A deletion of 1.6 Kb proximal to the CGG repeat of the FMR1 gene causes fragile X-like psychological features.

In this report we present the results of psychological investigations in a family in which 11 individuals, 7 females and 4 males, have a deletion of 1.6 Kb proximal to the CGG repeat of the FMR1. All 4 males with the deletion and 2 of the female carriers show characteristics of the fragile X clinical and behavioural phenotype. The findings in the present family illustrate that the typical characteristics of the fragile X syndrome can be caused by other types of mutations involving the FMR1 than the highly expanded stretches of CGG repeats in the 5' noncoding region of the FMR1 gene, coinciding with abnormal methylation patterns in that area as present in the vast majority of individuals with the fragile X syndrome.