Current status of preimplantation diagnosis for single gene disorders

Etiologic, environmental and inherited risk factors in sarcomas

Sarcomas are a rare group of mesenchymal tumors affecting a younger population. The etiology remains unknown in most cases. Environmental factors that increase sarcoma risk include radiation exposure and chemical carcinogens. Several familial cancer syndromes confer sarcoma predisposition, such as the Li-Fraumeni Syndrome (LFS). In this increasingly genomic focussed era of medicine, it will be clinically important to understand the genetic basis of sarcoma risk.

Preimplantation genetic diagnosis for monogenic diseases: overview and emerging issues

Preimplantation genetic diagnosis (PGD) is an established reproductive option for couples at risk of conceiving a pregnancy affected with a known genetic disease, who wish to avoid an (additional) affected child, termination of pregnancy or recurrent miscarriages. Early technologies concentrated on different approaches to direct mutation testing for monogenic diseases using single cell PCR protocols, or sex selection by fluorescent in situ hybridization for X-linked monogenic disease. Development of multiplex fluorescent PCR allowed simultaneously testing of linked markers alongside the mutation test, increasing the accuracy by controlling for contamination and identifying allele drop-out. The advent of highly effective whole genome amplification methods has opened the way for new technologies such as preimplantation genetic haplotyping and microarrays, thus increasing the number of genetic defects that can be detected in preimplantation embryos; the number of cases carried out and the new indications tested increases each year. Different countries have taken very different approaches to legislating and regulating PGD, giving rise to the phenomenon of reproductive tourism. PGD is now being performed for scenarios previously not undertaken using prenatal diagnosis, some of which raise significant ethical concerns. While PGD has benefited many couples aiming to have healthy children, ethical concerns remain over inappropriate use of this technology.

Reiterative changes in the Italian regulation on IVF: the effect on PGD patients' reproductive decisions

National legislations represent one of the main factors influencing access to assisted reproduction treatment. The Italian situation in the last decade is an example of how the treatment of patients for preimplantation genetic diagnosis (PGD) was more dependent on regulators than on medical choices. This report analysed how the changes in Italian regulation affected the number of PGD referrals to this study centre, as well as their decision to opt for cross-border reproductive care (CBRC). The analysis showed that during the period in which PGD was actually not performed because of the restriction imposed by the Italian law on IVF (from 24 February 2004 to 7 May 2009) there was a significant decrease in the number of referrals asking for PGD (2.5% of total referrals) compared with the previous years (3.3%; P < 0.025) and following years when PGD was legalized (5.1%; P < 0.001). The number of couples opting for CBRC had an opposite trend, reaching a maximum when PGD was banned from Italian centres (55 couples), whereas after the readmission of PGD, only eight couples went abroad for treatment. Concomitantly, since May 2009, the proportion of couples performing a PGD cycle in this centre has constantly increased.

Breast cancer in the young: role of the geneticist

The genetics professional plays an important role in the care of young women with breast cancer by providing counseling on issues specific to these young women. The issues addressed in counseling include hereditary predisposition to cancer, fertility and reproductive options in the context of hereditary cancer, and the impact and implications of their history of early breast cancer on close family members. A thorough risk assessment and counseling session address the patient's personal and family history, with particular attention paid to benign and malignant findings that suggest the need for genetic testing. Genetics professionals, especially genetic counselors, also address the physical and emotional implications of an increased risk of cancer with patients and family members. This review highlights the unique aspects of care provided by these specialized healthcare providers.

PGD for monogenic disorders: aspects of molecular biology

Preimplantation genetic diagnosis (PGD) for monogenic diseases has known a considerable evolution since its first application in the early 1990s. Especially the technical aspects of the genetic diagnosis itself, the single-cell genetic analysis, has constantly evolved to reach levels of accuracy and efficiency nearing those of genetic diagnosis on regular DNA samples. In this review, we will focus on the molecular biological techniques that are currently in use in the most advanced centers for PGD for monogenic disorders, including multiplex polymerase chain reaction (PCR) and post-PCR diagnostic methods, whole genome amplification (WGA) and multiple displacement amplification (MDA). As it becomes more and more clear that when it comes to ethically difficult indications, PGD goes further than prenatal diagnosis (PND), we will also briefly discuss ethical issues.

