[Family studies in the fragile X syndrome].

A family study and detection of bearer individuals has been carried out in five families suffering from the fragile X syndrome by means of clinical and cytogenetical examination, as well as by DNA recombination techniques in one of them. In 14 males the X marker chromosome was found. In 45 females studied in order to find bearer features, 23 heterozygote individuals have been detected. Out of those 23 cases, 11 were fragile X positive and in the remaining 22 a previous risk of 25-50% was estimated. In this group we used the Bayes theorem considering as conditional probabilities to bear a healthy male and to be fragile negative and the risk of being a bearer person decreased in all the cases. The significance and difficulties of the genetical prevention in families suffering from this syndrome because of the great number of young female with risk at the reproductive age are debated. The DNA study with the St14 sound (DXS52 Locus) in a family was concordant with the cytogenetical studies. A possible recombination in an individual suffering from fixation, atypical phenotype and low percentage of the maker expression.