Intra-individual purifying selection on mitochondrial DNA variants during human oogenesis.

STUDY QUESTION: Does selection for mtDNA mutations occur in human oocytes? SUMMARY ANSWER: We provide statistical evidence in favor of the existence of purifying selection for mtDNA mutations in human oocytes acting between the expulsion of the first and second polar bodies (PBs). WHAT IS KNOWN ALREADY: Several lines of evidence in Metazoa, including humans, indicate that variation within the germline of mitochondrial genomes is under purifying selection. The presence of this internal selection filter in the germline has important consequences for the evolutionary trajectory of mtDNA. However, the nature and localization of this internal filter are still unclear while several hypotheses are proposed in the literature. STUDY DESIGN, SIZE, DURATION: In this study, 60 mitochondrial genomes were sequenced from 17 sets of oocytes, first and second PBs, and peripheral blood taken from nine women between 38 and 43 years of age. PARTICIPANTS/MATERIALS, SETTING, METHODS: Whole genome amplification was performed only on the single cell samples and Sanger sequencing was performed on amplicons. The comparison of variant profiles between first and second PB sequences showed no difference in substitution rates but displayed instead a sharp difference in pathogenicity scores of protein-coding sequences using three different metrics (MutPred, Polyphen and SNPs&GO). MAIN RESULTS AND THE ROLE OF CHANCE: Unlike the first, second PBs showed no significant differences in pathogenic scores with blood and oocyte sequences. This suggests that a filtering mechanism for disadvantageous variants operates during oocyte development between the expulsion of the first and second PB. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: The sample size is small and further studies are needed before this approach can be used in clinical practice. Studies on a model organism would allow the sample size to be increased. WIDER IMPLICATIONS OF THE FINDINGS: This work opens the way to the study of the correlation between mtDNA mutations, mitochondrial capacity and viability of oocytes. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by a SISMER grant. Laboratory facilities and skills were freely provided by SISMER, and by the Alma Mater Studiorum, University of Bologna. The authors have no conflict of interest to disclose.

EuMAR: a roadmap towards a prospective, cycle-by-cycle registry of medically assisted reproduction in Europe.

More than 20 years ago, the survey of activities in medically assisted reproduction (MAR) was initiated in Europe and resulted in cross-sectional annual reports, as issued by the European IVF Monitoring (EIM) consortium of ESHRE. Over time, these reports mirror the continuous development of the technologies and contribute to increased transparency and surveillance of reproductive care. Meanwhile, progressive changes of existing treatment modalities and the introduction of new technologies resulted in the need of a cumulative approach in the assessment of treatment outcomes, which warrants a prospective cycle-by-cycle data registry on MAR activities, including fertility preservation. This change in the paradigm of data collection in Europe towards the construction of cumulative outcome results is expected to generate additional insights into cross-institutional but also cross-border movements of patients and reproductive material. This is essential to improve vigilance and surveillance. The European monitoring of Medically Assisted Reproduction (EuMAR) project, co-funded by the European Union, will establish a registry for the transnational collection of prospective cycle-by-cycle MAR and fertility preservation data on the basis of an individual reproductive care code (IRCC). The rationale for the project and the objectives are presented here.

What next for preimplantation genetic screening?

Preimplantation genetic diagnosis for aneuploidy screening (preimplantation genetic screening-PGS) has been used to detect chromosomally normal embryos from subfertile patients. The main indications are advanced maternal age (AMA), repeated implantation failure, repeated miscarriages and severe male factor infertility. Many non-randomized PGS studies have been published and report an increase in implantation rate, and/or a decrease in miscarriage rate. Recently, two randomized controlled trials have been conducted on patients with AMA as the only indication. Neither study showed a benefit in performing PGS using live birth rate as the measure of success. The debate on the usefulness of PGS is ongoing; the only effective way to resolve the debate is to perform more well-designed and well-executed randomized clinical trials.

