A Longitudinal Study of Aggression in People with Autism and Other Neurodevelopmental Disabilities

Aggression is common in autism and neurodevelopmental disorders, but longitudinal research on aggression is lacking. We longitudinally tracked aggression in 254 individuals from toddlerhood to emerging adulthood. Our sample included participants with a range of cognitive abilities, with 39.9% classified as more-cognitively-abled (MCA; IQ ≥ 70) and 60.1% as less-cognitively-abled (LCA; IQ < 70). Aggression Composite scores were derived from data from the autism diagnostic observation schedule, autism diagnostic interview-revised, and child behavior checklist at ages 2, 9, and 18. Fifty-four percent, 69%, and 42% of the sample showed aggression in toddlerhood, school age, and emerging adulthood, respectively. LCA individuals had higher rates of aggression in school age (80%) and emerging adulthood (58%) compared to MCA individuals (48 and 22%, respectively). Longitudinal aggression profiles revealed distinct patterns of change over time: 31% displayed persistent aggression, 25% increased, 23% decreased, and 13% never displayed aggression. Higher autism symptoms, lower VIQ, NVIQ, and less-developed adaptive skills correlated with more aggression cross-sectionally. Nonverbal IQ and repetitive behaviors related to aggression longitudinally: people in decreasing or absent profiles had higher NVIQ and fewer RRBs than those with persistent or increasing profiles. Participants with aggression at 9 were four times likelier to exhibit aggression at 18. Aggression is common in autism and NDDs, peaking around age 9, and declining in emerging adulthood. Patterns of change varied widely, with evidence that higher NVIQ and fewer RRBs may be protective. Findings have implications for clinical practices, highlighting important developmental periods and high-risk subgroups.