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[Fragile X syndrome and mental retardation].

INTRODUCTION
Fragile-X syndrome is characterized by the presence of a fragile site (gap) on Xq 27.3 and the transcriptional inhibition of a mRNA protein-binding gene called FMR-1. Neuropsychological features include cognitive impairment, attention deficit disorder with and without hyperactivity, and impairment of visuospatial functions, language and frontal executive functions. In the present paper, other cytogenetic and phenotype characteristics, associate disorders, neurological and neuroimaging studies are revised.


CLINICAL CASES
We describe two siblings that illustrate the pattern of neurocognitive and behavioural trends of the Fragile X syndrome, and sex differences.


DISCUSSION AND CONCLUSIONS
These two cases emphasize the need for performing a cytogenetic diagnostic in patients with mental retardation, of unknown etiology, and with a familiar history of mental retardation.