Robust Preimplantation Genetic Testing Strategy for Myotonic Dystrophy Type 1 by Bidirectional Triplet-Primed Polymerase Chain Reaction Combined With Multi-microsatellite Haplotyping Following Whole-Genome Amplification

Myotonic dystrophy type 1 (DM1) is caused by expansion of the DMPK CTG trinucleotide repeat. Disease transmission to offspring can be avoided through prenatal diagnosis or preimplantation genetic testing for monogenic disorders (PGT-M). We describe a robust strategy for DM1 PGT-M that can be applied to virtually any at-risk couple. This strategy utilizes whole-genome amplification, followed by triplet-primed PCR (TP-PCR) detection of expanded DMPK alleles, in parallel with single-tube haplotype analysis of 12 closely linked and highly polymorphic microsatellite markers. Bidirectional TP-PCR and dodecaplex marker PCR assays were optimized and validated on whole-genome amplified single lymphoblasts isolated from DM1 reference cell lines, and tested on a simulated PGT-M case comprising a parent-offspring trio and three simulated embryos. Bidirectional DMPK TP-PCR reliably detects repeat expansions even in the presence of non-CTG interruptions at either end of the expanded allele. Misdiagnoses, diagnostic ambiguity, and couple-specific assay customization are further minimized by the use of multi-marker haplotyping, preventing the loss of potentially unaffected embryos for transfer.

Single-Tube Dodecaplex PCR Panel of Polymorphic Microsatellite Markers Closely Linked to the DMPK CTG Repeat for Preimplantation Genetic Diagnosis of Myotonic Dystrophy Type 1

BACKGROUND

Preimplantation genetic diagnosis (PGD) of myotonic dystrophy type 1 (DM1) currently uses conventional PCR to detect nonexpanded dystrophia myotonica protein kinase (DMPK) alleles or triplet-primed PCR to detect the CTG-expanded alleles, coupled with analysis of linked microsatellite markers to increase diagnostic accuracy. We aimed to simplify the process of identification and selection of informative linked markers for application to DM1 PGD.

METHODS

An in silico search was performed to identify all markers within 1-1.5 Mb flanking the DMPK gene. Five previously known (D19S559, APOC2, D19S543, D19S112, and BV209569) and 7 novel (DM45050, DM45178, DM45209, DM45958, DM46513, DM46892, and DM47004.1) markers with potentially high heterozygosity values and polymorphism information content were selected and optimized in a single-tube multiplex PCR panel.

RESULTS

Analysis of 184 DNA samples of Chinese and Caucasian individuals (91 from unrelated, anonymized cord blood of Chinese babies born at the National University Hospital, Singapore, and 93 Caucasian DNA samples from the Human Variation Panel HD100CAU) confirmed the high polymorphism indices of all markers (polymorphism information content >0.5), with observed heterozygosity values ranging from 0.62-0.93. All individuals were heterozygous for at least 6 markers, with 99.5% of individuals heterozygous for at least 2 markers on either side of the DMPK CTG repeat. The dodecaplex marker assay was successfully validated on 42 single cells and 12 whole genome amplified single cells.

CONCLUSIONS

The DM1 multiplex PCR panel is suitable for use in DM1 PGD either as a standalone linkage-based assay or as a complement to DMPK CTG repeat expansion-mutation detection.

Application of a reliable and rapid polymerase chain reaction based method in the diagnosis of myotonic dystrophy type 1 (DM1) in India

DM1 is caused by CTG repeat expansion in the 3′-UTR of the DMPK gene. DM1 patients have expansions of greater than 50 repeats and up to many thousands. The intention of the present study is the establishment of reliable and rapid polymerase chain reaction methodology in early screening of DM1 patients and their family members. PCR followed by TP-PCR was assessed for screening of 27 cases (from 26 families) and 75 family members and 300 control samples. All patients had CTG repeat expansion while forty seven (63%) and twenty eight (37%), out of seventy five family members were heterozygous and homozygous respectively. Similarly, two hundred thirty (76.77%) and seventy (23.33%), out of three hundred control subjects were heterozygous and homozygous respectively and the number of repeats varied from 5 to 35. Thirteen complete family screenings were done. Thus, TP-PCR is a reliable and rapid molecular technique for the detection of CTG repeat expansion in DM1.