Blastocyst trophectoderm biopsy and preimplantation genetic diagnosis for familial monogenic disorders and chromosomal translocations

OBJECTIVE

Modern in vitro fertilization practices involve transfer of embryos as blastocysts, when anabolic metabolism is well established and pregnancy rates can be maintained while transferring embryos singly to avoid multiple pregnancies. Embryo biopsy for preimplantation genetic diagnosis (PGD), however, is generally performed on day 3, when the embryo comprises just 6 to 8 cells, one or two of which are removed for testing. Implantation rates and clinical pregnancy rates have remained relatively low and a harmful effect from losing one or more cells from such early embryos has not been excluded.

METHODS

We performed a sequential study involving 399 egg retrievals and 1879 embryo biopsies for patients undergoing PGD to avoid a serious monogenic disease or an unbalanced chromosomal translocation. We compared implantation and viable pregnancy rates after biopsies taken on day 3 (cleavage-stage biopsy) with biopsies delayed until day 5 or 6, when the embryo is a blastocyst and 5 or more cells can be sampled from the trophectoderm while the inner cell mass, from which the fetus develops, remains intact. All embryos were transferred as blastocysts.

RESULTS

Despite fewer blastocysts than cleavage embryos biopsied and tested (3.6 compared to 6.6), implantation rates per embryo transferred were 43.4% if biopsied at the blastocyst stage and 25.6% if biopsied at the cleavage stage (P < 0.01), with ongoing or live-birth pregnancy rates per egg retrieval of 34.2% (average transfer number 1.1) for blastocyst biopsies and 25.5% (transfer number 1.6) for cleavage stage biopsies (P < 0.05, 1-tailed). The multiple pregnancy rate for monogenic disease exclusion fell from 16.7% to 2% (P = 0.04, 1-tailed).

CONCLUSIONS

For exclusion of genetic disease, day 5-6 blastocyst-stage biopsies are more likely to be followed by implantation and singleton births than is the case after PGD performed on day 3.

Preimplantation genetic diagnosis of X-linked retinoschisis

The aim of this study was to perform preimplantation genetic diagnosis (PGD) for X-linked retinoschisis using multiple displacement amplification (MDA) for whole genome amplification and linked markers to the RS1 gene. The study evaluates the ability of MDA to amplify the whole genome directly from a single blastomere. MDA products were used for polymerase chain reaction analysis of two polymorphic markers flanking the RS1 gene and a new X/Y marker, X22, to sex embryos in an X-linked retinoschisis PGD programme. Two couples in whom the wives were carriers of the RS1 gene mutation (599G-->A), previously identified in their families, were subjected to two PGD cycles each. The main outcome measure was the ability to analyse single blastomeres for X-linked retinoschisis using MDA. As a result, the development of an MDA-PGD protocol for X-linked retinoschisis allowed for the diagnosis of 20 embryos in the four PGD cycles performed. These were biopsied on day 3 of culture and analysed. Eight embryos were affected males and two embryos were female carriers. In summary, three healthy female and four healthy male embryos, and a female carrier embryo, were transferred 48 h after biopsy. One single pregnancy was achieved. This report shows that the MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD. It also allows the simultaneous amplification of different targets to perform diagnosis of any known gene defect and sexing test by standard methods and conditions.

Preimplantation genetic diagnosis of X-linked adrenoleukodystrophy with gender determination using multiple displacement amplification

OBJECTIVE

To evaluate the use of multiple displacement amplification (MDA) for whole genome amplification in the preimplantation genetic diagnosis (PGD) of X-linked adrenoleukodystrophy.

DESIGN

MDA was used to amplify the whole genome directly from a single blastomere. MDA products were used for polymerase chain reaction (PCR) analysis of two polymorphic markers flanking the ABCD1 gene and a new X/Y marker, X22, to sex embryos in an X-linked adrenoleukodystrophy PGD program.

SETTING

Fertility and gynecology private center in Alicante, Spain.

PATIENT(S)

A couple in which the wife is a carrier of the ABCD1 gene mutation (676A-->C) that was previously identified in her family.

INTERVENTION(S)

MDA of single blastomere and PCR tests for PGD.

MAIN OUTCOME MEASURE(S)

The ability to analyze single blastomeres for X-linked adrenoleukodystrophy using MDA.

RESULT(S)

The development of an MDA-PGD protocol for X-linked adrenoleukodystrophy allowed for the diagnosis of five embryos. These were biopsied on day 3 of culture and analyzed. One embryo was an affected male and one embryo was a female carrier. Three healthy female embryos were transferred 48 hours after biopsy. Unfortunately, no pregnancy was achieved.

