Diagnostic prénatal et diagnostic pré-implantatoire : arbre décisionnel, nouvelles pratiques ?

Le diagnostic pré-implantatoire (DPI) a pour objectif l’étude des caractéristiques génétiques d’un embryon âgé de trois jours. Il offre ainsi à des couples ayant un risque élevé de transmettre une maladie héréditaire une alternative au diagnostic prénatal (DPN). Si, au début de son application, les pathologies et les couples pris en charge ainsi que le cadre réglementaire du DPI étaient très proches de ceux du DPN, des indications propres au DPI émergent peu à peu. Les pathologies prises en charge, notamment, se diversifient, en particulier dans les pays où l’absence de réglementation autorise toutes les pratiques. Certaines de ces applications ne sont d’ailleurs pas sans poser de sérieux problèmes éthiques. Même en France, où cette activité est particulièrement encadrée, la récente modification de la loi reflète cette évolution.Preimplantation genetic diagnosis (PGD) purpose is to assess the genetic status of 3 day-old embryos. PGD offers thus to couples « at-risk » of a genetic disorder an earlier option to prenatal diagnosis (PND). At the beginning, PGD’s indications, patients and law were very closed to PND, but PGD specificities are gradually raising. Particularly, indications vary considerably in countries where the absence of law authorizes all the practices. Some of these applications are moreover raising serious ethical issues. Even in France, where this activity is particularly supervised, the recent modification to the law marks this evolution

Segregation of mtDNA Throughout Human Embryofetal Development: m.3243A > G as a Model System

Mitochondrial DNA (mtDNA) mutations cause a wide range of serious diseases with high transmission risk and maternal inheritance. Tissue heterogeneity of the heteroplasmy rate (“mutant load”) accounts for the wide phenotypic spectrum observed in carriers. Owing to the absence of therapy, couples at risk to transmit such disorders commonly ask for prenatal (PND) or preimplantation diagnosis (PGD). The lack of data regarding heteroplasmy distribution throughout intrauterine development, however, hampers the implementation of such procedures. We tracked the segregation of the m.3243A > G mutation (MT-TL1 gene) responsible for the MELAS syndrome in the developing embryo/fetus, using tissues and cells from eight carrier females, their 38 embryos and 12 fetuses. Mutant mtDNA segregation was found to be governed by random genetic drift, during oogenesis and somatic tissue development. The size of the bottleneck operating for m.3243A > G during oogenesis was shown to be individual-dependent. Comparison with data we achieved for the m.8993T > G mutation (MT-ATP6 gene), responsible for the NARP/Leigh syndrome, indicates that these mutations differentially influence mtDNA segregation during oogenesis, while their impact is similar in developing somatic tissues. These data have major consequences for PND and PGD procedures in mtDNA inherited disorders. Hum Mutat 32:116–125, 2011. © 2010 Wiley-Liss, Inc

Growth Development of French Children Born after In Vitro Maturation

International audienceBackgroundSeveral lines of evidence indicate that immature oocyte retrieval and subsequent in vitro maturation (IVM) without ovarian stimulation may be a reliable option in assisted reproductive technologies (ART). However, few outcome data are available for children born following this technique.ObjectiveWe assessed height and weight development of French children conceived after IVM.MethodsAll children conceived after IVM at Antoine Beclere Hospital (Clamart, France) and born between June 2003 and October 2008 (n = 38) were included in a prospective cohort study and compared with a control group of children conceived by ICSI without IVM, matched for maternal age, gestational age and singleton/twin pregnancies. Follow-up included clinical examination at one year and a questionnaire completed by parents when the children were two years old (97% follow-up rate).ResultsNo statistical differences between IVM and control groups were found for boys. Mean weight, height and head circumference at birth were significantly greater for IVM than for ICSI girls (3.236 kg vs 2.701 kg (p = 0.03); 49 cm vs 47 cm (p = 0.01) and 34 cm vs 33 cm (p = 0.04), respectively). At one year, IVM girls remained heavier (mean weight 10.2 kg vs 8.6 kg (p = 0.001)) and taller (76 cm vs 73 cm (p = 0.03)), and there was a two-point difference in BMI between the two groups of girls (18 vs 16 (p = 0.01)).ConclusionOur results in girls born after IVM should be interpreted with caution. It remains unclear whether the observed sexual dimorphism is due to IVM technology or to maternal characteristics such as underlying infertility in patients with polycystic ovary syndrome (PCOS). Further monitoring of the outcomes of these infants is required

Characteristics of Mothers and Pregnancies N = 68.

<p>Control : ICSI without IVM.</p

Characteristics of Infants at birth.

<p>Characteristics of Infants at birth.</p

Poor Correlations in the Levels of Pathogenic Mitochondrial DNA Mutations in Polar Bodies versus Oocytes and Blastomeres in Humans

Because the mtDNA amount remains stable in the early embryo until uterine implantation, early human development is completely dependent on the mtDNA pool of the mature oocyte. Both quantitative and qualitative mtDNA defects therefore may negatively impact oocyte competence or early embryonic development. However, nothing is known about segregation of mutant and wild-type mtDNA molecules during human meiosis. To investigate this point, we compared the mutant levels in 51 first polar bodies (PBs) and their counterpart (oocytes, blastomeres, or whole embryos), at risk of having (1) the “MELAS” m.3243A>G mutation in MT-TL1 (n = 30), (2) the “MERRF” m.8344A>G mutation in MT-TK (n = 15), and (3) the m.9185T>G mutation located in MT-ATP6 (n = 6). Seven out of 51 of the PBs were mutation free and had homoplasmic wild-type counterparts. In the heteroplasmic PBs, measurement of the mutant load was a rough estimate of the counterpart mutation level (R2 = 0.52), and high mutant-load differentials between the two populations were occasionally observed (ranging from –34% to +34%). The mutant-load differentials between the PB and its counterpart were higher in highly mutated PBs, suggestive of a selection process acting against highly mutated cells during gametogenesis or early embryonic development. Finally, individual discrepancies in mutant loads between PBs and their counterparts make PB-based preconception diagnosis unreliable for the prevention of mtDNA disorder transmission. Such differences were not observed in animal models, and they emphasize the need to conduct thorough studies on mtDNA segregation in humans