[Can the behavioural phenotype of fragile X syndrome be attributed to mental retardation and to attention deficit hyperactivity disorder?].

INTRODUCTION Fragile X syndrome (FXS) reveals itself as dysmorphic stigmata, systemic manifestations, neurological symptoms and cognitive-behavioural manifestations. Mental retardation (MR) and attention deficit hyperactivity disorder (ADHD) nearly always appear as examples of this last case, but most patients also present a series of fairly common behavioural characteristics. The most characteristic types of conduct seen in FXS include: language problems, lack of attention, hyperactivity, anxiety, shyness, behavioural problems, stereotypical hand flapping, gaze aversion, obstinacy and aggressiveness. AIMS The purpose of this work is to determine which behavioural aspects of the syndrome are linked to the genetic specificity and are not, therefore, determined by MR and ADHD. PATIENTS AND METHODS Three groups of patients were compared: 30 children diagnosed as suffering from FXS, 30 children with MR caused by diverse aetiologies and 323 children diagnosed as suffering from ADHD. RESULTS It was found that there were no significant differences between the IQ and the age of the FXS and MR groups. To determine the behavioural characteristics of the three groups the parents of the patients answered Achenbach's CBCL/4-18 survey. CONCLUSIONS The results obtained show that certain types of conduct that are very typical of FXS are represented significantly more frequently in the FXS group than in the groups of patients with MR and ADHD. This behaviour includes: timidity, attachment to adults, shyness, repetition of certain actions over and over again, pronunciation and speech problems, fear of animals, situations or places, and concern for tidiness and cleanliness. These findings lend support to the idea that the behavioural phenotype of FXS is linked to the genetic disorder and is not, therefore, a consequence of MR or ADHD.