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Secular changes in the symptom level of clinically diagnosed autism.

Journal article
Authors Olof Arvidsson
Christopher Gillberg
Paul Lichtenstein
Sebastian Lundström
Published in Journal of child psychology and psychiatry, and allied disciplines
Volume 59
Issue 7
Pages 744-751
ISSN 1469-7610
Publication year 2018
Published at Gillberg Neuropsychiatry Centre
Centre for Ethics, Law, and Mental Health
Pages 744-751
Language en
Keywords Neurodevelopmental disorders; autism spectrum disorders; prevalence
Subject categories Child and adolescent psychiatry


The prevalence of autism has been reported to have increased worldwide. A decrease over time in the number of autism symptoms required for a clinical autism diagnosis would partly help explain this increase. This study aimed to determine whether the symptom level of clinically diagnosed autism cases below age 13 had changed over time.Parents of Swedish 9-year old twins (n = 28,118) participated in a telephone survey, in which symptoms and dysfunction/suffering related to neurodevelopmental disorders [including autism, but also attention-deficit/hyperactivity disorder (ADHD), Developmental Coordination Disorder (DCD), and Learning Disabilities (LD)] in their children were assessed over a 10-year period. Survey data was merged with the National Patient Register containing clinically registered autism diagnoses (n = 271).In individuals who had been clinically diagnosed with autism before the age of 13, the symptom score for autism decreased on average 30% over more than a decade in birth cohorts 1992-2002. There was an average decrease of 50% in the autism symptom score from 2004 to 2014 in individuals who were diagnosed with autism at ages 7-12, but there was no decrease in those diagnosed at ages 0-6.Over time, considerably fewer autism symptoms seemed to be required for a clinical diagnosis of autism, at least for those diagnosed after the preschool years. The findings add support for the notion that the observed increase in autism diagnoses is, at least partly, the by-product of changes in clinical practice, and flag up the need for working in agreement with best practice guidelines.

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