Phenotypic Similarity Between XYY Syndrome and Autism Spectrum Disorder

Background: XYY syndrome is a sex chromosome condition in which a male receives an extra Y-chromosome. Since there are subtle physical or medical findings, XYY is often not detected unless genetic testing is conducted. Although research on the behavioral characteristics of individuals with XYY is in its infancy, there is emerging evidence that many boys with XYY exhibit behavioral profiles that share key characteristics with autism spectrum disorder (ASD).

Objectives: Because there is little known about the behavioral profiles of boys with XYY, our goal was to determine which behavioral characteristics best differentiated the XYY group from controls. Additionally, we were interested in evaluating behaviors suggestive of ASD in children with XYY to better understand the behavioral profiles of these children.

Methods: The Child Behavior Checklist 4-18 (CBCL; Achenbach, 1991) and the Social Communication Questionnaire (SCQ; Rutter, Bailey, & Lord) were administered to the parents of thirty-two XYY and thirty age-matched normal control participants. The average age was nine-years-old for both groups.

Results: Mean scores on all eight CBCL syndromes were significantly higher in the XYY group than the control group, with the largest effect sizes (ESs) on Social Problems (43%), Attention Problems (42%), and Aggressive Behavior (31%). To test which CBCL items differentiated the XYY group from the control group, we conducted a MANOVA on all 118 items and aggregated those that were significant into a XYY scale (34 items). This XYY scale had a larger ES than any other CBCL scale (ES = 53%). Finally, we compared the XYY group and the control group on an ASD scale derived from CBCL items by Ooi et al. (2010) in Singapore. Results indicated that the ASD scale actually had the overall largest ES (54%). To further investigate the presence of ASD symtomatology, we analyzed the results of the Social Communication Questionnaire. SCQ data were available for 29 XYY and 22 control participants. Results indicated that 14 children in the XYY group scored at or above the recommended cutoff of 15 whereas no children in the control group scored at or above the cutoff.

Conclusions: The existing research on the behavioral profiles of children with XYY is scarce. The existing stereotype of XYY is that these males are impulsive and aggressive; however, this study suggests that, in comparison to typically developing controls, they have significant social and attentional problems. Furthermore, the XYY boys, as a group, have many symptom characteristics similar to children with ASD. Implications of this study are that some of the treatments that are effective with higher functioning children with ASD – such as behavioral interventions, speech therapy, and social skills training – might be helpful for XYY youngsters as well.