Autism in fragile X syndrome: a category mistake?
OBJECTIVE
Many investigators now routinely classify children with fragile X syndrome (FXS) according to whether or not they also meet diagnostic criteria for autism. To determine whether this classification is appropriate, we examined the profiles of autistic behaviors shown by boys and girls with FXS.


METHODS
Individuals with FXS, aged 5 to 25 years, were assessed on two established measures of autism, the Social Communication Questionnaire (SCQ) and the Autism Diagnostic Observation Schedule (ADOS).


RESULTS
We found that 35.1% of boys and 4.3% of girls with FXS scored in the "autism" category on both instruments. Analysis of the symptom profile indicated that both boys and girls with FXS showed lower rates of impairment on communication and reciprocal social interaction items than the reference autism samples on the measures. Furthermore, a regression model showed that IQ was significantly negatively associated with the SCQ total score in both boys and girls with FXS, when controlling for age, medication use, and FMRP levels.


CONCLUSIONS
These data suggest that there are significant differences in the profile of social and communicative symptomatology in FXS compared with individuals diagnosed with idiopathic autism. Given these differences, the implementation of standard autism interventions for individuals with FXS may not be optimal. Maintaining the conceptual distinction between FXS (an established biological disease) and idiopathic autism (a phenomenologically defined behavioral disorder) may also facilitate the development of more targeted and thus effective interventions for individuals with FXS in the future.
Hall
Scott S
SS
Center for Interdisciplinary Brain Sciences Research, Department of Psychiatry and Behavioral Sciences, 401 Quarry Road, Stanford University, Stanford, CA 94305-5795, USA. hallss@stanford.edu
Lightbody
Amy A
AA
Hirt
Melissa
M
Rezvani
Ava
A
Reiss
Allan L
AL
D000293:Adolescent; D057189:Checklist; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000145:classification* / Q000175:diagnosis* / Q000523:psychology; D002675:Child, Preschool; D003142:Communication; D015897:Comorbidity; D003937:Diagnosis, Differential; D005260:Female; D005600:Fragile X Syndrome / Q000145:classification* / Q000175:diagnosis* / Q000523:psychology; D006801:Humans; D007360:Intelligence; D008297:Male; D010552:Personality Assessment / Q000706:statistics & numerical data; D011594:Psychometrics; D012737:Sex Factors; D012919:Social Behavior; D013239:Stereotyped Behavior; D055815:Young Adult