Heterogeneity in autism Identifying subgroups of autistic adults

Autism in adulthood is characterized by large differences between autistic people. These interindividual differences are often referred to as heterogeneity. As a result of this heterogeneity, autistic people often do not receive the support they need and prefer. Moreover, the heterogeneity within the autism spectrum, alongside the limited knowledge on the adulthood developmental trajectory, causes autistic adults to feel uncertain about what to expect as they reach older age. This PhD thesis aimed to bridge this gap, by advancing our knowledge on aging with autism, and the heterogeneity therein. We focused on the identification of subgroups, and their validity and potential utility for clinical practice. When data of autistic and non-autistic adults were combined, two subgroups were found: the first subgroup mainly included autistic adults, and the second mostly included non-autistic adults. To gain more insight into the heterogeneity within autism, the subgroup analysis was repeated for the autism group. Within the autism group, two subgroups were identified that were labeled as “Feelings of High Grip” and “Feelings of Low Grip”. These subgroups were (a) distinct on clinical outcomes (i.e., psychological difficulties, cognitive failures, and quality of life), (b) replicated in a separate sample, (c) stable over time, and (d) predictive of clinical outcomes when measured up to five years in time. The findings of this PhD thesis are important for the provision of tailored support in clinical practice, and for the understanding autistic adults and their loved ones may have of their future.