The fragile X syndrome

The currently available data concerning the fragile X syndrome are reviewed in this paper. The topics discussed are: (1) the phenotype of the mutation (including appearance, behavioural changes and mental retardation) and its cytogenetic features, (2) examples and hypotheses of atypical inheritance (genetic anticipation, Sherman paradox and X-inactivation-dependent mechanism giving rise tn this disease), (3) molecular studies (the expansion of the CGG repeat as the cause of the instability of the fragile X chromosome), (4) the FMR1 gene- its possible role, expression and proteins and (5) diagnosis and tests of the fragile X syndrome.