back to the patients. Four clinical pregnancies were obtained, three of which (one twin, two singletons) are ongoing and were confirmed as healthy and HLA-identical with the affected children. Minisequencing-based HLA typing combined with HLA STR haplotyping has been shown to be a reliable strategy for preimplantation HLA matching. The major advantage of this approach is that the validation of a single assay can be done once and then used for the majority of the patients, reducing notably time needed for preclinical set-up of each case.     

Successful application of preimplantation genetic diagnosis for beta-thalassaemia and sickle cell anaemia in Italy

BACKGROUND: In Italy, the autosomal recessive diseases beta-thalassaemia and sickle cell anaemia are so widespread that in some regions they can be defined as 'social diseases'. In this study, nine clinical applications of preimplantation genetic diagnosis (PGD) were performed for beta-thalassaemia and sickle cell anaemia on seven Sicilian couples and carriers of beta-globin gene mutations. METHODS AND RESULTS: The studied mutations were: Cd39, HbS, IVS1 nt1, IVS1 nt6 and IVS1 nt110. ICSI was performed with partner's sperm on 131 out of 147 retrieved oocytes, and this resulted in 72 zygotes; 32 embryos were successfully biopsied on day 3. The biopsied blastomeres were lysed and the beta-globin alleles amplified by nested PCR. The mutation diagnosis was performed by restriction enzyme digestion and reverse dot-blot. The amplification efficacy was 97.2%. The genotype study of non-transferred and surplus embryos showed that the allele drop-out rate was 8.6%. Seventeen embryos were transferred in utero on day 4. All couples received an embryo transfer; of the four pregnancies obtained, three resulted in live births and one miscarried at 11 weeks. Prenatal diagnosis at the 11th week and miscarriage material analysis confirmed the PGD results. CONCLUSIONS: These studies represent the first successful application of PGD for beta-thalassaemia and sickle cell anaemia in Italy.     

Isothermal whole genome amplification from single and small numbers of cells: a new era for preimplantation genetic diagnosis of inherited disease

Preimplantation genetic diagnosis (PGD) of single gene defects following assisted conception typically involves removal of single cells from preimplantation embryos and analysis using highly sensitive PCR amplification methods taking stringent precautions to prevent contamination from foreign or previously amplified DNA. Recently, whole genome amplification has been achieved from small quantities of genomic DNA by isothermal amplification with bacteriophage 29 DNA polymerase- and exonuclease-resistant random hexamer primers. Here we report that isothermal whole genome amplification from single and small numbers of lymphocytes and blastomeres isolated from cleavage stage embryos yielded microgram quantities of amplified DNA, and allowed analysis of 20 different loci, including the DeltaF508 deletion causing cystic fibrosis and polymorphic repeat sequences used in DNA fingerprinting. As with analysis by PCR-based methods, some preferential amplification or allele drop-out at heterozygous loci was detected with single cells. With 2-5 cells, amplification was more consistent and with 10 or 20 cells results were indistinguishable from genomic DNA. The use of isothermal whole genome amplification as a universal first step marks a new era for PGD since, unlike previous PCR-based methods, sufficient DNA is amplified for diagnosis of any known single gene defect by standard methods and conditions.     

ESHRE PGD Consortium 'Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)'

Among the many educational materials produced by the European Society of Human Reproduction and Embryology (ESHRE) are guidelines. ESHRE guidelines may be developed for many reasons but their intent is always to promote best quality practices in reproductive medicine. In an era in which preimplantation genetic diagnosis (PGD) has become a reality, we must strive to maintain its efficacy and credibility by offering the safest and most effective treatment available. The dominant motivators for the development of current comprehensive guidelines for best PGD practice were (i) the absence of guidelines and/or regulation for PGD in many countries and (ii) the observation that no consensus exists on many of the clinical and technical aspects of PGD. As a consequence, the ESHRE PGD Consortium undertook to draw up guidelines aimed at giving information, support and guidance to potential, fledgling and established PGD centres. The success of a PGD treatment cycle is the result of great attention to detail. We have strived to provide a similar level of detail in this document and hope that it will assist staff in achieving the best clinical outcome for their patients.     

Diagnosing and preventing inherited disease: Multiplex polymerase chain reaction for sex determination of single mouse blastomeres

Using a multiplex nested polymerase chain reaction (PCR) methodwith single copy genes and a dinucleotide repeat locus for themouse Y and X chromosomes respectively, it was possible to discriminatebetween single cells derived from male and female embryos. Usingsingle cells, amplification of Sry and Zfy sequences was notevident in all cases. It could be calculated that, with thePCR method used, 0.04% [95% (confidence interval 0.00–2.03)]of the male embryos would erroneously be diagnosed as femaleif analysis is performed on two cells. The calculated chancefor total amplification failure, if two cells are used for analysis,would be 1.4% [95% (confidence interval 0.04–8.04)]. Themouse embryo model proved to be a helpful tool to develop skillsin the application of PCR for preimplantation genetic diagnosisat the single cell level.     