CONCLUSION(S)

The MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD and allows the simultaneous amplification of different targets to perform a diagnosis of any known gene defect and a sexing test by standard methods and conditions.

Advantages of multiple markers and polar body analysis in preimplantation genetic diagnosis for Alagille disease

OBJECTIVE

The development of a preimplantation genetic diagnosis (PGD) protocol for Alagille syndrome (AGS), a rare autosomal dominant disorder with hepatic, cardiac and ophthalmologic involvement.

METHODS

We developed a polar body (PB)-based multiplex fluorescent PCR reaction for a female affected with AGS. The protocol included analysis of the Jagged 1 (JAG1) familial mutation and five closely linked highly polymorphic markers (D20S162, D20S901, D20S894, and D20S186).

RESULTS

In two cycles of PGD 9 of ten embryos were accurately diagnosed by assessment of first and second PBs, one embryo required additional blastomere biopsy.

CONCLUSIONS

This protocol takes advantage of the larger window of opportunity for transfer and the increased accuracy of diagnosis afforded by the combination of PB biopsy and multiple marker analysis. Two cycles resulted in the transfer of two and three mutation-free embryos and a subsequent pregnancy as measured by the rising hCG levels.

Preimplantation genetic diagnosis of Marfan syndrome using multiple displacement amplification

OBJECTIVE

To evaluate the use of multiple displacement amplification (MDA) for whole-genome amplification in the preimplantation genetic diagnosis (PGD) of Marfan syndrome.

DESIGN

Multiple displacement amplification was used to amplify the whole-genome directly from a single cell. The MDA product was used for polymerase chain reaction (PCR) analysis of five different loci. At this point MDA was used to develop a PGD-Marfan syndrome program.

SETTING

Fertility and gynecology private center in Alicante, Spain.

PATIENT(S)

A couple in which the husband is affected by Marfan syndrome and carries a novel mutation in the FBN-1 gene.

INTERVENTION(S)

The MDA of single cells and PCR tests for PGD.

MAIN OUTCOME MEASURE(S)

Allele drop-out (ADO), amplification efficiency rates, and the ability to detect Marfan syndrome using MDA.

RESULT(S)

We report that isothermal whole-genome amplification from single cells allowed analysis of five different loci using standard conditions. The development of a MDA-PGD protocol for Marfan syndrome allowed for the diagnosis of seven embryos. These were biopsied on day 3 of culture and analyzed. Two healthy embryos were transferred 48 hours after culture, resulting in a singleton ongoing pregnancy and the birth of a healthy child.

CONCLUSION(S)

The MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD. The use of MDA as a universal step marks a new cycle for PGD as it allows for the diagnosis of any known gene defect by standard methods and conditions.

Cancer genetic testing and assisted reproduction

PURPOSE

Because of increasing uptake of cancer genetic testing and the improving survival of young patients with cancer, health care practitioners including oncologists will increasingly be asked about options for assisted reproduction by members of families affected by hereditary cancer syndromes. Among these reproductive options, preimplantation genetic diagnosis (PGD) offers the opportunity to select embryos without familial cancer-predisposing mutations.

METHODS

A review of the published literature supplemented by a survey of PGD centers in the United States.

RESULTS

Prenatal diagnosis and/or embryo selection after genetic testing has already been performed in the context of more than a dozen familial cancer syndromes, including the common syndromes of genetic predisposition to colon and breast cancer.

CONCLUSION

While constituting new reproductive options for families affected by cancer, the medical indications and ethical acceptance of assisted reproductive technologies for adult-onset cancer predisposition syndromes remain to be defined. Continued discussion of the role of PGD in the reproductive setting is needed to inform the responsible use of these technologies to decrease the burden of heritable cancers.

Changing genetic world of IVF, stem cells and PGD. A. Early methods in research

Genetics proved essential to introduce IVF, preimplantation diagnosis (PGD) and embryo stem cells in the 1960s. Its small input in early years was confined to aspects such as timing follicle growth and ovulation. Modest understanding in the mid- to late 1980s, mostly on studies in mice, involved the actions of single genes and the balance between maternal and zygotic transcripts in preimplantation stages. Human IVF began after human oocytes were matured in vitro, and their meiotic chromosomes analysed. Their fertilization in vitro led to PGD and embryo stem cells. Unlike mouse embryos, most human embryos failed to implant, so the best had to be selected to improve IVF pregnancy rates. Initially, faster-growing embryos proved superior. Later, patterns of polarized nucleoli in pronuclei, the degree of blastomere fragmentation and growth of embryos in vitro to blastocysts provided excellent markers. Single cells could be isolated from embryos using micromanipulation. Stem cells from inner cell mass, a branch of IVF, differentiated into immortal stem cell lines in vitro if disaggregated. They formed virtually all body tissues in blastocysts cultured intact or when injected singly into recipient blastocysts. Later, the genetic controls of ES cell differentiation were assessed, together with factors switching them along specific differentiation pathways. Marker genes identified ES cells differentiating into various tissues.

