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A Danish Cohort Study

Hjördís Ósk Atladóttir, MB; Erik T. Parner, MSc(Stat), PhD; Diana Schendel, PhD; Søren Dalsgaard, MD, PhD; Per Hove Thomsen, DMSc; Poul Thorsen, MD, PhD

Arch Pediatr Adolesc Med. 2007;161(2):193-198.

Objectives  To examine trends in autism (autism spectrum disorder and childhood autism) in the context of 3 additional childhood neuropsychiatric disorders: hyperkinetic disorder, Tourette syndrome, and obsessive-compulsive disorder.

Design  Population-based cohort study.

Setting  Children were identified in the Danish Medical Birth Registry. Relevant outcomes were obtained via linkage with the Danish National Psychiatric Register, which included reported diagnoses through 2004 by psychiatrists using diagnostic criteria from the International Statistical Classification of Diseases, 10th Revision.

Participants  All children born in Denmark from 1990 through 1999, a total of 669 995 children.

Main Outcome Measures  Cumulative incidence proportion by age, stratified by year of birth, for each disorder.

Results  Statistically significant increases were found in cumulative incidence across specific birth years for autism spectrum disorder, childhood autism, hyperkinetic disorder, and Tourette syndrome. No significant change in cumulative incidence was observed for obsessive-compulsive disorder.

Conclusions  Recent increases in reported autism diagnoses might not be unique among childhood neuropsychiatric disorders and might be part of a more widespread epidemiologic phenomenon. The reasons for the observed common pattern of change in reported cumulative incidence could not be determined in this study, but the data underscore the growing awareness of and demand for services for children with neurodevelopmental disorders in general.

Author Affiliations: North Atlantic Neuro-Epidemiology Alliances at Department of Epidemiology (Drs Atladóttir, Parner, and Thorsen) and Department of Biostatistics (Drs Atladóttir and Parner), Institute of Public Health, University of Aarhus, Aarhus, Denmark; Centers for Disease Control and Prevention, Atlanta, Ga (Dr Schendel); and Psychiatric Hospital for Children and Adolescents, Aarhus University Hospital (Drs Dalsgaard and Thomsen).