Syndrome de klinefelter et conseil génétique

Klinefelter’s syndrome is a common sex chromosomal aberration generally characterized by hypergonadotrophic hypogonadism and azoospermia. However, spermatogenesis impairment is variable and severe oligozoospermia can be found in some men, particularly those exhibiting a mosaic karyotype 47,XXY/ 46,XY. New reproductive technologies, such as intracytoplasmic sperm injection (ICSI), allow Klinefelter patients to have a progeny, even those who are azoospermic after testicular sperm recovery. The question therefore arises of whether or not there is a genetic risk for pregnancies from affected fathers. Sperm karyotyping, by in vitro penetration of zona-free hamster eggs or by fluorescence in-situ hybridization (FISH), is a method of choice for measuring aneuploidy rate in spermatozoa of patients carrying gonosomal abnormalities. A theoretical model would predict a high level of 24,XX and/or 24,XY disomic sperm cells in Klinefelter patients if 47,XXY spermatogonia were able to complete meiosis and achieve spermatogenesis. Interestingly, current observations show that the rate of abnormal spermatozoa in these patients is low, around 1–2%, which indicates that only 46,XY spermatogonia can produce mature sperm cells and that oligozoospermic Klinefelter patients probably carry a 47,XXY / 46,XY mosaicism, at least at the testicular level. However, this low but statistically significant level of disomic spermatozoa emphasizes the fact that their spermatogenesis occurs in a compromised environment which could increase the risk of meiotic errors. Therefore, the possible occurrence of autosomal aneuploidies in children born from Klinefelter fathers leads to the following recommendations: a) individual analysis by FISH of the sperm aneuploidy rate in each Klinefelter patient candidate for ICSI; b) proposal of fetal karyotyping after amniocentesis in pregnancies obtained by this technique.     

Le diagnostic génétique pré-implantatoire: premier bilan du groupe parisien

This paper reports the birth of the first fourteen infants conceived after preimplantation genetic diagnosis (PGD) in our unit. Fifty-nine couples were enrolled between January 2000 and July 2001. They had a total of 71 oocyte pick-up cycles. The collected oocytes were inseminated by intracytoplasmic sperm injection. The resulting embryos were biopsied on the third day of development and genetic analysis was performed on the same day. Most of the embryo transfers were carried out on the fourth day. The 71 oocyte pick-up cycles yielded 872 oocytes of which 731 were suitable for intacytoplasmic sperm injection. Among the 505 embryos obtained, 421 embryos were biopsied and genetic diagnosis was performed for 312 (74%) of them. 127 embryos were transferred during 58 transfer procedures. There were 18 biochemical and 12 ongoing (7 singles, 4 twins and 1 triple) pregnancies. Sixteen infants have been born and 2 are expected. PGD now constitutes an alternative for couples at risk of transmission of a serious and incurable genetic disease.     

Le cancer du testicule : facteurs de risque génétiques et environnementaux

The incidence of testicular cancer (TC) has a distinct geographic distribution but is increasing in most countries, including France. The most likely origin of TC is a lack of normal germ cell differentiation in the foetal testis. The maintained immature germ cells could proliferate after puberty to induce testicular tumor. Because of its frequent association with cryptorchidism and infertility, TC could be part of the testicular dysgenesis syndrome. The role of genetic factors is suggested by the frequency of familial TC cases, but no responsible gene has been clearly identified until now. Among the various studied genes, those regulating the KITLG/KIT pathway involved in primordial germ cell proliferation seem to play an important role. Studies made in immigrants and twins suggest the influence of environmental factors on the origin of TC. Hormonal deregulation occurring during prenatal life or puberty could facilitate the development of TC. However, the role of exogenous substances acting as endocrine disruptors has not been demonstrated yet.     

Le problème de la métamérie considérations générales

Summary The author deals with the meaning of metamerism. Two contrary points of view may serve to clear the problem. From the morphological point of view (Gegenbaur) probably outgrowth of the organism in longitudinal direction has led to the development of metameres. So the first (absolute) segmentation is due to a functional differentiation. In Phylogeny this segmentation has been maintained and the originally developed metameres remain the primary morphotic units of the organisms. Further specialising of function and organ-concentration destroyed the original absolute metamerism and only left a rest of the original.The functional point of view renounces an original absolute metamerism for the present moment. It only asks for the functional meaning of the segmentation in organisms, showing this segmentation. From the functional point of view it is possible that metamerism may be the morphological expression of quite different functional requirements and that in one organism the metamerism starts from another system of organs than in another.

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Zusammenfassung Es wird gefragt welche Bedeutung die Metamerie haben kann. Zur Erläuterung des Problems werden zwei extremen Betrachtungsweisen einander gegenübergestellt. Nach der morphologischen Betrachtungsweise (Gegenbaur) hat Wachstum der Organismen in die Länge wahrscheinlich zur Ausbildung der Metamerie geführt. Diese erste (absolute) Metamerie ist wahrscheinlich ein funktioneller Differenzierungsprozess gewesen.In der Phylogenese hat sich diese Metamerie behauptet und die ursprünglich entstandene Metamere sind die primären morphotischen Einheiten der Organismen geblieben. Weitergehende Funktionsspezialisierung und Organkonzentration hat die ursprüngliche absolute Metamerie vernichtet. Was davon übrig blieb sind die Reste der ursprünglichen.Die funktioneile Betrachtungsweise verzichtet vorläufig auf eine ursprüngliche absolute Metamerie. Sie fragt bloss nach der funktionellen Bedeutung, welche die Metamerie besitzt bei denjenigen Organismen, wo diese gefunden wird. Sie achtet es möglich, dass Metamerie der Ausdruck sein kann von ganz verschiedenen funktionellen Anforderungen und dass somit die Metamerie bei der einen Tiergruppe von einem ganz anderen Organsystem ausgeht wei bei einer anderen.