Sex determination of human embryos using the polymerase chain reaction and confirmation by fluorescence in situ hybridization

Human embryos from induced pluripotent stem cell-derived gametes: ethical and quality considerations

Protocols for successful differentiation of male and female gametes from induced pluripotent stem cells have been published. Although culture of precursor cells in a natural microenvironment remains necessary to achieve terminal differentiation, the creation of human preimplantation embryos from induced pluripotent stem cell-derived gametes is technically feasible. Such embryos could provide a solution to the scarcity of human cleavage-stage embryos donated for research. Here, we discuss current technology, major research-related ethical concerns and propose the norms that would assure the quality and reliability of such embryos.

Safety paradigm: genetic evaluation of therapeutic grade human embryonic stem cells

The use of stem cells for regenerative medicine has captured the imagination of the public, with media attention contributing to rising expectations of clinical benefits. Human embryonic stem cells (hESCs) are the best model for capital investment in stem cell therapy and there is a clear need for their robust genetic characterization before scaling-up cell expansion for that purpose. We have to be certain that the genome of the starting material is stable and normal, but the limited resolution of conventional karyotyping is unable to give us such assurance. Advanced molecular cytogenetic technologies such as array comparative genomic hybridization for identifying chromosomal imbalances, and single nucleotide polymorphism analysis for identifying ethnic background and loss of heterozygosity should be introduced as obligatory diagnostic tests for each newly derived hESC line before it is deposited in national stem cell banks. If this new quality standard becomes a requirement, as we are proposing here, it would facilitate and accelerate the banking process, since end-users would be able to select the most appropriate line for their particular application, thus improving efficiency and streamlining the route to manufacturing therapeutics. The pharmaceutical industry, which may use hESC-derived cells for drug screening, should not ignore their genomic profile as this may risk misinterpretation of results and significant waste of resources.

Effect of karyotype on successful human embryonic stem cell derivation

The success rate of human embryonic stem cell (hESC) derivation depends on both culture conditions and embryo quality and is routinely determined by morphological criteria. However, high incidence of chromosomal abnormality even in high-grade cleavage embryos from in vitro fertilization (IVF) patients suggests that the morphological grade of supernumerary embryos obtained from IVF clinics may not be a good prediction factor for successful hESC derivation. We show here that from one donor under identical derivation conditions 12 karyotypically abnormal post-bioptic embryos did not yield hESC lines, whereas two out of four normal embryos did. This suggests that the capacity of embryos to give rise to hESC line is likely to be influenced by their genetic status.

Intracytoplasmic sperm injection (ICSI)--what are the risks?

In vitro fertilization used in combination with intracytoplasmic sperm injection allows otherwise sterile couples to become parents. Despite recent studies on the safety of these technologies, there is still only an incomplete picture of the risks associated with the usage of these assisted reproductive techniques to offspring. The risk of multiple gestations continues to be of major concern because of its association with low birth weight, preterm delivery, and increased perinatal mortality. This article outlines the risks associated with in vitro fertilization/intracytoplasmic sperm injection as a well-defined treatment for couples with severe male factor infertility.

Mutation and haplotype analysis for Duchenne muscular dystrophy by single cell multiple displacement amplification

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder with mutational heterogeneity. The scarcity of DNA from single cells in preimplantation genetic diagnosis (PGD) for DMD limits comprehensive genetic testing. Multiple displacement amplification (MDA) is reported to generate large amounts of template and give the most complete coverage and unbiased amplification to date. Here, we developed mutation and haplotype analysis in conjunction with gender determination on MDA products of single cells providing a generic approach that widens availability of PGD for female carriers with varied mutations. MDA amplified with 98.5% success for single lymphocytes and 94.2% success for single blastomeres, which was evaluated on 60 lymphocytes and 40 blastomeres. A total of six commonly mutant exons, eight short tandem repeat markers within dystrophin gene and amelogenin were incorporated into subsequent singleplex PCR assays. The mean allele dropout rate was 9.0% for single lymphocytes and 25.5% for single blastomeres. None of the blank controls gave a positive signal. Genotyping of each pedigree for three families provided 2-3 fully informative alleles per dystrophin haplotype besides specific mutant exons and amelogenin. We suggest that this approach is reliable to identify non-carrier female embryos other than unaffected male embryos and reduce the risk of misdiagnosis.