Molecular genetics and genetic testing in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common adult onset muscular dystrophy, presenting as a multisystemic disorder with extremely variable clinical manifestation, from asymptomatic adults to severely affected neonates. A striking anticipation and parental-gender effect upon transmission are distinguishing genetic features in DM1 pedigrees. It is an autosomal dominant hereditary disease associated with an unstable expansion of CTG repeats in the 3'-UTR of the DMPK gene, with the number of repeats ranging from 50 to several thousand. The number of CTG repeats broadly correlates with both the age-at-onset and overall severity of the disease. Expanded DM1 alleles are characterized by a remarkable expansion-biased and gender-specific germline instability, and tissue-specific, expansion-biased, age-dependent, and individual-specific somatic instability. Mutational dynamics in male and female germline account for observed anticipation and parental-gender effect in DM1 pedigrees, while mutational dynamics in somatic tissues contribute toward the tissue-specificity and progressive nature of the disease. Genetic test is routinely used in diagnostic procedure for DM1 for symptomatic, asymptomatic, and prenatal testing, accompanied with appropriate genetic counseling and, as recommended, without predictive information about the disease course. We review molecular genetics of DM1 with focus on those issues important for genetic testing and counseling.

The expanding world of myotonic dystrophies: how can they be detected?

Myotonic dystrophy (DM) comprises at least two genetically distinct forms, both of which are caused by expansions of microsatellite repeats. The expansion of a CTG repeat in the DMPK gene leads to the first genetic form (DM type 1), and the expansion of a CCTG repeat in the ZNF9 gene causes the second genetic form of the disease (DM type 2). In both cases, the repeat units may expand to several thousand repeats, and the number of repeats in the expanded alleles shows a high degree of meiotic and somatic instability. The unprecedented size of expansions and their dynamic nature still represents a diagnostic challenge, which has been facilitated using different methods and modifications since the identification of the underlying mutations of these disorders. Here, we present an overview of the basic methods described for the purpose of identification of the DM type 1 and DM type 2 expansions and discuss particular modifications and improvements implemented to extend the detection ranges of these methods. Our review focuses on the advantages and disadvantages of the methods based on Southern blot analysis, polymerase chain reaction amplification, and in situ hybridization techniques and also on the possibilities of preimplantation and prenatal genetic testing.

The reproductive outcome of female patients with myotonic dystrophy type 1 (DM1) undergoing PGD is not affected by the size of the expanded CTG repeat tract

PURPOSE

This study aims to analyze the relationship between trinucleotide repeat length and reproductive outcome in a large cohort of DM1 patients undergoing ICSI and PGD.

METHODS

Prospective cohort study. The effect of trinucleotide repeat length on reproductive outcome per patient was analyzed using bivariate analysis (T-test) and multivariate analysis using Kaplan-Meier and Cox regression analysis.

RESULTS

Between 1995 and 2005, 205 cycles of ICSI and PGD were carried out for DM1 in 78 couples. The number of trinucleotide repeats does not have an influence on reproductive outcome when adjusted for age, BMI, basal FSH values, parity, infertility status and male or female affected. Cox regression analysis indicates that cumulative live birth rate is not influenced by the number of trinucleotide repeats. The only factor with a significant effect is age (p < 0.05).

CONCLUSION

There is no evidence of an effect of trinucleotide repeat length on reproductive outcome in patients undergoing ICSI and PGD.

Current status of the approach to assisted reproduction

Assisted reproductive technologies are important tools in the clinical armamentarium used to treat both female and male infertility disorders. Pre-implantation genetic diagnosis offers couples at risk of having children with inheritable disorders the ability to analyze the genetic make-up of embryos before transfer. For patients undergoing treatment of cancer with chemotherapy or radiation therapy, these technologies offer the potential for the preservation of future fertility. As technology evolves, it is likely the clinical applications of assisted reproduction will continue to develop and expand in the future to enhance fertility.