Extending preimplantation genetic diagnosis: the ethical debate. Ethical issues in new uses of preimplantation genetic diagnosis

The use of preimplantation genetic diagnosis (PGD) to screen embryos for aneuploidy and genetic disease is growing. New uses of PGD have been reported in the past year for screening embryos for susceptibility to cancer, for late-onset diseases, for HLA-matching for existing children, and for gender. These extensions have raised questions about their ethical acceptability and the adequacy of regulatory structures to review new uses. This article describes current and likely future uses of PGD, and then analyses the ethical issues posed by new uses of PGD to screen embryos for susceptibility and late-onset conditions, for HLA-matching for tissue donation to an existing child, and for gender selection. It also addresses ethical issues that would arise in more speculative scenarios of selecting embryos for hearing ability or sexual orientation. The article concludes that except for sex selection of the first child, most current extensions of PGD are ethically acceptable, and provides a framework for evaluating future extensions for nonmedical purposes that are still speculative.     

Attitudes of German infertile couples towards preimplantation genetic diagnosis for different uses: a comparison to international studies

BACKGROUND: In Germany, preimplantation genetic diagnosis (PGD) is currently not legal, but there is still a controversial debate about legalization. Studies about the attitudes of infertile couples towards PGD are rare. METHODS: A survey was conducted with 265 German infertile couples about knowledge, attitudes and prospective use of PGD. The influence of independent variables associated with approval of PGD is analysed by binary logistic regression. RESULTS: Sixty percent of respondents have heard about PGD. Eighty-seven percent support a general legalization of PGD in Germany for severe, early-onset genetic diseases. Seventy-four percent consider PGD morally acceptable. Sixty percent supported legalizing PGD for HLA-matching. But only a minority approved PGD to test for non-health-related traits. Respondents with a higher education level were the least supportive to all uses of PGD. CONCLUSIONS: Our results suggest that German infertile couples are as liberal towards PGD for health-related uses as in other western countries. They would legalize and use PGD to raise the rates to get pregnant and to avoid severe diseases of the offspring. Taking the opinions of German infertile couples into consideration could help redefine and reframe the public debate towards legalization of PGD and the moral status of the embryo in Germany.     

Strategies and clinical outcome of 250 cycles of Preimplantation Genetic Diagnosis for single gene disorders

BACKGROUND: We report on our experience with preimplantation genetic diagnosis (PGD) for single gene disorders (SGDs), from 1999 to 2004, describing strategies and overall clinical outcome of 250 cycles in 174 couples for 23 different genetic conditions. METHODS: PGD cycles included 15 for autosomal dominant, 148 for autosomal recessive and 19 for X-linked SGDs. In addition, 68 cycles of PGD for SGDs were performed in combination with HLA matching. The strategy in each case used an initial multiplex PCR, followed by minisequencing to identify the mutation(s) combined with multiplex PCR for closely linked informative markers to increase accuracy. Linkage analysis, using intragenic and/or extragenic polymorphic microsatellite markers, was performed in cases where the disease-causing mutation(s) was unknown or undetectable. RESULTS: In 250 PGD cycles, a total of 1961 cleavage stage embryos were biopsied. PCR was successful in 3409 out of 3149 (92.4%) biopsied blastomeres and a diagnosis was possible in 1849 (94.3%) embryos. Four hundred and twenty-seven embryos were transferred in 211 cycles, resulting in 71 pregnancies (33.6% per embryo transfer), including 15 biochemical pregnancies, six spontaneous miscarriages, two ectopic pregnancies, which were terminated, and nine pregnancies which are still ongoing. The remaining pregnancies were confirmed to be unaffected and went to term without complications, resulting in the birth of 35 healthy babies. CONCLUSIONS: Minisequencing for mutation detection combined with multiplex fluorescence PCR for linkage analysis is an efficient, accurate and widely applicable strategy for PGD of SGDs. Our experience provides a further demonstration that PGD is an effective clinical tool and a useful option for many couples with a high risk of transmitting a genetic disease.     

