This study utilized the Autism Diagnostic Interview-Revised (Rutter et al., 2003) to examine diagnostic profiles and longitudinal change in autism symptoms for a group of children and adolescents with Fragile X syndrome with and without autism. FXS is the most common inherited cause of intellectual disability. Prevalence rates of autism in FXS may be as high as 50%, with many individuals displaying behaviors that are characteristic of autism, including eye gaze avoidance, repetitive behaviors and language delay. Previous studies have reported that individuals with comorbid FXS and autism are more impaired cognitively than individuals with FXS only, making it important to clarify the extent to which cognitive delay contributes to profiles of autistic behavior in FXS.
Objectives:
- To identify diagnostic and current symptoms of autism that distinguish participants with FXS-only from those with comorbid FXS and autism.
- To examine change over time in symptoms of autism within each diagnostic group.
- To identify diagnostic symptoms of autism that best predict group membership.
Methods:
Participants (N=51, 36 males) had a confirmed diagnosis of FXS and ranged in age from 10- to 16-years (M = 13-years, SD = 1.75). Participants were classified as having autism if they met the diagnostic cutoff scores for all domains of the ADI-R including age of onset, resulting in two subgroups: FXS-only (n = 26; 13 females) and FXS+AUT (n = 24; 2 females). The Brief IQ Screener of the Leiter-R (Roid & Miller, 1997) provided a measure of nonverbal IQ.
Results:
RQ1: After controlling for nonverbal IQ, significant between-group differences for lifetime and current symptoms of autism were not detected for the Reciprocal Social Interaction (RSI) domain of the ADI-R, but were revealed for both the Communication (COM) and Restricted Interests/Repetitive Behaviors (RRB) domains.
RQ2: On average, severity of autism symptoms improved over time for all participants, with the least improvement noted for behaviors in the RRB domain.
RQ3: In the RSI domain, group play with peers, nonverbal IQ, and social smiling discriminated significantly between the groups and correctly classified over 80% of participants. In the COM domain, stereotyped utterances/delayed echolalia, pointing to express interest, nodding, and nonverbal IQ discriminated significantly between the groups and correctly classified over 90% of participants. In the RRB domain, repetitive object use, circumscribed interests, and verbal rituals discriminated significantly between the groups and correctly classified over 70% of participants.
Conclusions:
Deficits in social reciprocity are considered to reflect the essential and defining feature of idiopathic autism. Lack of significant between-group differences for either algorithm or current items within the RSI domain suggests that autism symptoms in FXS may not reflect the same underlying mechanism as in idiopathic autism, but may reflect cognitive impairments that influence an individual’s ability to share enjoyment and interest with a social partner. Symptoms of autism improved over time for participants regardless of autism status with less improvement noted for the RRB domain. Nonverbal IQ added to group separation for the RSI and COM domains, but not for the RRB domain.