Seven families with X-linked mental retardation (MR) have been studied clinically and cytogenetically. All affected males in six of the families were found to have a fragile site on Xq in a number of their peripheral lymphocytes. The fragile site was not seen in any of the affected males in the seventh family. The affected males in the six families with the fragile X had a syndrome characterized by a variable degree of MR, macro-orchidism, a characteristic repetitive, jocular speech, normal body proportions, and large jaws and ears. The fragile X chromosome could only be detected in a proportion of female carriers and its frequency in females was found to be correlated with their mental status to be inversely correlated with their age.

X-linked mental retardation: A study of 7 families

In the present report we summarize our data on 144 obligate female carriers. The clinical and cytogenetic data are reviewed and discussed. In more than 30% of heterozygotes mental development is borderline to subnormal, and they may also present psychiatric disturbances of which psychotic behaviour is the most frequent. Partial phenotypic expression is present in 28% of the carriers, and is more frequent in the mentally subnormal. Repeated fragile X screening remains negative in more than 50% of the patients. This results in great difficulties in accurate genetic counseling of the individual female at risk. In all females with partial clinical expression fragile X screening is positive. Fragile X carriers have a high fertility. A fourfold increase in twinning is observed and this may be an indication of a disturbed cortico-hypothalamic-hypophyseal axis.

The female and the Fragile X. A study of 144 obligate female carriers

The present report summarizes the experience on the mar(X) syndrome in a total of 157 male patients (44 prepubertal and 113 postpubertal) ascertained through 83 index patients from 83 families under investigation. In one third of the families pedigree data were consistent with X-linked recessive inheritance. In the further two thirds of the families the presenting symptom was familial mental retardation with a mentally retarded mother, or mental subnormality with hyperkinetic behaviour in the male patient. No more than 60% of the adult males presented the typical clinical triad (mental retardation-long face-megalotestes). The most characteristic finding in the mar(X) boy is the psychological profile with severe hyperkinetism, hypersensitivity, handbiting and autistic features in some of them. In 4 of the 27 large mar(X) pedigrees strong evidence was present of a possible transmission of the mar(X) through normal males. The high incidence of mental subnormality in the female offspring of heterozygote carriers, and the relationship between mental status, phenotype, age and expression of the mar(X) in different culture conditions is discussed.

The fragile X syndrome. A study of 83 families.

5-Fluoro-2'-deoxyuridine (FUdR) was found to be highly effective in inducing the heritable fragile site on Xq28 associated with mental retardation. Lymphocytes from two affected males manifested the fragile site in 30 to 40% of the mitoses when grown in the presence of FUdR. This observation suggests that depletion of the dTMP pool via thymidylate synthetase inhibition is responsible for the expression of the heritable fragile site on Xq28.

https://jmg.bmj.com/content/jmedgenet/18/5/374.full.pdf

5-Fluoro-2'-deoxyuridine induction of the fragile site on Xq28 associated with X linked mental retardation.

A survey of the mentally retarded children with an IQ between 30 and 55 born in a 10-year period (1955-64) and now of school age was carried out in New South Wales. The number of propositi who had a similarly affected sib of the same sex was ascertained; 58 boys had a similarly affected brother(s) and 22 girls had a similarly affected sister(s). It is suggested that the excess of affected brothers represents X-linked forms of mental retardation. An estimate of prevalence rate was calculated from the brother pair excess and was found to be 0 74/ 1000 males. The calculated incidence of X-linked forms of mental retardation appeared to account for most of the male excess found in the survey and suggests that 1 in every 5 of the mentally retarded boys in the IQ range in this survey may be retarded on the basis ofgenes on the X chromosome.

X-linked mental retardation.

The satellited-X chromosome previously shown in lymphocyte culture to be associated with certain types of sex-linked mental retardation has, for the first time, been demonstrated in cultured skin fibroblasts and lymphocytes from two affected males and an obligate carrier female. These findings provide a basis for reliable diagnosis of female carriers and for the development of prenatal diagnosis.

Expression in fibroblast culture of the satellited-X chromosome associated with familial sex-linked mental retardation

Chromosomal, clinical, and psychological data are presented on members of six families with X-linked mental retardation. Affected males in three of these families express the fra(X)(q28) marker, while the retarded males in the other three do not. Similar variable physical and psychological charateristics, such as lop ears, large testes, and perseverative speech, are present in affected males in all six families. Preliminary analysis of the psychological data also shows that males with and without marker expression cannot be differentiated with certainty. On this basis we suggest that there is a type of X-linked mental retardation with many phenotypic features of marker-X mental retardation but without expression of the X chromosome fragile site.

Further delineation of X-linked mental retardation.

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Expression in fibroblast culture of the satellited-X chromosome associated with familial sex-linked mental retardation

Further delineation of X-linked mental retardation.