Summary: New research from the UC Davis MIND Institute finds that up to 30% of children diagnosed with autism show reduced symptom severity between ages three and six. Some children even no longer met diagnostic criteria by age six. The study also reports that girls on the autism spectrum are more likely than boys to experience a larger reduction in symptom severity and are less likely to show increased severity during early childhood.
Source: UC Davis
Girls with autism tend to show greater reductions and smaller increases in symptom severity during early childhood than boys, according to a UC Davis MIND Institute study.
Early childhood is a time of rapid brain development and learning, and it is also when most autism diagnoses are first made and when early intervention can have the greatest impact. In the United States, about 1 in 54 children has been identified with autism spectrum disorder (ASD), and males are diagnosed at roughly four times the rate of females.
Past studies produced mixed findings about how autism symptom severity changes over childhood, and many assumed that severity at the time of diagnosis remains relatively stable across the lifespan. The new MIND Institute study, published May 14 in the Journal of Autism and Developmental Disorders, tracked changes in autism symptom severity during early childhood and explored factors associated with those changes.
The study analyzed 125 children (89 boys and 36 girls) enrolled in the Autism Phenome Project (APP), a longitudinal research program at the MIND Institute. Participants were assessed at approximately age three and again around age six and received community-based autism interventions during the study period.
To measure symptom severity, researchers used the ADOS Calibrated Severity Score (CSS), a 10-point scale derived from the Autism Diagnostic Observation Schedule (ADOS), recognized as a gold-standard diagnostic tool in autism research. Each child’s symptom change score equaled the difference between their ADOS CSS at age six and at age three. A change of two or more points was treated as a meaningful change in severity.
Patterns of change in symptom severity and optimal outcome
Participants were grouped by change score into a Decreased Severity Group (28.8%), a Stable Severity Group (54.4%), and an Increased Severity Group (16.8%). One important takeaway is that autism symptom severity can and does change during early childhood—improvement is possible.
“Nearly 30% of children in this sample had less severe autism symptoms at age six than at age three,” said David Amaral, distinguished professor of psychiatry and behavioral sciences, MIND Institute faculty member, and the study’s senior author. “In some cases, children no longer met criteria for an autism diagnosis by age six.”
Amaral added that a separate subset of children showed increasing severity. “At present, we do not have reliable clinical predictors that identify which children will improve and which will experience greater symptom severity and require different supports,” he said.
In the study, seven participants (four girls and three boys) had ADOS CSS scores below the ASD cutoff at age six, suggesting a potential “optimal outcome” in which a prior ASD diagnosis is no longer met due to loss of observable symptoms. Children who experienced decreasing symptom severity also demonstrated stronger adaptive skills across multiple domains than children in the stable or increased severity groups.
Sex differences, camouflaging, and coping strategies
The study found notable differences between girls and boys in symptom trajectory. Girls tended to show greater reductions in severity and smaller increases compared with boys. One hypothesized explanation is that girls may be more likely to engage in social camouflaging—masking or compensating for autism-related social differences in everyday interactions.
“We observed that girls decreased in severity more than boys and increased in severity less than boys during early childhood,” said Einat Waizbard-Bartov, a graduate researcher at the MIND Institute and the paper’s first author. “Camouflaging is a coping behavior seen more often in females with ASD across age ranges and may account for some of this difference. We plan to investigate this possibility in future work.”
IQ, initial severity, and symptom change
The researchers also examined relationships between cognitive ability and symptom trajectories. Higher IQ was associated with greater likelihood of symptom reduction: as IQ scores increased from age three to age six, symptom severity tended to decrease.
Unexpectedly, the group of children whose symptoms increased by age six had, on average, lower ADOS severity at age three and less variability in their early severity scores than the other groups. The study did not find a clear relationship between the type or intensity of interventions recorded and group membership.
These findings raise important questions for future research, including how IQ, initial symptom levels, and characteristics of early intervention interact to influence symptom change during the preschool years.
Funding and authorship
This research was supported by grants from the National Institutes of Health (NIH) and by an Autism Center of Excellence award from the National Institute of Child Health and Human Development (NICHD). Additional support came from the MIND Institute Intellectual and Developmental Disabilities Research Center and the Simons Foundation.
Other contributors include Emilio Ferrer from the UC Davis Department of Psychology, and Brianna Heath, Gregory S. Young, Sally Rogers, Christine Wu Nordahl, and Marjorie Solomon from the UC Davis Department of Psychiatry and Behavioral Sciences.
About the published study
Article: “Trajectories of Autism Symptom Severity Change during Early Childhood” by Waizbard-Bartov et al., Journal of Autism and Developmental Disorders. The research evaluates ADOS-calibrated severity change between ages three and six in 125 children and reports that nearly 29% decreased by two or more ADOS CSS points, 54.4% remained essentially stable, and about 17% increased by two or more points. Girls were more likely than boys to show reductions in severity.
Contact
Media contact listed by UC Davis: Nadine A. Yehya – UC Davis.
Note
The findings highlight the variability of autism symptom trajectories in early childhood and underscore the need for further research to identify predictors of improvement and to tailor early interventions that best support each child’s developmental path.