Single embryo transfer in preimplantation genetic diagnosis cycles for women <36 years does not reduce delivery rate

BACKGROUND: The Belgian legislation imposes single embryo transfer (SET) on women of <36 years in their first treatment cycle to avoid multiple pregnancies. The aim of this study is to assess the impact of this legislation on the outcome of preimplantation genetic diagnosis (PGD) for inherited diseases in young women undergoing SET. METHODS: A retrospective analysis of PGD cycles for monogenic disorders and translocations in women <36 years on their first treatment cycle. Two groups of patients were defined according to the implementation of the Belgian legislation: (i) double embryo transfer (DET), January 2001-June 2003 (ii) SET, July 2003-June 2005. The primary and secondary outcome measures were delivery per embryo transfer and multiple pregnancy rates, respectively. A subgroup analysis for monogenic disorders and translocations was performed. RESULTS: 62 cycles were included in the DET group and 73 cycles in the SET group. The mean age, number of cumulus-oocyte complexes, number of fertilized oocytes, number of biopsied and cryopreserved embryos were comparable between both groups. There was no significant difference in the delivery rates between the DET and the SET groups (33.9% versus 27.4%, respectively). Multiple pregnancies were avoided when SET was performed. When monogenic disorders and chromosomal translocations were separately evaluated, no significant difference in the delivery rate after SET was observed. CONCLUSIONS: The implementation of a SET policy in young women undergoing PGD for monogenic disorders and translocations enables a significant reduction of multiple pregnancies without significantly affecting the delivery rate.     

Diagnosis and preventing inherited disease: Allelic drop-out and preferential amplification in single cells and human blastomeres: implications for preimplantation diagnosis of sex and cystic fibrosis

Previously the diagnosis of sex and cystic fibrosis status hasbeen studied on single cells using the polymerase chain reaction(PCR). It has been suggested that allelic drop-out (PCR failureof one allele) and/or preferential amplification (hypo-amplificationof one allele) may contribute to poor reliability and misdiagnosis,although this remains controversial as some reports suggestthat allelic drop-out does not occur. We investigated an improvedmethod of diagnosing sex and cystic fibrosis in single cellsusing a new technology (fluorescent PCR) to determine the baselevel of PCR artefacts (allelic drop-out and preferential amplification)which, in combination with improved sensitivity, should improvePCR reliability and accuracy. Fluorescent PCR gives high reliability(97%) and accuracy rates (97%) in somatic cells for both sexand cystic fibrosis diagnosis and its lower detection thresholdallows allelic drop-out and preferential amplification to beeasily distinguished. We also achieved high reliability andaccuracy in diagnosing cystic fibrosis in human blastomeres.This study confirms earlier reports of both allelic drop-outand preferential amplification in single cell analysis. We demonstratethat both allelic drop-out and preferential amplification occurin somatic cells and suggest these are separate phenomena. Preferentialamplification appeared common in single cell PCR while allelicdropout apparently occurred at random in each allele. Preferentialamplification was mainly amplification of the larger allele.We suggest that some inaccuracy/misdiagnosis may be due to bothpreferential amplification as well as allelic drop-out. Otherfindings were variability in drop-out between PCR and that amplificationof signals from human blastomeres may be linked to embryo quality.We suggest that allelic drop-out is dependent on the numberof cells within the sample.     

The role of preimplantation genetic diagnosis in the management of severe rhesus alloimmunization: first unaffected pregnancy: case report

Rhesus (Rh) D alloimmunization may cause haemolytic disease of the fetus and newborn if the fetal Rh blood type is positive. Although the incidence of severe RhD alloimmunization has decreased with prophylactic anti-D immunoglobulin administration during and after pregnancy, sensitization still occurs in a small group of women. In such women, Rh disease will continue to be significant problem and for their babies who may be affected. Preimplantation genetic diagnosis (PGD) may be utilized to avoid materno-fetal blood group incompatibility in an RhD-sensitized woman. Biopsy of a single cell from early cleavage-stage embryos screening for RhD-negative embryos allows the transfer of only RhD-negative embryo(s) into the uterus. This avoids any complications related to haemolytic disease of the fetus and newborn. This article describes the first reported case of an unaffected pregnancy using PGD for Rh disease. IVF and embryo transfer resulted in a clinical pregnancy and the birth of a healthy girl confirmed to be blood type RhD negative. PGD in couples with a heterozygous RhD-positive male partner provides an option for avoiding haemolytic disease of the newborn in RhD alloimmunized mothers.     

