Le syndrome de kallmann de morsier aspect génétique

Kallmann syndrome (KS) is a rare, heterogeneous disorder consisting of congenital hypogonadotropic hypogonadism, associated with anosmia (or hyposmia) and other clinical manifestations such as mirror movements, and renal, urological and neurosensory disorders. The presence of anosmia with micropenis in boys is suggestive of the diagnostic of KS. In KS, the GnRH neurons do not migrate correctly from the olfactory placode to the hypothalamus during development and olfactory bulbs also fail to form, leading to anosmia. Mutations in KAL1 which encodes Anosmin-1, are responsible for the X-linked form of KS. Anosmin-1 is normally expressed in the brain, facial mesenchyme, mesonephros and metanephros. It is required to promote migration of GnRH neurons into the hypothalamus. It also allows migration of olfactory neurons from the olfactory bulbs to the hypothalamus. The loss of function mutations in FGFR1 “fibroblast growth factor” were identified in 2003 as a cause of autosomal forms of this disease. An additional autosomal cause of Kallmann syndrome was recently identified by a mutation in the prokineticin receptor-2 gene (PROKR2) (KAL-3) and its ligand prokineticin 2 (PROK2) (KAL-4). Mutations in these genes induce various degrees of olfactory and reproductive dysfunction, but not the other symptoms seen in KAL-1 and KAL-2 forms of KS. Neuropilin2, which has an important role in migration of GnRH neurons, is a recent candidate gene for KS. The authors describe the genetic features and recent findings of KS, necessary to understand this disease.     

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.     

Sur le déterminisme de la formation de la grappe chez les abeilles

Conclusion Il existe une interattraction vraie chez les ouvrières d'Apis mellifica. Cette interattraction a pour point de dépárt un stimulus complexe pour une part de nature vibratoire et pour l'autre de nature olfactive.Le point de départ du stimulus olfactif se situe dans l'abdomen. Enfin pour que le stimulus soit perçu d'une manière efficace par l'abeille il faut que celle-çi soit intégrée à un groupe suffisamment nombreux.