Molecular analysis of 53 fragile X families with the probe StB12.3.

Fifty-three pedigrees with the fragile X syndrome have been studied for amplification of the CGG repeat sequence adjacent to the CpG island in the FMR1 gene. Probe StB12.3 allowed direct detection of affected males, carrier females, normal transmitting males, as well as prenatal diagnosis. Comparison of our molecular data with our previous linkage data from 38 families indicates the effectiveness of direct DNA analysis. A total of 325 individuals were studied and no new mutation was found. All daughters of males with a premutation had a premutation. When the mother had a full mutation no children had a premutation. In premutated mothers, the size of the premutation seems to be a determining factor for the transition to the full mutation. All affected males had a full mutation or mosaicism and only 42% of the females with a full mutation were mentally impaired. Analysis of large families over 3 generations illustrated clearly the Sherman paradox. Furthermore, the analysis of these families is in reasonable agreement with the multiallelic model of Morton and Macpherson [Proc Natl Acad Sci USA 89:4215-4217, 1992]. Mosaic cases in the offspring of the mothers with a full mutation suggest a maternal germinal mosaicism. Then an abnormal methylation and a somatic heterogeneity established in very early steps of embryogenesis could explain these cases.

[Prenatal diagnosis of genetic diseases. Results of 57 early amniocenteses]. / Diagnostic prénatal des affections génétiques Bilan de 57 amniocentèses précoces

The authors report the results of anmiocenteses carried out early in 57 cases, in order to detect hereditary disorders in high risk pregnancies. They emphasize the necessity of prior genetic consultation and obstetric examination. Among the 57 cases, 53 had the examination carried out in order to seek a chromosome anomaly. The techniques of removal and culture are described. One pregnancy was interrupted, the foetus had a chromosome abnormality. The psychological aspect and the necessity of close cooperation between gynecologists and geneticians are discussed.

[What course should be adopted after the discovery of a gonosome anomaly in the fetal karyotype?]. / Quelle conduite adopter après la découverte d'une anomalie gonosomique du caryotype foetal?

An experience of three centers of genetic counselling (West France). The authors attempts to explain why in 9 cases the pregnancy was not terminated.

Prenatal diagnosis of a satellited non-acrocentric chromosome derived from a maternal translocation (10;13)(p13;p12) and review of literature.

We identified a familial balanced translocation involving chromosomes 10 and 13 through the finding of a satellited 10p chromosome in a fetus. The phenotype of two unbalanced products of the translocation resulting in pure monosomy 10p13 and trisomy 10p13 is described. This familial case and two of our unreported cases are discussed in the light of other prenatal observations with satellited non-acrocentric chromosomes reported in the literature.