This study yielded several important findings regarding the prevalence of, and changes in, autism symptoms in adolescents and adults with ASD. We found that, at these stages of life, there is a greater prevalence of impairments in nonverbal communication and social reciprocity than in verbal communication or repetitive behaviors and stereotyped interests, as shown on an item-level in . This pattern of findings lends support to the idea that impaired social reciprocity is both more central and more persistent than the other core symptoms of the autism behavioral phenotype (Mesibov et al., 1989
; Volkmar & Klin, 2005
Our findings also shed light on the nature of change, prospectively measured, in the core symptoms of autism. As in most prior research (reviewed in Seltzer et al., 2004
), we found evidence of both improvement and stability. Whereas the overall trend across measures was one of improvement, approximately half of the sample remained stable between Time 1 and Time 4 with respect to nonverbal communication impairments, impairments in social reciprocity, and all measures of maladaptive behaviors. Although worsening of symptoms was observed in only a small minority of sample members, identification of factors differentiating those whose symptoms and maladaptive behaviors worsened is warranted in future research.
Although there was heterogeneity in the distribution of change, every scale with significant mean change was in the direction of improvement. There was significant improvement for 19 of the 32 autism symptoms and seven of the eight maladaptive behaviors. Improvement was especially notable in the domain of repetitive behaviors and interests, with all items in this domain improving significantly during the study period. It is noteworthy that repetitive behaviors, which in early childhood tend to be a very prevalent feature of the behavioral phenotype of autism, were currently among the least prevalent while simultaneously being among the most likely to improve.
At first glance, this last finding might seem contrary to the finding by Piven et al. (1996)
that repetitive behaviors were less likely to improve when compared to social and communicative measures. However, Piven et al. were examining the likelihood of change between early childhood and adulthood. In contrast, our analyses examined change during a 4.5-year period within
adolescence and adulthood. The likelihood of improvement of maladaptive behaviors was greater among those who were age 31 and older at Time 1 as compared to those aged 10 through 21. Thus, it may be that the likelihood that certain sets of symptoms will improve may vary over the life course, with some symptoms being more likely to improve during childhood and others being more likely to improve during later developmental periods. This finding suggests a long-term pattern of phenotypic symptom decline in repetitive behaviors during adolescence and adulthood. It also is possible that this pattern of improvement reflects the cumulative effects of interventions and medications. Overall, our findings underscore the importance of using a life course perspective when considering questions of change and development among people with an autism spectrum disorder.
We predicted that the older cohorts would be more likely to improve between Time 1 and Time 4 than the adolescent cohort. This prediction was supported for all four maladaptive behavior scales, but not for autism symptoms. Thus, reduction in maladaptive behavior continues well into and may even accelerate in midlife for individuals with ASD, whereas autism symptoms appear to improve at a steady rate across different age cohorts. Whether or not a sample member had a diagnosis of mental retardation was the most robust predictor of change in both autism symptoms and maladaptive behaviors from Time 1 to Time 4, similar to what has been found in earlier stages of life. Those with mental retardation improved less than those without this comorbid diagnosis. Although in childhood, having better verbal skills is predictive of a good prognosis, in adolescence and adulthood it was only predictive of improvement in social reciprocity but none of the other outcomes. Males and females appeared to change to the same degree.
One limitation of this study was the relatively short period of time examined (4.5 years). It is possible that more gradual, but nonetheless clinically important, patterns of change could be captured by a longer study period. Another potential limitation was our reliance on parent-report data, which is generally seen as less desirable than direct observational measures. However, the ADI-R is not a self-administered instrument but rather is scored by trained interviewers based on parent responses to structured probes. It is currently recognized as the “gold standard” measure for evaluating autism symptoms (Filipek et al., 1999
), and prior research has established strong agreement between ADI-R ratings based on parent report and expert ratings based on direct clinical assessment (Lord et al., 1994
). Likewise, the SIB-R has been extensively validated in large samples and correspondence between parent and clinician ratings is strong (Bruininks et al., 1996
). It is also possible that the repeated interviews alone would lead parents to report improvement. However, we do not think this is the case. Items showed a heterogeneous pattern of change, with some items improving significantly (to varying degrees) and others remaining stable. If change was an artifact of self-report methods, we would expect more uniformity than was observed.
The study also had several strengths. First, it was based on a large community sample, thereby improving power while reducing the likelihood of referral bias common in clinic samples. Second, the study examined changes into adolescence and adulthood, two life stages that are underrepresented in the literature on autism. Third, the study extends our understanding of maladaptive behaviors in this population, which has received comparatively less attention in past research.
The results of this study also have important implications for intervention. Treatment models are much less widely available for adolescents and adults than for young children with autism. Yet, the present analyses as well as prior research indicate that symptoms and behaviors can improve across the life course. Over time, patterns of improvement represent the product of interactions among the ASD genotype, the ASD behavioral phenotype, and the environment, including the family environment, treatments, and interventions. Future research should explore the effects of interventions tailored to adolescents and adults with ASD and their families.
Finally, the tendency towards improvement among individuals with ASD should not be construed as a justification for scaling back the availability of interventions and services under the false assumption that this population’s impairments will spontaneously remit to a point where assistance and supervision is not required. To the contrary, despite the overall tendency towards improvement, the majority of individuals in our sample remain significantly impaired and dependent on the assistance of others for daily living. Therefore, our findings should give greater impetus to extending interventions and services for this population across the life course.