Intra-age, intercenter, and intercycle differences in chromosome abnormalities in oocytes.

OBJECTIVE: To determine the extent of intra-age and intercycle variations in the frequency of first polar body aneuploidy in two consecutive cycles of oocyte retrieval undertaken by the same patient within 1 year. DESIGN: Retrospective study. SETTING: Fertility centers. PATIENT(S): Infertile couples undergoing IVF. INTERVENTION(S): Patients underwent two consecutive cycles of preimplantation genetic screening through first polar body biopsy within 1 year. MAIN OUTCOME MEASURE(S): Meiosis I aneuploidy. RESULT(S): A total of 226 patients underwent 452 cycles of preimplantation genetic screening. Differences within age groups were wide, with 0-100% of oocytes being chromosomally normal in all age groups. Euploidy rates between centers were significantly different (48% vs. 25%). Intercycle differences for the same patient were also wide (0-100%), but with 68.5% of patients having less than ±2 euploid eggs of difference between cycles. CONCLUSION(S): Although euploidy rate decreased on average with advancing maternal age, the high intra-age and intercenter variation in oocyte chromosome abnormalities emphasize the difficulty in estimating how many euploid oocytes a specific woman will have. This may have repercussions for fertility preservation where a defined number of eggs are currently frozen just based on maternal age.

Artificial defocus for displaying markers in microscopy Z-stacks.

As microscopes have a very shallow depth of field, Z-stacks (i.e. sets of images shot at different focal planes) are often acquired to fully capture a thick sample. Such stacks are viewed by users by navigating them through the mouse wheel. We propose a new technique of visualizing 3D point, line or area markers in such focus stacks, by displaying them with a depth-dependent defocus, simulating the microscope's optics; this leverages on the microscopists' ability to continuously twiddle focus, while implicitly performing a shape-from-focus reconstruction of the 3D structure of the sample. User studies confirm that the approach is effective, and can complement more traditional techniques such as color-based cues. We provide two implementations, one of which computes defocus in real time on the GPU, and examples of their application.

Substandard application of preimplantation genetic screening may interfere with its clinical success.

The intent of this study was to evaluate a recent randomized clinical trial evaluating the effect of preimplantation genetic screening (PGS) that reports a negative effect on pregnancy outcome. This article reviews appropriate PGS techniques and how they differ from the trial in question. A closer look at the clinical trial in question reveals significant lack of expertise in biopsy, cell fixation, genetic analysis, and patient selection. At most, this trial demonstrates that in inexperienced hands, PGS can be detrimental. No other conclusions concerning the effect of PGS on pregnancy results can be drawn from the trial.

Increased rate of aneuploid embryos in young women with previous aneuploid conceptions.

OBJECTIVES: To determine whether a history of a previous aneuploid conception increases the rate of aneuploidy among women having preimplantation diagnosis (PGD). METHODS: Preimplantation embryos were tested for aneuploidy using FISH probes specific for chromosomes 13,15,16,17,18,21,22,X and Y. Using logistic regression to control for maternal age, we compared the rates of aneuploidy and other chromosome errors in 344 embryos from women having PGD because of a history of a previous aneuploid conception, 363 embryos from 42 women having PGD because of X-linked disorders and 1158 embryos from 135 women having PGD because of repeated in vitro fertilization failure. RESULTS: The frequency of aneuploidy differed significantly among patient groups for women younger than 35 (p = 0.003) but not for women older than 35. In women < 35, the rate of detected aneuploidy was 37.4% in the Aneuploid group, 20.9% in the X-linked group and 27.0% in the RIF group. (p = 0.0003 when the control groups are combined). The frequency of other chromosome abnormalities, as well as pregnancy and implantation rates, did not differ significantly among patient groups. CONCLUSIONS: This study suggests that a history of a trisomic pregnancy, whether or not it was a viable trisomy, is associated with an increased risk of another aneuploid conception at conception.