The use of preimplantation genetic diagnosis in sex selection for family balancing in India

This paper describes the use of preimplantation genetic diagnosis (PGD) in sexing embryos for family balancing in a private IVF clinic in India from April 1999 to April 2001. Embryos were biopsied and analysed on day 3, cultured in sequential media and then transferred on day 4 or day 5 after morphological selection of the best embryos. From a total of 42 cycles started, 14 clinical pregnancies and nine live births have been achieved so far, with five ongoing pregnancies. The benefits of delayed transfer 24-48 h after the embryo biopsy are that PGD centres could use the extra time available to confirm the diagnosis or introduce additional diagnostic tests for the same embryo. The selection of blastocysts for transfer should also permit the transfer of fewer embryos, thus reducing the risk of multiple gestations and increasing the pregnancy rate as a consequence of the expected higher implantation rate. This is the first report of the use of PGD in sex selection for family balancing in India, where couples place a premium on having baby boys, and the social and ethical aspects of the use of this technology in this setting are briefly discussed.

Genetics, age, and infertility

OBJECTIVE

To review the genetics of aging specifically as it pertains to human fertility, as well as the recent advancements in the diagnosis of genetic diseases prior to embryo implantation.

METHODS

A review of our own experience as well as the scientific literature with regards to the decline in female fertility with age, the success of IVF in women of older reproductive age, and the role of preimplantation genetic diagnosis (PGD) in the evaluation of the patient at risk for fetal genetic anomalies.

RESULTS

The decline in female fertility occurs primarily as a result of a decline in oocyte quality as well as quantity. The frequency of chromosomal anomalies in recognized abortuses increases in parallel with the age-specific rise in the incidence of spontaneous abortions. PGD is an accurate diagnostic tool for exclusion of genetically deficient embryos prior to initiation of pregnancy.

CONCLUSION

Reproductive failure in women of older age appears to be directly related to ovarian age. Recent techniques such as cytoplasmic or germinal vesicle transfer are designed to replace the senescent cellular machinery believed to be responsible for genetic errors that occur during early cell division. PGD can accurately identify embryos with genetic deficiencies prior to implantation.

Preimplantation genetic diagnosis of human embryos for Marfan's syndrome

PURPOSE

Single-cell nested polymerase chain reaction (PCR) and Ddel endonuclease digestion were used to detect the presence of a Marfan's syndrome mutation in human preimplantation embryos derived from in vitro fertilization (IVF). These procedures were conducted to eliminate the possibility of transmission of the affected allele from the father to his offspring. The mutation on chromosome 15 is transmitted as an autosomal dominant trait, and the chance of having a child affected with the disease is 50%.

METHODS

A couple presented to the Program for In Vitro Fertilization, Reproductive Surgery and Infertility for preimplantation genetic diagnosis. IVF was performed and embryo biopsy was done on day 3 embryos. Single blastomeres were removed from embryos and subjected to nested PCR analysis and endonuclease digestion to detect a Marfan's syndrome mutation located on chromosome 15 inherited from the father.

RESULTS

Thirteen oocytes were injected with spermatozoa using intracytoplasmic sperm injection, and nine fertilized normally. Following embryo biopsy and polymerase chain reaction amplification-Ddel endonuclease digestion, five embryos were detected that were positive for the mutation. The four non-affected embryos were transferred to the uterus, resulting in a healthy and normal ongoing pregnancy.

Chromosomal analysis of early fetal losses in relation to transvaginal ultrasonographic detection of fetal heart motion after infertility

OBJECTIVE

To evaluate the prognostic value of transvaginal ultrasound (TVUS) detection of fetal heart motion (FHM) in view of maternal age and chromosomal analysis of spontaneously aborted fetal tissue.

