Autism symptom severity change was evaluated during early childhood in 125 children diagnosed with autism spectrum disorder (ASD). Children were assessed at approximately 3 and 6 years of age for autism symptom severity, IQ and adaptive functioning. Each child was assigned a change score, representing the difference between ADOS Calibrated Severity Scores (CSS) at the two ages. A Decreased Severity Group (28.8%) decreased by 2 or more points; a Stable Severity Group (54.4%) changed by 1 point or less; and an Increased Severity Group (16.8%) increased by 2 or more points. Girls tended to decrease in severity more than boys and increase in severity less than boys. There was no clear relationship between intervention history and membership in the groups.

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An individual's autism symptom severity level can change across childhood. The prevalence and direction of change, however, are still not well understood. Nor are the characteristics of children that experience change. Symptom severity trajectories were evaluated from early to middle childhood (approximately ages 3-11) for 182 autistic children. Symptom severity change was evaluated using individual change scores and the Reliable Change Index. Fifty-one percent of participants experienced symptom severity change: 27% of children decreased in severity, 24% increased and 49% were stable. Symptom severity decreases were more common during early childhood. Severity increases occurred at both early and middle childhood but increase in social affect severity was especially prominent during middle childhood. Most children experienced significant change during only one period and remained stable during the other. Girls decreased more and increased less in symptom severity than boys. Children that increased in severity decreased in adaptive functioning across childhood. Exploratory analyses indicated that a decrease in severity was associated with higher parental education level and older parental age at the time of the child's birth. Conversely, increase in autism severity was associated with lower parental education level and younger parental age at the child's birth. These findings extend recent observations that symptom severity change is more likely than previously appreciated. An understanding of the role of both biological and sociodemographic factors in determining a child's symptom trajectory may factor into future decisions on allocation and type of interventions distributed to young autistic children.Lay Summary: We studied whether a child's autism severity changed from initial diagnosis until middle childhood (ages 3-11). We found that 27% of the children decreased in severity, 24% increased and the rest stayed the same. Symptom severity decreases were more common during early childhood while severity increases were more prominent during middle childhood. We also found that girls were more likely to decrease than boys. Whether a child decreased or increased is related, in part, to parental characteristics.

One of the most universally accepted facts about autism is that it is heterogenous. Individuals diagnosed with autism spectrum disorder have a wide range of behavioral presentations and a variety of co-occurring medical and mental health conditions. The identification of more homogenous subgroups is likely to lead to a better understanding of etiologies as well as more targeted interventions and treatments. In 2006, we initiated the UC Davis MIND Institute Autism Phenome Project (APP) with the overarching goal of identifying clinically meaningful subtypes of autism. This ongoing longitudinal multidisciplinary study now includes over 400 children and involves comprehensive medical, behavioral, and neuroimaging assessments from early childhood through adolescence (2–19 years of age). We have employed several strategies to identify sub-populations within autistic individuals: subgrouping by neural, biological, behavioral or clinical characteristics as well as by developmental trajectories. In this Mini Review, we summarize findings to date from the APP cohort and describe progress made toward identifying meaningful subgroups of autism.

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