Modèle géométrique de l'œuf de Ver à soie

Résumé L'uf de ver à soie qui se prête à de nombreuses recherches génétiques et physiologiques a été assimilé à un volume géométrique simple afin qu'on puisse calculer aisément l'aire de sa surface totale et son volume. On a d'abord cherché à justifier le modèle géométrique proposé grâce à une étude expérimentale et statistique. On a ensuite établi les formules mathématiques utiles. Enfin on a discuté de l'approximation donnée par ces formules et de leur signification biologique.

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Summary The egg of the silkworm which permits a lot of genetical and physiological researches has been assimilated to a simple geometric volume, so that the area of its total surface and its volume might be easily calculated. First we have tried to justify the geometrical model which is proposed by means of an experimental and statistical study. We have then demonstrated the useful mathematical formulas. Finally we have discussed the approximation given by these formulas and their biological significance.

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Zusammenfassung Das Seidenraupenei, das viele genetische und physiologische Forschungen ermöglicht, hat man mit einem einfachen geometrischen Modell verglichen, um seine ganze Fläche und sein Volumen leicht rechnen zu können. Zuerst hat man versucht, das vorgeschlagene geometrische Modell dank einer experimentalen und statistischen Arbeit zu rechtfertigen. Dann sind die nötigen mathematischen Formeln festgesetzt worden. Zuletzt hat man die durch diese Formeln gegebenen Annäherungen und ihre biologischen Bedeutung erörtert.

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Avec la collaboration technique de Mme.Donas     

La gangrène des organes génitaux externes de I’homme: Facteurs de risque et de pronostic

The objective of this study, based on 20 cases of necrotizing fasciitis of the male genitalia, is to identify the risk factors and prognostic factors of this disease. Most cases of necrotizing fasciitis of the male genitalia occurred in elderly men with a poor socio-economic level including 9 diabetics. There was no identifiable cause in 8 cases (Fournier’s gangrene). All patients underwent surgical excision and systematic antibiotic therapy. This series comprised 5 deaths (25%) in patients over the age of 69 years with extensive lesions and a very poor general state on admission. The outcome of survivors was favourable after a prolonged hospital stay (mean stay: 1 month). The clinical context therefore appears to play an essential role in the development of this disease and its subsequent prognosis, which could be improved by rapid and appropriate prevention and treatment.     

Les gangrènes des organes génitaux externes: à propos de 102 cas

Objectives

To describe the epidemiological, clinical, biological and therapeutic features of Fournier’s gangrene and identify the prognostic factors.

Patients and methods

We conducted a retrospective study on 102 cases of Fournier’s gangrene treated at the urology department of the university teaching hospital Aristide- Le-Dantec (Dakar) between January 2001 and December 2007.

Results

The mean age of the patients was 50.0 ± 15.7 years (range: 20–93 years). The mean duration of hospital stay was 8.0 ± 7.1 days (range: 1–33 days). The lesions were located on the scrotum in 61.7% of cases, on the scrotum and penis in 17.6% of cases and on the penis alone in 3.9% of the cases. Perineal involvement was found in 14.7% of the cases. No etiologic factors (idiopathic) were found in 26 cases (25.5%) and 70 patients (68.6%) had Fournier’s gangrene secondary to urethral stricture. The most common predisposing factors were diabetes mellitus (13.7%), hypertension (5.9%), and renal failure (5.9%). Biological examination revealed that 79.4% of patients had a leukocytosis higher than 12,000/ml and the mean rate of haemoglobin was 9.8 ± 2.8 g/dl (range: 3.3–13.9 g/dl). The most common antibiotherapy associated a third generation cephalosporin, aminoside and metronidazole (46.1%). Twenty-one patients (20.6%) underwent extensive debridement only and eighty-one (79.4%) underwent extensive debridement and cystostomy. The death rate was 15.7%. Among the patients whose Fournier’s gangrene was idiopathic or secondary to urethral stricture, the statistically significant factors for a poor outcome were age, the secondary character of the gangrene, the extent of the lesions, and association with diabetes mellitus and/or hypertension.

