Association of SRS Score with Other Phenotypic Variables In ADHD and ASD

Background:  Co-occurrence of Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism symptoms has previously been demonstrated in clinic- and population-based samples (Grzadzinski et al., 2010; Reiersen, Constantino, & Todd, 2008; Reiersen, Constantino, Volk, & Todd, 2007).  The Social Responsiveness Scale (SRS) has been previously used to measure autistic symptoms in children with ADHD and other psychiatric disorders(Grzadzinski et al., 2010; Reiersen et al., 2008; Reiersen et al., 2007; Towbin, Pradella, Gorrindo, Pine, & Leibenluft, 2005). In a population-based sample, SRS score was higher in combined type ADHD than in the inattentive subtype(Reiersen et al., 2007). Previous studies of autistic symptoms in ADHD samples have shown association of the SRS with parent-reported motor coordination problems (Reiersen et al., 2008)as well as co-occurring psychopathology, including oppositional behavior(Grzadzinski et al., 2010).

Objectives:  To investigate the association of SRS score with motor function, co-occurring psychopathology, and other phenotypic variables within clinically ascertained children and adolescents diagnosed with ADHD or Autism Spectrum Disorder (ASD).

Methods:  Subjects include 242 individuals recruited for participation in studies of ADHD or ASD (61 with ADHD, 74 with Autism, 107 control subjects with neither diagnosis).  The Social Responsiveness Scale was available as a measure of autistic traits in all subjects. Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R) data were available on ASD subjects. Several measures of motor function and co-occurring psychopathology were available on all subjects. We examined the mean and distribution of SRS scores in each subject group and investigated the association of SRS score with other phenotypic variables within each subject group.

Results:  Mean SRS scores were moderately elevated in ADHD and higher in ASD subjects, but similar between combined and inattentive ADHD subtypes. Within the ADHD and ASD groups, parent-rated SRS score was significantly associated with a parent-rated questionnaire-based measure of motor function (the Developmental Coordination Disorder Questionnaire), but not with several exam-based measures of motor function. Some subscales from a questionnaire-based measure of anxiety (the SCARED) were also significantly associated with SRS score. There appeared to be a slight distributional shift toward increased (more severe) SRS scores among subjects with ADHD or ASD who had an additional diagnosis of oppositional defiant disorder (ODD), but a statistically significant relationship between the categorical measure of ODD and the total SRS score was not found in either of the clinically affected groups.

Conclusions:  The findings are largely consistent with some previous studies suggesting association of parent-reported motor coordination problems and ODD symptoms with SRS score in children whose primary diagnosis is ADHD.  Mean SRS scores in the ADHD group were similar to those reported for inattentive ADHD in a previous sample.  The lack of ADHD subtype differences in mean SRS score may be due to differences in ascertainment method (i.e., clinical sample vs. population sample and efforts to obtain a relatively “pure” ADHD group without evidence of ASD).