Pregnancies and live births after trophectoderm biopsy and preimplantation genetic testing of human blastocysts

OBJECTIVE

To compare multiple-cell trophectoderm biopsy for preimplantation genetic diagnosis (PGD) from day-5 blastocysts with previously published experience with day-3 cleavage-stage embryos.

DESIGN

Retrospective review of laboratory and clinical experience.

SETTING

Sydney IVF, a private clinic in Australia.

PATIENT(S)

Preimplantation genetic diagnosis (PGD) patients age < 44 years with at least one IVF blastocyst suitable for biopsy, recruited from January 2002 through August 2004.

INTERVENTION(S)

Biopsy of trophectoderm from blastocysts on day 5 or 6, with same-day PGD for mutation testing, translocation testing, aneuploidy screening or sex selection. Spare, normal biopsied blastocysts were cryostored for possible later transfer.

MAIN OUTCOME MEASURE(S)

Fetal heart-positive pregnancy rate and accumulating live birth rate after adding results from biopsied fresh and frozen blastocysts for particular couples.

RESULT(S)

In 231 started PGD treatment cycles, unambiguous results were obtained from 974 of 1,050 biopsied blastocysts (93%); all blastocysts survived the biopsy procedure by reconstitution of their blastocele. One hundred nineteen women (median age, 36 years) have had 127 blastocysts transferred fresh (fetal heart-positive implantation rate, 41%). Of 146 blastocysts cryostored, 27 have been thawed (all with > 50% cell survival) and 24 transferred (implantation rate, 26%). To date, 53 pregnancies have been delivered or are ongoing, with an additional 4 clinical miscarriages (7%) and 6 subclinical miscarriages (total miscarriage rate, including biochemical pregnancies, 16%). There were no twin pregnancies.

CONCLUSION(S)

With technically appropriate blastocyst culture and freezing, blastocyst biopsy and cryostorage and later transfer of biopsied blastocysts is shown to be a practical and probably preferable path to preimplantation genetic testing of embryos compared with cleavage-stage embryo biopsy, being accompanied by a high implantation rate (and hence more conducive to elective single embryo transfer) and by a low rate of twinning and miscarriage.

Generation of a human embryonic stem cell line encoding the cystic fibrosis mutation deltaF508, using preimplantation genetic diagnosis

Human embryonic stem (hES) cells are pluripotent cells isolated from early human embryos. They can be grown in vitro and made to differentiate into many different cell types. These properties have suggested that they may be useful in cell replacement therapy for many degenerative diseases. However, if hES cells could also be manufactured with mutations significant in human disease, they could provide a powerful in-vitro tool for modelling disease processes and progression in a number of different cell types, as well as providing an ideal system for studying in-vitro toxicity and efficacy of drugs and other therapeutic systems such as gene therapy. Embryos with such mutations are generated as part of routine genetic testing during preimplantation genetic diagnosis, providing the opportunity to generate cell lines with significant mutations. A human embryonic stem cell line homozygous for the most common mutation leading to cystic fibrosis in humans (delta F508) has been generated and characterized. This cell line has the same morphology and expresses proteins typical of other unaffected hES cell lines. This cell line represents an important in-vitro tool for understanding the pathophysiology of cystic fibrosis, and presents exciting opportunities to test the efficacy and toxicity of new therapies relevant to CF.

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.

Averting abnormal inheritance: potential of gene therapy and preimplantation diagnosis

Serious inherited disease in children can be averted by preimplantation genetic diagnosis (PGD) and potentially by gene therapy in addition to prenatal diagnosis. PGD is now well established and provides a secure, if expensive and complex form of care. Gene therapy has been practised only in animals, although its success in alleviating various conditions in adults and newborns, together with the scientific drive of the genome project, make it a highly likely approach over coming years. Pros and cons of both approaches are contrasted and compared. Newer reproductive techniques such as somatic cell hybridization promise to add new dimensions to gene therapy, and could be combined with PGD. This paper discusses the finer details of these options, their safety and the ethical issues they have raised.