[A study of the fragile X syndrome among the employees of the Spanish National Telephone Company]. / Estudio del síndrome X-frágil en la población de la compañía telefónica de España.

Our aim was to study the incidence rate of the X-fragile syndrome among the male employees throughout Spain and that of the physically handicapped dependants of those workers at the Spanish National Telephone Company (TESA), this last goal being to offer genetic counselling to their families. The method used was to check the census of the Telephone Company Handicapped Assistance Association (ATAM), which embraces all handicapped dependents of TESA employees. 386 mentally backward (IQ under 70) males were found. A cytogenic study was offered to all those cases of unknown etiology. A total of 49 cases (12.7%) without any data to lead us into thinking of other etiological factors refused to take part. Molecular genetic studies were carried out on families with male members diagnosed as having X-fragile syndrome. The results were as follows: the total number of patients suffering with this syndrome was eleven. The incidence rates of X-fragile syndrome in the group studied was 14.3/386 (3.7% of mentally backward males). Molecular genetics was more sensitive than cytogenetics in diagnosing the state of mother and sister carriers.

Fragile X syndrome with extra microchromosome.

A mentally retarded male with Martin-Bell syndrome, who has an extra microchromosome and is fra X negative in cytogenetic study is reported. Because of its small size, the origin of the microchromosome could not be determined. Two other affected males in this family (a cousin and a nephew of the proband) were fragile X positive, 24% and 26%, respectively. Cytogenetic studies and DNA analysis with the probe St B 12.3 were performed on several members of the family. The proband and the two other affected males showed a similar full mutation on the molecular study. This study emphasizes the importance of molecular analysis in the diagnosis of fragile X syndrome, particularly when cytogenetic studies demonstrate fra X negative in individuals in families likely to have X-linked mental retardation.