Conclusion

Fournier’s gangrene is still a frequent and lethal disease. Its good management requires a multidisciplinary approach.     

Théorie de la cible: Un modèle markovien pour l'évolution génétique d'une mutation latente

Résumé Chez les individus d'une mÊme espèce, un caractère héréditaire est supposé associé à une cible constituée de plusieurs particules, indépendantes entre elles, et susceptibles de se présenter sous diverses formes. Le phénotype dépend de la répartition de ces différentes formes dans la cible. A la division cellulaire correspond un certain mode de division de la cible, permettant la transmission des particules d'une génération à l'autre, et induisant des règles d'apparition des divers phénotypes. Le problème de la détermination du nombre des particules constituant la cible est examiné ici, et une solution est exposée. Cette solution tient compte à la fois des aspects mathématiques (étude théorique du processus), expérimentaux (observation de l'évolution génétique d'une mutation provoquée par un agent mutagène) et numériques (une technique d'ajustements numériques complète avantageusement l'étude théorique).

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Summary A hereditary character in individuals of the same species is envisaged as belonging to a target made up of several mutually independent particles, which can be manifested in diverse forms. The phenotype depends on the distribution of the different forms in the target. Cell fission then corresponds to a certain mode of division of the target, permitting particle transmission between generations. In this way the rules for appearance of various phenotypes are determined. The problem of determining the number of particles constituting a target is examined and a solution is given. This solution takes into account simultaneously three factors: a) mathematical (theoretical study of the process), b) experimental (observation of the genetic evolution of an artificially induced mutation) and c) numerical (a numerical fitting technique complements the theoretical study).

     

Structures génétiques comparées de trois espèces de rongeurs africains du genre Mastomys au Sénégal

Résumé Une analyse par électrophorèse des protéines à 20 locus a été réalisée sur trois espèces du genre Mastomys au Sénégal. Malgré l'absence de locus diagnostique, une approche multivariée par analyses factorielles (AFC et AFD) permet néanmoins de reconnaître de façon sûre une des espèces en présence (M. cf. natalensis, 100% d'individus bien classés par l'AFD) et d'attribuer correctement les individus des deux autres espèces (M. erythroleucus et M. huberti) dans 92% et 77% des cas respectivement. Bien qu'écologiquement nettement différenciées, ces deux dernières espèces apparaissent très proches génétiquement (D_Nei=0,12) et montrent par ailleurs de hétérozygoties très elevées. Les faibles distances génétiques entre les trois espèces contrastent avec la forte différenciation chromosomique observée par ailleurs. Chez M. erythroleucus et M. huberti, les distances génétiques observées entre populations continentales ne sont pas corrélées avec les distances géographiques alors que les populations insulaires présentent une nette baisse de variabilité, en relation probable avec leur isolement géographique important. Par ailleurs, chez M. huberti, plusieurs populations s'écartent fortement de la panmixie. Ces tensions génétiques pourraient résulter de phénomènes d'introgression avec M. erythroleucus.

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Compared genetic structures of three species of African rodents of the genus Mastomys from Senegal. A protein electrophoresis analysis at 20 loci was performed on three species of the genus Mastomys from Senegal. Although no diagnostic locus was found between the three species, they can be readily recognized by multivariate analysis (100% of the M. cf. natalensis, 92% of the M. erythroleucus and 77% of the M. huberti individuals could be correctly classified by discriminant analysis). Although ecologically quite clearly differentiated, M. erythroleucus and M. huberti were found to be genetically very close (D_Nei=0.12) and display very high heterozygosities. On the whole, the small genetic distances between the three species contrast with the high chromosomal differentiation that has been reported in another study. In M. erythroleucus and M. huberti, genetic distances between mainland populations are not correlated with geographic distances, whereas insular populations show an important decrease of variability probably linked with their geographic isolation. In M. huberti, some populations show a strong departure from panmictic equilibrium: these genetical tensions could result from introgression phenomena with M. erythroleucus.

     

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.