DESIGN

A 3-year retrospective, descriptive study.

SETTING

Two medical center-based infertility-care facilities.

PATIENT(S)

336 pregnancies were initiated by intrauterine insemination or embryo transfer for women of reproductive age who were seeking infertility treatment.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

beta hCG levels measured > 40 mIU/mL at 4-5 weeks' gestation and were followed by an initial TVUS at 5-8 weeks. Of these pregnancies, 52 ended in a first trimester loss. Twenty were defined by failure to detect FHM by 7 weeks' gestation (Group I), and 32 were marked by the loss of prior FHM at a mean of 2.6 weeks later (Group II). Fetal tissue was removed by dilatation and suction curettage. Cytogenetic studies were performed from short-term cultures of dissected chorionic villi and/or sac.

RESULT(S)

Chromosomal aberrations were found in 75.0% of abortuses in Group I and 65.6% in Group II. Different types of chromosomal abnormalities were present in each these groups. The maternal age-related trisomies which can progress to term (i.e., 13, 18, 21) were associated with early TVUS detection of FHM. The frequency of chromosomal abnormalities varied significantly with maternal age, with normal fetal karyotypes in 7 of 11 (63.6%) women < 35 years, but only in 9 of 41 (22.0%) women > or = 35 years despite the detection of FHM in 24 of 41 (58.5%) of these older women. Detection of FHM was associated with pregnancies continuing beyond the first trimester in 284 of 316 (90.0%) overall, but differed significantly with age (166 of 174 [95.4%] women < 35 years vs. 118 of 142 [83.1%] women > or = 35 years).

CONCLUSION(S)

Although the occurrence of chromosomal abnormalities in spontaneous demises did not differ according to TVUS detection of FHM, the types of aberrations were distributed differently. Since maternal age remains a significant factor in early fetal loss, TVUS detection of FHM should not be as reassuring for women > or = 35 years as for younger women.

Update in preimplantation genetic diagnosis. Age, genetics, and infertility

PGD has been successfully used for several years. Over 40 babies have been born worldwide by use of these techniques. Unfortunately, a number of misdiagnoses have been made, a distressing consequence of a new frontier. Significant advances have been made to improve the efficiency and accuracy of PCR and FISH. The widespread use of this technology awaits further documentation of safety and accuracy. Other issues must also be addressed. First, the cost-effectiveness of the techniques relative to the traditional alternatives must be evaluated. A number of ethical issues regarding embryo screening must be addressed including what diseases are serious enough to warrant the procedure. Another concern is the use of this technology for nongenetic disorders such as gender selection. Finally, the experimental nature of these procedures must continually be discussed with patients, and long-term follow-up studies must be undertaken. Development of more accurate and less expensive assays coupled with improved IVF success rates may make PGD a more widely used clinical tool. The future awaits these developments.

Obstetric outcome of pregnancies resulting from embryos biopsied for pre-implantation diagnosis of inherited disease

OBJECTIVE

Pre-implantation diagnosis of inherited disease is now a viable option for some couples at risk of transmitting inherited disorders to their children. Since the pregnancy begins knowing that the embryo is not at risk, the need for repeated terminations is eliminated. Up to 25% of the embryo is removed during the procedure, and so it is important to study the resulting pregnancies. Here we report on the obstetric outcome of our first 16 pregnancies resulting from embryo biopsy and preimplantation diagnosis of inherited disease.

SETTING

Teaching hospital.

SAMPLE

The first 16 pregnancies (12 singletons and 4 twins) following pre-implantation diagnosis.

RESULTS

Three singleton pregnancies were lost in the first trimester. Of the remaining pregnancies, two had no prenatal diagnosis, six cases of X-linked disease had the sex confirmed by ultrasound and chorionic villus sampling was performed in the remaining five. All the singleton pregnancies had an uneventful antenatal course and the birthweights and Apgar scores of the babies were normal. The twin pregnancies presented obstetric complications but these were not unusual.