Preimplantation genetic diagnosis for myotonic dystrophy type 1: upon request to child

Preimplantation genetic diagnosis (PGD) is an alternative to prenatal diagnosis for patients at risk of transmitting an inherited disease such as myotonic dystrophy type 1(DM1) to their offspring. In this paper, the clinical application of preimplantation diagnosis for DM1 upon request to children born is described in a large cohort of risk couples. PGD could be offered to all 78 couples opting for PGD regardless of the triplet repeat size. The incidence of major complications was minimalised following a careful assessment in affected DM1 females anticipating possible cardiological, obstetrical and anaesthetical problems. A live-birth delivery rate per cycle with oocyte retrieval of 20% was the outcome. Forty-eight of the 49 children born are in good health and have normal psychomotor development.

Successful hematopoietic stem cell transplantation for Fanconi anemia from an unaffected HLA-genotype–identical sibling selected using preimplantation genetic diagnosis

The only proven cure for Fanconi anemia (FA)-associated bone marrow failure is successful allogeneic hematopoietic stem cell transplantation (HSCT). However, HSCT with donors other than HLA-identical siblings is associated with high morbidity and poor survival. Therefore, we used preimplantation genetic diagnosis (PGD) to select an embryo produced by in vitro fertilization (IVF) that was unaffected by FA and was HLA-identical to the proband. The patient was a 6-year-old girl with FA and myelodysplasia previously treated with oxymetholone and prednisone. After her parents underwent 5 cycles of IVF with intrauterine transfer of 7 embryos over a span of 4 years, successful pregnancy ensued. Twenty-eight days after delivery, the patient underwent transplantation with her newborn sibling donor's HLA-identical umbilical cord blood hematopoietic stem cells (HSCs). Neutrophil recovery occurred on day 17 without subsequent acute or chronic graft-versus-host disease. Currently, 2.5 years after transplantation, the patient is well and hematopoiesis is normal. In summary, we have described the first successful transplantation, using IVF and PGD, of HSCs from a donor selected on the basis of specific, desirable disease and HLA characteristics. The medical, legal, and ethical issues involved with this approach are discussed. (Blood. 2004;103:1147-1151)

Comparison between fluorescence in situ hybridization (FISH) and quantitative-fluorescent polymerase chain reaction (QF-PCR) for the detection of aneuploidies in single blastomeres

OBJECTIVES

The aim of our investigation was to compare the efficiencies of the fluorescence in situ hybridization (FISH) and the quantitative-fluorescent PCR (QF-PCR) methods for the detection of sexing and numerical chromosome disorders in single blastomeres collected from the same preimplantation human embryos.

METHODS

FISH analysis was carried out on 145 blastomeres from the 79 surplus embryos with probes specific for chromosomes 13, 18, 21, X, and Y. QF-PCR was performed with each one or two of the primers specific for the same chromosomes on 151 blastomeres from the same embryos obtained from patients undergoing IVF treatment.

RESULTS

Analyses were possible on 135 blastomeres (93%) by FISH and on 117 blastomeres (77%) by QF-PCR. Of 65 embryos, which could be analyzed by both methods, 20 embryos (31%) were diagnosed as abnormal.

CONCLUSION

The present study shows that FISH tests are more accurate than QF-PCR assays for the detection of numerical chromosome disorders when performed on single blastomeres.

Preimplantation diagnosis for ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is a severe X-linked metabolic disorder leading to hyperammonaemia and death shortly after birth. Prenatal diagnosis for OTC deficiency is available, but may require termination of pregnancy if affected. Thus there is a need for an option for pre-pregnancy testing, to pre-select OTC deficiency-free embryos for transfer, thus avoiding prenatal diagnosis and pregnancy termination. Preimplantation genetic diagnosis (PGD) for OTC deficiency has been developed, using sequential first and second polar body analysis; it was applied in a woman carrying the R26Q mutation in the exon 1 of OTC gene. The first and second polar bodies were removed following maturation and fertilization of oocytes in a standard IVF protocol, and analysed using a multiplex nested PCR. R26Q mutation was tested simultaneously with linked markers in six zygotes, resulting in detection of the embryos with a mutation-free maternal contribution; these were transferred back to the patient, yielding pregnancy and birth of a healthy child. This is the first PGD for OTC deficiency resulting in the birth of an unaffected child.

