Techniques de recherche des polymorphismes génétiques

Sequencing the human genome has allowed the discovery of millions of DNA sequence variants. Sequence variations in human DNA are mainly present asSingle Nucleotide Polymorphisms (SNPs); this common form of variation is found about once every 1,000 bases in the human genome and 1.8 million SNPs have now been identified and located. The accessibility of databases of SNPs opens the possibility of studying the influence of these polymorphisms on disease risks as well as on drug responses. Numerous approaches have been set up for the identification of SNPs. In this review we describe the main techniques used for the identification of these polymorphisms. They rely on two major consequences of sequence variations: the apparition or the disappearance of restriction enzyme sites or the alteration of DNA strand hybridization due to the presence of a mismatch. Southern blotting and restriction endonucleases have allowed the development of the technique ofrestriction fragment length polymorphisms (RFLPs), now performed on PCR products. Several other approaches such as denaturing high-performance liquid chromatography or real-time PCR can detect allele differences upon re-hybridization and heteroduplex formation. However, DNA sequencing remains the obligate step for the positive identification of known or unknown SNPs. At last, the development of high-throughput methods allows a large increase in the rate of discovery of SNPs likely.     

Un estimateur de distributions ajusté pour une aide à la décision de la neutralité génétique des populations

The estimate of the neutrality of a population is often made from a single measurement based on simulations of random patterns. Disputed cases pose a problem regarding the decision-making about the neutrality of the study population. We propose in this paper to provide assistance to the decision of this problem by coupling a genetically neutral populations simulator to a fast adjusted non-parametric estimator of simulated distributions. The choice of the Epanechnikov kernel for the non-parametric method of estimating the kernel allows an analytical approach of the optimal bandwidth, which leads to an improvement in the complexity and therefore a gain in computing time. The fast and reliable estimation of simulated distributions allows to assess the credibility of the decisions about the neutrality of these populations. These results are illustrated by two Tunisian populations whose neutrality is not genetically determined.     

Conséquences de la chimiothérapie anticancéreuse sur la fertilité de la femme

Sterility is a potential toxic effect of chemotherapy. This risk is well established for alkylating agents, but is less clearly defined for anthracyclines, methotrexate and fluorouracil and poorly defined for alkaloids, platinum, etoposide and taxanes. The main predictive factors for ovarian toxicity are the additive effect of cytotoxic drugs, the cumulative dose of each drug and the patient’s age. This effect of chemotherapy is evaluated on menstrual cycles, hormonal assays and the number of pregnancies observed in patient cohorts. Chemotherapy induces destruction of oocytes and granulosa cells. In mice, it has been shown that adriamycin may induce oocyte apoptosis, which can be prevented by modulation of cycle cell signalling (dysregulation of Bax gene or, on the contrary, expression of its antagonist gene Bcl-2 or inhibition of apoptosis with sphingosine-1-phosphate or caspase inhibitors). Clinical data in the literature are usually based on retrospective studies and are somewhat confused: global fertility after MOPP chemotherapy for Hodgkin’s disease is about 20%, adjuvant chemotherapy with CMF, F(A)C or TAC for breast cancer induces amenorrhea in 50% to 70% of cases, PVB or BEP chemotherapy for ovarian germ cell tumors has little effect on fertility when the uterus and one ovary can be preserved, and the majority of women treated with methotrexate, actinomycin D or various combinations for persistent trophoblastic disease remain fertile. Preservation of fertility is a major goal for cancer patients receiving chemotherapy: in vitro fertilization could preserve the couple’s fertility, but is usually not feasible as it would delay initiation of chemotherapy until after stimulation of ovulation; oocyte or ovarian tissue cryopreservation is at the stage of research; oral contraceptives have not been demonstrated to be effective to preserve ovarian function; gonadotropin releasing hormone (GnRH) agonists prevent cyclophosphamide toxicity in rat and monkey ovaries, and a few pilot clinical studies suggest that chemotherapy-induced amenorrhea could be prevented by administration of GnRH analogues simultaneously to chemotherapy, but randomised studies are necessary.