CONCLUSIONS

Fifteen healthy infants were born, but for the foreseeable future pre-implantation diagnosis pregnancies should be closely followed up.

Influence of mosaicism on sexing of human preembryos detected by the polymerase chain reaction

PURPOSE

Preimplantation sex determination using a single cell by the polymerase chain reaction (PCR) was investigated to elucidate the influence of mosaicism.

METHODS

The SRY and ZFX genes were coamplified as target sequences for the Y and X chromosomes, respectively. The sensitivity of the single and nested PCR method was examined initially followed by amplification of single amniocytes by the nested PCR. Then the sex of single blastomeres at the three- and nine-cell stages was determined by the nested PCR.

RESULTS

The nested PCR was 10(4)-fold more sensitive than the single PCR. Sex determination was possible in 97.5% (117/120) of the blastomeres tested. However, the correspondence rate for all blastomeres within a single embryo was only 60% (12/20 embryos). Among the remaining embryos for which sexing of all blastomeres was not consistent, only one blastomere showed findings indicating the presence of mosaicism (or pseudomosaicism).

CONCLUSIONS

At least two blastomeres need to be assessed when determining the sex of an embryo in order to avoid misdiagnosis due to mosaicism (or pseudomosaicism).

Pregnancies resulting from embryos biopsied for preimplantation diagnosis of genetic disease: biochemical and ultrasonic studies in the first trimester of pregnancy

PURPOSE

Our purpose was to investigate early biochemical and ultrasonic measurements of pregnancies resulting from embryos biopsied for preimplantation diagnosis of inherited disease.

RESULTS

Singleton pregnancies following biopsy had lower initial hCG levels [10 or 12 days after oocyte recovery (OR)], which rose steeply to match the controls by 16 days after OR. Twin biopsied pregnancies showed hCG levels lower than those of twin control pregnancies, which rose in parallel with the controls but remained lower for a longer period than the singletons. Progesterone levels showed a wide variation. Ultrasound measurements showed that overall the mean sac diameter and crown-rump length at 28 and 42 days after egg collection were similar in biopsied and control pregnancies.

CONCLUSIONS

Pregnancies resulting from biopsied embryos behave similarly to control IVF pregnancies. However, the reduction in cell mass following embryo biopsy occasionally results in reduced levels of circulating serum hCG and smaller ultrasound measurements in early pregnancy.

Preimplantation diagnosis of inherited disease by embryo biopsy: an update of the world figures

PURPOSE

Cleavage stage embryo biopsy and preimplantation diagnosis was first reported five years ago. The annual collation of the world figures for centres offering this procedure is important to continually assess the efficiency and success of the biopsy, diagnosis and pregnancies obtained.

MATERIALS AND METHODS

Data was collected from 14 centres worldwide. The largest series of diagnosis has been performed for those patients carrying X-linked disease where the embryos have been sexed either by PCR or FISH. PCR has also been used for the specific diagnosis of a number of single gene defects, mainly for cystic fibrosis but also for the diagnosis of Lesch Nyhan syndrome, Fragile X, Duchenne muscular dystrophy, Tay Sachs, haemophilia and RhD blood typing.

RESULTS

For PCR sexing, a total of 62 cycles have been performed with 14 pregnancies, 8 deliveries and 11 babies born. For FISH sexing, 70 cycles have resulted in 15 pregnancies, 8 deliveries and 11 babies born. For the specific diagnosis of single genes defects, a total of 65 cycles resulted in 21 pregnancies, 12 deliveries and 12 babies born. Overall, 197 cycles were performed, with 171 embryo transfers (86%), 50 pregnancies (25% per cycle, 29% per transfer), 28 deliveries and 34 babies born.

CONCLUSIONS

New methods are being developed to increase the scope of preimplantation diagnoses that can be offered. From next year, the biochemical and miscarriage rates will also be recorded.