Preimplantation diagnosis for p53 tumour suppressor gene mutations

Preimplantation genetic diagnosis (PGD) was introduced for high-risk couples to avoid establishing affected pregnancies potentially requiring termination following prenatal diagnosis. This opens the possibility for PGD for late onset disorders with genetic predisposition, including inherited cancer predisposition, because only embryos free from the predisposing gene may be transferred back to the patient, with no potential risk for pregnancy termination. PGD was performed for two couples, one with maternally and one with paternally derived p53 tumour-suppressor mutations, 902insC in exon 8 and G524A in exon 5, respectively. This involved a standard IVF protocol, allowing oocytes or embryos to be tested prior to their transfer back to uterus. Maternal mutation was tested by sequential PCR analysis of the first and second polar bodies, removed following maturation and fertilization of oocytes, while paternal mutation analysis required embryo biopsy at the cleavage stage. To avoid misdiagnosis due to allele drop out, multiplex nested PCR was applied, involving p53 mutation analysis simultaneously with the linked short tandem repeats in intron 1. Of 10 oocytes tested in two PGD cycles for 902insC mutation, four unaffected oocytes were pre-selected for transfer yielding no clinical pregnancy. Of 18 embryos analysed in two cycles for G524A mutation, seven mutation-free embryos were detected, two of which were transferred in each cycle, resulting in a singleton pregnancy and birth of a mutation-free child. This is the first PGD for inherited cancer predisposition determined by p53 tumour suppressor mutations, resulting in a clinical pregnancy and birth of a child free from inherited cancer predisposition.

Current status of preimplantation diagnosis for single gene disorders

Preimplantation genetic diagnosis (PGD) has become an established procedure for avoiding the birth of affected children with single gene disorders. PGD is performed through polar body or blastomere biopsy, which has no deleterious effect on pre- and post-implantation development. This review describes the most recent developments and current changes in the spectrum of conditions for which PGD has been applied. The most recent applications of PGD include congenital malformations, blood group incompatibility and an increasing number of late onset disorders with genetic predisposition, all of which have not previously been diagnosed using PGD. Despite ethical concerns, PGD has also been used for preselection of unaffected and HLA matched embryos, and recently for preimplantation HLA matching without testing for the causative gene. This extends the practical value of PGD, with its utility being no longer limited to prevention of single gene disorders, by expanding it to treatment of siblings requiring stem cell transplantation.

Issues and concerns of couples presenting for preimplantation genetic diagnosis (PGD)

BACKGROUND

The use of preimplantation genetic diagnosis (PGD) to select genetically 'normal' human embryos and to transfer them to the uterus of a woman has generated considerable controversy. Debate has occurred over the implications of PGD, sex selection, safety of embryonic manipulation and eugenics. This study evaluates a range of social and moral concerns of couples towards PGD and assisted reproductive technologies (ART) prior to treatment to obtain unbiased authentic attitudes independent of the treatment cycle and the outcome.

METHODS

A total of 121 subjects were administered a structured questionnaire after each couple's in vitro fertilization (IVF) or genetic counselling session. Group A consisted of 41 subjects presenting for PGD of single gene disorders (PGD-SG) and group B consisted of 48 subjects undertaking PGD for aneuploidy screening (PGD-AS). A control group consisted of 32 subjects that were about to commence their first IVF cycle.

RESULTS AND DISCUSSION

All groups found PGD to be a highly acceptable treatment. They expressed little concern about its extension to testing non-disease states such as sex and they were strongly in favour of a shared decision-making model in which couples have considerable autonomy over decisions about the embryo(s) to transfer. Differences between the groups included issues surrounding the transfer of embryos, restrictions to PGD and the destruction of embryos.

The genetic revolution: new ethical issues for obstetrics and gynaecology

The genomic revolution inherently changes the paradigms that have informed the interactions between patient and physician. These changes obligate physicians both to continually learn about the advances occurring in genetic testing and to review their interactions in light of the changing ethical issues these advances uncover. Particular areas for concern are the use of genetic testing for predisposition genes. The issues differ between uses for adults, for children and for pre-implantation genetics. Furthermore, there are issues of justice raised by limited access to these technologies, research confidentiality, potential discrimination and the meaning of individuality in an era of potential genetic cloning. These changes require obstetrician/gynaecologists to advocate for the best interests of both their patients and those who may not be able to voice their interests, for example children-to-be and research subjects in developing countries.

