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[Effectiveness of a clinical test in the preselection of children with suspected fragile X syndrome].

BACKGROUND
Fragile X syndrome (FXS) is the most frequent hereditary cause of mental retardation. It can be diagnosed by molecular genetic techniques, but clinical suspicion is made less likely by it variable expression.


OBJECTIVE
To assess the effectiveness of a six-item checklist in the preselection of children who are candidates for FXS genetic study.


MATERIAL AND METHODS
We studied 70 male patients aged between 2 and 10 years with mental retardation of unknown cause. In all patients a checklist with six clinical criteria (mental retardation, history of familial mental retardation, long face, large ears, autistic-like behaviour, and attention deficit disorder with hyperactivity) measured from 0-2 points was applied and molecular genetic studies using polymerase chain reaction and Southern-blot were performed.


RESULTS
In 14 of the 70 children (20%) molecular study confirmed full mutation (200 CGG repeats). A score of six points in the test had the greatest discriminatory power and was reached by 14 patients (100%) with mutation, but only by 2of 56patients (3.5%) without mutation. The most accurate diagnostic model was the association of mental retardation, attention deficit disorder with hyperactivity, large ears and a history of familial mental retardation followed by long face and autistic-like behaviour.


CONCLUSIONS
The six-item checklist improved the preselection of children with suspicion of FXS, which was later confirmed by molecular genetic techniques.