Cytogénétique des ovocytes humains : 40 ans de progrès

Follicular fluid protein content (FSH, LH, PG4, E2 and AMH) and polar body aneuploidy

PURPOSE

Our objective was to identify a marker for oocyte aneuploidy in follicular fluid (FF) in women with an increased risk of oocyte aneuploidy after controlled ovarian hyperstimulation.

MATERIALS AND METHODS

Three groups of oocytes were constituted for polar body screening by FISH (chromosomes 13, 16, 18, 21 and 22): Group 1, advanced maternal age (n = 156); Group 2, implantation failure (i.e. no pregnancy after the transfer of more than 10 embryos; n = 101) and Group 3, implantation failure and advanced maternal age (n = 56). FSH and other proteins were assayed in the corresponding FF samples.

RESULTS

Of the 313 oocytes assessed, 35.78 % were abnormal. We found a significant difference between the follicular FSH levels in normal oocytes and abnormal oocytes (4.85 ± 1.75 IU/L vs. 5.41 ± 2.47 IU/L, respectively; p = 0.021). We found that the greater the number of chromosomal abnormalities per oocyte (between 0 and 3), the higher the follicular FSH level.

CONCLUSION

High FF FSH levels were associated with oocyte aneuploidy in women having undergone controlled ovarian hyperstimulation.

Delay in oocyte aging in mice by the antioxidant N-acetyl-L-cysteine (NAC)

BACKGROUND

Ovarian aging is associated with declining numbers and quality of oocytes and follicles. Oxidative stress by reactive oxygen species (ROS) contributes to somatic aging in general, and also has been implicated in reproductive aging. Telomere shortening is also involved in aging, and telomeres are particularly susceptible to ROS-induced damage. Previously, we have shown that antioxidant N-acetyl-L-cysteine (NAC) effectively rescues oocytes and embryos from ROS-induced telomere shortening and apoptosis in vitro. Using mice as models, we tested the hypothesis that reducing oxidative stress by NAC might prevent or delay ovarian aging in vivo.

METHODS

Initially, young females were treated with NAC in drinking water for 2 months and the quality of fertilized oocytes and early embryo development were evaluated. Next, young mice 1-1½ months old were treated for 1 year with NAC added in drinking water, and their fertility was analyzed starting at 6 months, as indicated by litter size, oocyte number and quality. The ovaries were also examined for telomere activity and length and the expression of selected genes related to aging and DNA damage.

RESULTS

Short-term treatment of mice for 2 months with NAC demonstrated that NAC improved the quality of fertilized oocytes and early embryo development. Mice treated with a long-term low concentration (0.1 mM) of NAC had increased litter sizes at the ages of 7-10 months compared with age-matched controls without NAC treatment. NAC also increased the quality of the oocytes from these older mice. Moreover, the expression of sirtuins was increased, telomerase activity was higher and telomere length was longer in the ovaries of mice treated with NAC compared with those of the control group.

CONCLUSIONS

These data suggest that appropriate treatment with the antioxidant NAC postpones the process of oocyte aging in mice.

Pertinence of apoptosis markers for the improvement of in vitro fertilization (IVF)

In assisted reproductive technology (ART), the pregnancy and birth rates following in vitro fertilization (IVF) attempts are still low. Recently, apoptotic markers have been suggested as new criteria for oocyte and embryo quality selection. Many studies have provided evidence that poor oocyte and embryo quality can be associated with apoptosis. The aim of this review is to summarize our current knowledge on the apoptotic process in oocytes and embryos, and focus on the possibility for using apoptotic markers as a reliable and predictive marker to select competent oocytes and embryos during IVF. Moreover, it is currently accepted that IVF failures, linked to poor embryo quality, are, in part, associated with suboptimal in vitro culture conditions. Here, we also review the current state of knowledge concerning how the genetic control of apoptosis during folliculogenesis and pre-implantation embryonic development is affected by in vitro culture conditions during IVF. In the future, identification of apoptotic markers in ART for oocyte and embryo selection should result in the development of new agonistic or antagonistic molecules of apoptosis by medicinal chemistry.