Preimplantation genetic diagnosis for single gene disorders: experience with five single gene disorders

We report our experience of 14 preimplantation genetic diagnosis (PGD) cycles in eight couples carrying five different single gene disorders, during the last 18 months. Diagnoses were performed for myotonic dystrophy (DM), cystic fibrosis (CF) [Delta F508 and exon 4 (621+1 G>T)], fragile X and CF simultaneously, and two disorders for which PGD had not been previously attempted, namely neurofibromatosis type 2 (NF2) and Crouzon syndrome. Diagnoses for single gene disorders were carried out on ideally two blastomeres biopsied from Day 3 embryos. A highly polymorphic marker was included in each diagnosis to control against contamination. For the dominant disorders, where possible, linked polymorphisms provided an additional means of determining the genotype of the embryo hence reducing the risk of misdiagnosis due to allele dropout (ADO). Multiplex fluorescent polymerase chain reaction (F-PCR) was used in all cases, followed by fragment analysis and/or single-stranded conformation polymorphism (SSCP) for genotyping. Embryo transfer was performed in 13 cycles resulting in one biochemical pregnancy for CF, three normal deliveries (a twin and a singleton) and one early miscarriage for DM and a singleton for Crouzon syndrome. In each case the untransferred embryos were used to confirm the diagnoses performed on the biopsied cells. The results were concordant in all cases. The inclusion of a polymorphic marker allowed the detection of extraneous DNA contamination in two cells from one case. Knowing the genotype of the contaminating DNA allowed its origin to be traced. All five pregnancies were obtained from embryos in which two blastomeres were biopsied for the diagnosis. Our data demonstrate the successful strategy of using multiplex PCR to simultaneously amplify the mutation site and a polymorphic locus, fluorescent PCR technology to achieve greater sensitivity, and two-cell biopsy to increase the efficiency and success of diagnoses.

Preimplantation testing for phenylketonuria

OBJECTIVE

To use preimplantation genetic diagnosis to achieve a phenylketonuria-free pregnancy in a couple at 50% risk for producing an affected child.

DESIGN

DNA analysis of the first and second polar bodies (PB1 and PB2) obtained from oocytes of a heterozygous mother in IVF-ET, with the goal of identifying and transferring back to the patient the embryos resulting from mutation-free oocytes.

SETTING

IVF program of Reproductive Genetics Institute, Chicago, Illinois.

PATIENT(S)

A mother carrying the R408W mutation and a father with compound heterozygosity for R408 and Y414C mutations in phenylalanine hydroxylase (PAH) gene.

INTERVENTION(S)

Removal and testing for maternal mutation in PB1 and PB2 from each oocyte after standard IVF.

MAIN OUTCOME MEASURE(S)

DNA analysis of PB1 and PB2 indicating whether corresponding oocytes were mutation-free, for the purposes of transferring only unaffected embryos resulting from these oocytes.

RESULT(S)

Of 11 zygotes with both PB1 and PB2, 6 were predicted to be free of phenylketonuria. Of these, 4 were transferred, resulting in an unaffected twin pregnancy and birth of two healthy children.

CONCLUSION(S)

Preimplantation genetic diagnosis of phenylketonuria resulted in the birth of phenylketonuria-free children. Preimplantation genetic diagnosis by PB analysis in couples with a compound heterozygous male partner is clinically useful.

A comparison of different lysis buffers to assess allele dropout from single cells for preimplantation genetic diagnosis

Single cell polymerase chain reaction (PCR) for preimplantation genetic diagnosis (PGD) requires high efficiency and accuracy. Allele dropout (ADO), the random amplification failure of one of the two parental alleles, remains the most significant problem in PCR-based PGD testing since it can result in serious misdiagnosis for compound heterozygous or autosomal dominant conditions. A number of different strategies (including the use of lysis buffers to break down the cell and make the DNA accessible) have been employed to combat ADO with varying degrees of success, yet there is still no consensus among PGD centres over which lysis buffer should be used (ESHRE PGD Consortium, 1999). To address this issue, PCR amplification of three genes (CFTR, LAMA3 and PKP1) at different chromosomal loci was investigated. Single lymphocytes from individuals heterozygous for mutations within each of the three genes were collected and lysed in either alkaline lysis buffer (ALB) or proteinase K/SDS lysis buffer (PK). PCR amplification efficiencies were comparable between alkaline lysis and proteinase K lysis for PCR products spanning each of the three mutated loci (DeltaF508 in CFTR 90% vs 88%; R650X in LAMA3 82% vs 78%; and Y71X in PKP1 91% vs 87%). While there was no appreciable difference between ADO rates between the two lysis buffers for the LAMA3 PCR product (25% vs 26%), there were significant differences in ADO rates between ALB and PK for the CFTR PCR product (0% vs 23%) and the PKP1 PCR product (8% vs 56%). Based on these results, we are currently using ALB in preference to PK/SDS buffer for the lysis of cells in clinical PGD.

