Prevalence and cumulative incidence of autism spectrum disorders and the patterns of co-occurring neurodevelopmental disorders in a total population sample of 5-year-old children

Mol Autism. 2020 May 14;11(1):35. doi: 10.1186/s13229-020-00342-5.


Backgrounds: Whether there is a true increase in autism spectrum disorder (ASD) frequency or not remains unclear. Additionally, the rates of co-existing neurodevelopmental disorders (NDD) in a total population sample has not been fully examined before. Therefore, using a total population sample in Japan, we aimed to estimate the prevalence and cumulative incidence of autism spectrum disorder (ASD) annually, to determine whether there is a true increase in ASD prevalence by estimating the cumulative incidence of ASD annually, and to examine the rates of co-existing neurodevelopmental disorders (NDD).

Method: In this cross-sectional sequential design study, all 5-year-old children in the catchment area underwent the screening annually from the year 2013-2016. Screen-positive children were invited to participate in a comprehensive assessment, including child and parent interview, behavioral observation, and cognitive and motor function testing. All cases were reviewed by a multidisciplinary research team.

Results: Caregivers of 3954 children returned the screening, among which 559 children underwent the assessment with 87 children receiving an ASD diagnosis. Adjusted ASD prevalence was 3.22% (95% confidence interval (CI) 2.66-3.76%). The male to female ratio of the crude prevalence was 2.2:1. The cumulative incidence of ASD up to 5 years of age for the total study years was 1.31% (95% CI 1.00-1.62%). A generalized linear model revealed no significant linear trends in 5-year cumulative incidence over the study years. Only 11.5% of children had ASD alone; the remaining 88.5% were found to have at least one co-existing NDD.

Limitations: Modest sample size for a total population study.

Conclusions: Our findings demonstrate the stability of the 5-year cumulative incidence of ASD, implying no true rise in ASD incident cases over the 4-year study period in the study catchment area. High rates of co-existing NDDs reflect the importance of investigating broad developmental challenges in children with ASD.

Keywords: A total population study; Autism spectrum disorder; Co-existing neurodevelopmental disorders; Cumulative incidence; Prevalence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autism Spectrum Disorder / complications*
  • Autism Spectrum Disorder / diagnosis
  • Autism Spectrum Disorder / epidemiology*
  • Child, Preschool
  • Comorbidity
  • Cross-Sectional Studies
  • Female
  • Humans
  • Incidence
  • Infant
  • Japan / epidemiology
  • Male
  • Neurodevelopmental Disorders / complications*
  • Neurodevelopmental Disorders / diagnosis
  • Neurodevelopmental Disorders / epidemiology*
  • Population Surveillance
  • Prevalence
  • Risk Assessment
  • Risk Factors
  • Socioeconomic Factors