Monozygotic twins discordant for trisomy 21 and maternal 21q inheritance: a complex series of events

We report on a monochorionic/diamniotic twin pregnancy discordant for trisomy 21. Amniocentesis (at 13(5/7) weeks) was performed following ultrasound signs of hydrops and cystic hygroma in twin 1 (T1). Prenatal karyotype showed non-mosaic trisomy 21 in T1 (47,XX,+21[7]), and low-grade mosaic trisomy 21 in twin 2 (T2) (47,XX,+21[2]/46,XX[19]). Post mortem examination of fetal skin, kidneys and lungs confirmed trisomy 21 in T1 (47,XX,+21[548]) and the placenta (47,XX,+21[200]). T2 had a normal karyotype (46,XX[648]). Analysis of microsatellite polymorphisms in multiple samples from the placenta, hand, lungs, kidneys and the umbilical cords of both twins confirmed monozygosity for all loci tested, and trisomy 21 in T1. Unexpectedly, T1 and T2 inherited different maternal alleles for markers of the most distal 4 Mbp of 21q. At least four successive events are needed to explain the genetic status of both twins and include maternal MI premature chromatids separation or maternal II meiotic nondisjunction and post-zygotic events such as, chromosome rescue, nondisjunction, an/or recombination.

Possible risk factors for Down syndrome and sex chromosomal aneuploidy in Mysore, South India

BACKGROUND

Down syndrome (DS) and sex chromosomal aneuploidy (SA) are common chromosomal anomalies causing congenital malformations and mental retardation in humans. The well-established risk factor, advanced maternal age, was not found in many of the DS and SA cases in India, while the other possible risk factors have not been well studied. In view of this, the present study has been made.

MATERIALS AND METHODS

During the last 5 years, 150 clinically suspected DS and 25 SA cases were referred to our laboratory for chromosome investigation from major hospitals of Mysore city. Chromosome preparations were made from these patients after informed consent was obtained. Well-spread G-banded metaphase plates were analyzed by automated LEICA KARYO software. Two hundred and 100 randomly selected families belonging to different religions were used as controls for the DS and SA cases, respectively. Statistical analysis was carried out using logistic regression

RESULTS

Out of the 150 cases of DS, 122 had free trisomy 21, two were mosaic trisomy 21, and one had translocation. Logistic regression of case-control study of DS children revealed that the odds ratio of uncle-niece marriages, or second cousin marriages, or parents lived in rural region, or exposure of the parents to chemicals, or parents education status, or habits (tobacco/ alcohol used) of father, or mother not undergone prenatal scanning, or mothers with previous abortions were significant when all the variables of that category were used one at a time. Exposure of the parents to chemicals, parents' educational status, habits (tobacco/alcohol use) of the father, mother not undergone prenatal scanning, and history of previous abortions were significant when all the variables of that category were used one at a time. Similarly, except for consanguinity, history of previous abortions, and mother not undergone prenatal scanning, all other factors showed significant odds ratios in SA cases.

CONCLUSION

Besides the known risk factors, consanguinity, region (rural/urban) of residence of parents, exposure of parents to chemicals, educational status of parents, habits of father, prenatal scanning, and reproductive performance of mother are possible risk factors for chromosomal aneuploidy.

Oocyte karyotyping by comparative genomic hybridization [correction of hybrydization] provides a highly reliable method for selecting "competent" embryos, markedly improving in vitro fertilization outcome: a multiphase study

OBJECTIVE

To assess the karyotypic relationship between prefertilized/postfertilized oocytes and embryos using comparative genomic hybridization (CGH) on polar body-1 (PB-1), PB2, and blastomere biopsies and to evaluate IVF outcomes after transfer of blastocysts derived from euploid oocytes.

DESIGN

Prospective cohort.

SETTING

Medical center.

PATIENT(S)

Phase1: Fourteen oocyte donors (23-29 years). Phase 2: Forty-one healthy embryo recipients aged 29-43 years free of endometrial implantation dysfunction. In 30 cases own eggs were used. Eleven women used donated oocytes.

INTERVENTION(S)

Phase 1: PB-1 biopsies followed intracytoplasmic sperm injection (ICSI), PB-2, and day 3 blastomere biopsies. Phase 2: PB-1 biopsy followed by ICSI using normal sperm and the subsequent embryo transfer of < or =2 blastocysts derived from euploid oocytes. Comparative genomic hybridization on all DNA derived from phase 1 and 2 biopsies.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rate.

RESULT(S)

Phase 1: 39% of oocytes and 88% of zygotes were euploid; >95% progressed to blastocysts. Mosaicism as evidenced by euploid oocytes developing into aneuploid zygotes or embryos occurred in 13% of concepti. Phase 2: Six of 30 women using own eggs, who failed to produce euploid oocytes, were cancelled. Thirty-five women underwent embryo transfers with < or =2 (mean, 1.3 +/- 0.7) blastocysts derived from euploid oocytes. The ongoing pregnancy/implantation rates per embryo transfer were 74% and 82%, respectively.

CONCLUSION(S)

Transferring euploid embryos markedly improved IVF outcome. These findings, if corroborated, could initiate a paradigm shift in assisted reproductive technology (ART).