Is intracytoplasmic sperm injection itself an indication to perform preimplantation genetic diagnosis (PGD)? About PGD, invasive prenatal diagnosis and genetic sonography

Intracytoplasmic sperm injection (ICSI) provides the only sufficient treatment to overcome severe forms of male infertility. However, male infertility is linked to several genetic problems as an increased number of chromosomal aberrations, cystic fibrosis transmembrane conductance regulator gene mutations, Y-chromosome microdeletions, and androgen receptor mutations. Therefore, these couples are at a higher risk of transmitting genetic problems to their offspring compared to the general population. A proposed increased number of gonosomal aberrations in the offspring possibly results from the ICSI technique itself. This led in general to a worldwide agreement to counsel those couples to undergo invasive prenatal diagnosis in order to exclude chromosome abnormalities, especially gonosomal aberrations. In this paper the genetic risks of these couples and the possible implications of ICSI itself are discussed. Preimplantation genetic diagnosis may be considered a procedure of choice in these cases, but substantial ethical problems arise when such a screening is sought. An alternative procedure of prenatal diagnosis in these couples seems to be 'genetic sonography', i.e. high-resolution ultrasound with measurement of nuchal translucency at the end of the first trimester, and detailed fetal evaluation at 18-22 weeks of gestation.

A successful strategy for preimplantation genetic diagnosis of myotonic dystrophy using multiplex fluorescent PCR

The most common form of inherited muscular dystrophy in adults is myotonic dystrophy (DM), an autosomal-dominant disease caused by the expansion of an unstable CTG repeat sequence in the 3' untranslated region of the myotonin protein kinase (DMPK) gene. Expanded (mutant) CTG repeat sequences are refractory to conventional PCR, but alleles with a number of repeats within the normal range can be readily amplified and detected. Preimplantation genetic diagnosis (PGD) of DM has been successfully applied. However, a misdiagnosis using the reported protocol was recently documented. Two new PGD protocols for DM have been developed which utilise multiplex fluorescent PCR. Ideally a linked polymorphic marker, APOC2, is amplified in addition to the normal DMPK alleles, thus providing a back-up diagnostic result. However, the two couples reported in the present study were not fully informative at the APOC2 locus and so an unlinked short tandem repeat (STR) marker, D21S1414, was substituted. The highly polymorphic nature of the D21S1414, DMPK and APOC2 loci means that a very simple genetic fingerprint can be generated by analyses of these loci. This allows most DNA contaminants to be detected. Contamination is a significant problem for PGD and is the primary reason for the inclusion of D21S1414 and APOC2 in this protocol. This paper reports the first clinical experience and pregnancies following PGD for DM using a multiplex fluorescent PCR protocol.

Pre-implantation genetic diagnosis

Pre-implantation genetic diagnosis (PGD) was developed in the UK over 10 years ago. There are now more than 40 centres worldwide carrying out PGD and 150 babies have been born after genetic testing on day 3 of development, at the cleavage stage. This review covers the current status of PGD, the technology used and the types of genetically determined diseases for which testing has been developed.

Preimplantation diagnosis for Huntington's disease (HD): clinical application and analysis of the HD expansion in affected embryos

Huntington's disease (HD) is an autosomal dominant disease characterized by motor disturbance, cognitive loss and psychiatric manifestations, starting between the fourth and the fifth decade, followed by death within 10-20 years of onset of the disease. The disease-causing mutation is an expansion of a CAG triplet repeat at the 5' coding end of the Huntington gene. We have developed a single-cell PCR assay for the HD gene in order to propose preimplantation genetic diagnosis (PGD) for the couples at risk. We present here our first results with our first nine PGD cycles and also discuss the behaviour of the disease-causing expansion in pre-implantation embryos.