Recent advances in reproductive genetic technologies

New possibilities for the diagnosis and treatment of reproductive and genetic disorders are becoming available as a result of a series of recent technical advances. Intracytoplasmic sperm injection (ICSI) allows treatment of numerous infertile men whose sperm cannot penetrate the egg to initiate fertilization. Molecular genetic testing provides clients of reproductive age with additional information that permits prevention of genetic diseases such as fragile X syndrome, the leading cause of inherited mental retardation. Preimplantation genetic testing (PGT) offers couples who carry genetic disorders the prospect of having children with a greatly decreased risk of initiating a pregnancy involving an affected individual. Flow-cytometric sperm separation offers a new, effective approach for prevention of X-linked genetic disorders. Two major causes of recurrent pregnancy loss (RPL) involve recurrent trisomies and immunological disorders. Of the latter, 70% of studied populations of patients can attain live births with simple treatment protocols. Maternal serum assays involving multiple markers reduce both false positives and false negatives in detection of trisomies. Despite these advances in research, many safe and effective methods of diagnosis and treatment remain under-utilized in the clinical arena.

Assessment of numeric abnormalities of X, Y, 18, and 16 chromosomes in preimplantation human embryos before transfer

OBJECTIVE

Our purpose was to determine the feasibility of ascertaining aneuploidy for chromosomes X, Y, 18, and 16 by use of multiple-probe fluorescence in situ hybridization in blastomeres from preimplantation human embryos.

STUDY DESIGN

A short fluorescence in situ hybridization procedure involving the simultaneous use of four deoxyribonucleic acid probes detected with red, green, blue, or a mixture of red and green fluorochromes was developed to determine numeric abnormalities of chromosomes X, Y, 18, and 16. Embryos underwent biopsy, and all or most cells were analyzed to distinguish true aneuploidy from mosaicism and to assess technique variations within the same embryo (n = 64).

RESULTS

The analysis of all the blastomeres of an embryo was achieved in 91% of the embryos. Successful analyses including biopsy, fixation, and fluorescence in situ hybridization were achieved in 87.8% of the blastomeres. Of the four chromosomes tested, numeric aberrations were found in 23% and 42% of normally and abnormally developing embryos, respectively, including aneuploidy, polyploidy, haploidy, and mosaicism. When diploid embryos containing one or several tetraploid cells are counted as chromosomally abnormal, then 49% and 61% of normally and abnormally developing embryos, respectively, were chromosomally abnormal. Aneuploid embryos consisted of two monosomies for chromosome 16, one for chromosome 18, and a trisomy for chromosome 16. There was a tendency for aneuploidy to increase with maternal age.

CONCLUSIONS

Fluorescence in situ hybridization is a more efficient method than cytogenetic analysis to study specific aneuploidies at preimplantation stages of development in human embryos. In addition, the preimplantation genetic diagnosis of two blastomeres per eight-cell embryo may be sufficient to ensure successful analysis of polyploidy, haploidy, and specific aneuploidies without endangering the survival of the embryo. The technique can be easily modified to consider other chromosomes, including 13 and 21. Because most chromosomally abnormal embryos do not develop to term, the use of this technique may increase the delivery rate per embryo by allowing only transfer of embryos normal for the tested chromosomes. This technique would be most useful for older women undergoing in vitro fertilization, because aneuploidy appears to increase with advancing maternal age.

The new eugenics and medicalized reproduction

We know today that classical eugenics, of an essentially negative nature, was not only an aggressive and brutal practice but, like its positive counterpart, inefficient as well. In fact, numerous biological, sociological, and psychological events beyond our control arise to prevent the realisation of any eugenic plan. Thus, like all human beings, individuals whose procreation is encouraged by positive eugenics suffer unexpected mutations that are transmitted to their offspring by their gametes. Gene distribution among the gametes at meiosis is the result of an uncontrollable, natural lottery. As an effect of this lottery, positive eugenics could allow the birth of defective babies whereas negative eugenics precludes the birth of normal babies.