New advances in human embryology: implications of the preimplantation diagnosis of genetic disease

The diagnosis of genetic disease in preimplantation embryosis discussed. The typing of spermatozoa may be feasible forfactors such as the presence of an X and Y chromosome. Embryosmight be typed by non-invasive methods, by assessing their uptakeof metabolites although the widest opportunities may arise bythe use of invasive methods which involve the removal of oneor a small number of cells. The methods of diagnosis are discussed,including enzyme assays and the use of DNA probes, preliminaryresults with human embryos are presented and the difficultiesrelated to these techniques are debated. The low rate of implantationof replaced embryos will mean that many embryos will have tobe diagnosed, and certain embryological factors such as thehigh incidence of chromosomal imbalance and the problems of‘imprinting’ might obscure certain diagnoses. Theadvantages and disadvantages of the method are discussed.     

Improving clinical preimplantation genetic diagnosis for cystic fibrosis by duplex PCR using two polymorphic markers or one polymorphic marker in combination with the detection of the DeltaF508 mutation

Cystic fibrosis (CF) is an autosomal recessive disease characterized by obstruction and chronic infection of the respiratory tract and pancreatic insufficiency. The first preimplantation genetic diagnosis (PGD) for CF was carried out in 1992. At our centre the first cycle was performed in 1993. However, the number of known CF mutations is >1000, so developing mutation-specific PCR protocols for PGD is unfeasible. This is why a number of marker-based duplex PCRs were developed at the single cell level. A duplex PCR of a mutation and one or two microsatellites is not only a diagnostic tool, but it can also be used as a control for allele drop-out and contamination. During PGD, embryos obtained in vitro are analysed for the presence or absence of a particular genetic disease, after which only embryos shown to be free of this disease are returned to the mother. In total, 22 PGD cycles with duplex PCR (IVS8CA/IVS17BTA, DeltaF508/IVS8CA, DeltaF508/IVS17BTA and D7S486/D7S490) were carried out in 16 couples, which resulted in four ongoing pregnancies and one miscarriage.     

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.     

Real-time PCR for single-cell genotyping in sickle cell and thalassemia syndromes as a rapid, accurate, reliable, and widely applicable protocol for preimplantation genetic diagnosis

Sickle-cell and beta-thalassemia syndromes are priority genetic diseases for prevention programs involving population screening with the option of prenatal diagnosis for carrier couples. Preimplantation genetic diagnosis (PGD) represents a specialized alternative to prenatal diagnosis and is most appropriately used for couples with an unsuccessful reproductive history and/or undergoing assisted reproduction. However, clinical application of PGD has been hindered by difficulties in reliably transferring molecular diagnostic protocols to the single-cell level. We standardized and validated a protocol involving first-round multiplex PCR, amplifying the region of the beta-globin gene containing most of the common disease mutations world-wide and two unlinked microsatellite markers (GABRB3 and D13S314), followed by: 1) analysis of beta-globin genotypes with real-time PCR and 2) microsatellite sizing to exclude chance contamination. The protocol was standardized on 100 single lymphocytes from a beta-thalassemia heterozygote, including 15 artificially contaminated samples, the latter demonstrated through microsatellite analysis. PCR failure and allele drop-out (ADO) were observed in one (uncontaminated) sample each (1.2%). A pilot study in six clinical PGD cycles with five different beta-globin genotype interactions achieved results (in 5-6 hr) in 46 out of 50 single blastomeres (92%), all concordant with results from an established PGD method applied simultaneously; microsatellite analysis detected only parental alleles, excluding contamination. Beta-globin genotypes were also confirmed in two blastomeres through prenatal diagnosis (twin pregnancy), and in 11 out of 12 spare embryos, revealing one incident of ADO. Overall, the protocol proved to be sensitive, accurate, reliable, rapid, and applicable for many genotype interactions, with internal monitoring of contamination, thus fulfilling all requirements for clinical PGD application.     

Parental mosaicism is a pitfall in preimplantation genetic diagnosis of dominant disorders

PCR amplification on single cells is prone to allele drop-out (PCR failure of one allele), a cause of misdiagnosis in preimplantation genetic diagnosis (PGD). Owing to this error risk, PGD usually relies on both direct and indirect genetic analyses. When the affected partner is the sporadic case of a dominant disorder, building haplotypes require spermatozoon or polar body testing prior to PGD, but these procedures are cost and time-consuming. A couple requested PGD because the male partner suffered from a dominant Cowden syndrome (CS). He was a sporadic case, but the couple had a first unaffected child and the non-mutated paternal haplotype was tentatively deduced. The couple had a second spontaneous pregnancy and the fetus was found to carry the at-risk haplotype but not the PTEN mutation. The mutation was present in blood from the affected father, but at low level, confirming the somatic mosaicism. Ignoring the possibility of mosaicism in the CS patient would have potentially led to selection of affected embryos. This observation emphasizes the risk of PGD in families at risk to transmit autosomal-dominant disorder when the affected partner is a sporadic case.     

Diagnostic efficiency, embryonic development and clinical outcome after the biopsy of one or two blastomeres for preimplantation genetic diagnosis

BACKGROUND: Preimplantation genetic diagnosis or screening (PGD, PGS) involves embryo biopsy on Day 3. Opting for one- or two-cell biopsy is a balance between the lowest risk for misdiagnosis on the one hand and the highest chance for a pregnancy on the other hand. METHODS: A prospective controlled trial was designed and 592 ICSI cycles were randomly assigned to the one-cell (group I) or the two-cell group (group II). Primary outcomes were diagnostic efficiency and embryonic development to delivery with live birth (analysed by cycle). The false-positive rate for the PCR cycles is presented as a secondary outcome (analysed by embryo). RESULTS: A strong significant correlation was observed between embryonic developmental stage on Day 3 and post-biopsy in vitro development on Day 5 (P < 0.0001). The influence of the intervention on Day 3 was less significant (P = 0.007): the biopsy of one cell is less invasive than the biopsy of two cells. PCR diagnostic efficiency was 88.6% in group I and 96.4% in group II (P = 0.008). For the fluorescence in situ hybridization (FISH) PGD cycles no significant difference in efficiency was obtained (98.2 and 97.5% in group I and II, respectively). Similar delivery rates with live birth per started cycle were obtained [58/287 or 20.2% in group I versus 52/303 or 17.2% in group II, P = 0.358; the absolute risk reduction = 3.05%; 95% confidence interval (CI): -3.24, 9.34]. Post-PGD PCR reanalysis showed six false positives in 97 embryos (6.2%) in group II and none in group I (91 embryos reanalysed). No false negatives were found. CONCLUSIONS: While removal of two blastomeres decreases the likelihood of blastocyst formation, compared with removal of one blastomere, Day 3 in vitro developmental stage is a stronger predictor for Day 5 developmental potential than the removal of one or two cells. The biopsy of only one cell significantly lowers the efficiency of a PCR-based diagnosis, whereas the efficiency of the FISH PGD procedure remains similar whether one or two cells are removed. Delivery rates with live birth per started cycle were not significantly different.     

First preimplantation genetic diagnosis of hereditary retinoblastoma using informative microsatellite markers

Retinoblastoma is a malignant intra-ocular tumour of developing retina initiated by inactivation of both alleles of the retinoblastoma susceptibility (RB1) gene. This paper reports the first clinical experience of preimplantation genetic diagnosis (PGD) for hereditary retinoblastoma using two highly polymorphic microsatellite markers RB1.20 and D13S284, located within and close to the RB1 gene respectively. Duplex PCRs were tested on more than 300 single lymphocytes from heterozygous individuals at both loci, in order to test the accuracy and reliability of the single-cell protocol. This procedure requires a nested PCR and the analysis of fluorescently labelled PCR products on an automatic DNA sequencer. Amplification efficiency and allele drop-out rates ranged from 96.7 to 98.4%, and 3.7 to 5.4% respectively. This test was found to be accurate and reliable enough to be applied to the study of human blastomeres. Subsequently, this approach was used in a PGD treatment cycle for a couple who already had a child affected with hereditary retinoblastoma and found to be informative for both microsatellite markers.     

Controlling misdiagnosis errors in preimplantation genetic diagnosis: a comprehensive model encompassing extrinsic and intrinsic sources of error

We have developed a mathematical model to explore accuracy of preimplantation genetic diagnosis (PGD) using single cell polymerase chain reaction (PCR). The model encompasses both extrinsic technical errors and intrinsic errors related to nuclear and chromosomal abnormalities. Using estimates for these errors, we have calculated the probability of a serious error (affected embryo diagnosed as unaffected) using a variety of strategies designed to increase the accuracy of PGD. Additional information from genotyping a linked marker or a second biopsied cell reduces the probability of replacing an affected embryo, while ensuring that sufficient unaffected embryos can be replaced. For a recessive disease, two genotypes are required to ensure a low probability of replacing an affected embryo (<1%) with a high proportion of unaffected embryos eligible for replacement (68%). These genotypes may be from a single cell with linked marker, or disease genotypes from two cells. PGD of a dominant disease is more difficult, as it relies on the amplification of a single copy of the mutation. Genotypes from two biopsied cells are required to ensure that a high proportion of unaffected embryos are eligible for replacement. This model can be used as a clinical tool to prioritize embryos for transfer in a PGD cycle.