Epidemiology of ASD in Preschool-age Children in Japan

*Manabu Saito, Yui Sakamoto and Ai Terui*

## **Abstract**

In recent years, it has been reported that the prevalence of autism spectrum disorder (ASD) is increasing, but there are few research reports in Asia equivalent to those in Europe and the United States. Since large-scale epidemiological studies of neurodevelopmental disorders (NDDs) have not been conducted in Japan, the delay in early detection is conspicuous compared to other countries. Therefore, we started epidemiological studies in a medium-sized city (Hirosaki City) in northern Japan from 2013 to elucidate the prevalence of ASD and have been conducting a 9-year community cohort survey. In 2020, we published an adjusted prevalence of ASD of 3.2% at the age of 5 years, no change in 4-year incidence, and comorbidity of ASD. Since then, we have focused on sleep problems at the age of 5 years and have been studying the estimation of the prevalence of sleep disorders and the relationship with neurological development disorders. In this chapter, in addition to our research results since 2013, we will introduce the screening and support system in the community in Japan.

**Keywords:** autism spectrum disorder, prevalence, preschooler, sleep problems, screening system

### **1. Introduction**

In epidemiological studies, the prevalence of autism spectrum disorder (ASD) has changed significantly over the last 20 years. A 2018 study by the Centers for Disease Control and Prevention (CDC) reported a prevalence of 2.30% (1 in 44 children) among children aged 8 years [1]. In 2008, the prevalence was 1 in 88 children [2], so the ADDM network reported that the prevalence of ASD has doubled in 10 years. Diagnostic criteria are American Psychiatric Association's the Diagnostic and Statistical Manual of Mental Disorders (DSM), Fourth Edition, Text Revision (DSM-IV-TR), 5th ed. (DSM-5), the World Health Organization's International Statistical Classification of Diseases and Related Health Problems (ICD), Ninth Revision (ICD-9) or Tenth Revision (ICD-10), indicating the importance of following the same criteria [3–6].

In Asia, a large-scale study by YS Kim et al. in 2011 reported the prevalence of ASD with similar diagnostic criteria, reporting 2.64% in children aged 7–11 years [7]. In Japan, there has been no large-scale epidemiological study by DSM criteria, and in 2020 we reported for the first time that the prevalence of 5-year-old ASD in the community was 3.22% [8].

In recent years, as the heterogeneous nature of brain and sensory functions in neurodevelopmental disorders (NDDs) has been clarified, it has been suggested that ASD symptoms can be improved by early intervention, and ASD has undergone a paradigm shift as a disorder in which neuroplasticity can be expected [9]. In addition, it has been reported that people with neurodevelopmental disorders often have complications such as depression, anxiety disorders, and conduct disorders [10, 11]. Many of these complications occur as secondary disorders of neurodevelopmental disorders (NDDs), and early detection of developmental characteristics and early intervention are considered important to prevent secondary disorders [12]. In this chapter, in addition to our research results since 2013, we will introduce the screening and support system in the community in Japan.

### **2. Epidemiology of ASD in preschool-age children in Japan**

#### **2.1 Infant health checkup system in Japan**

In Japan, the Maternal and Child Health Law requires municipalities to conduct health and development checkups for children aged 18 and 36 months [13]. At these checkups, public health nurses and pediatricians assess physical, motor, social, emotional, behavioral, verbal development, and general health (medical and dental). If these assessments are found to be abnormal, the public health nurse and/or pediatrician should refer the patient to a specialist for further evaluation, if necessary, and have the child's caregiver available for early intervention, such as speech therapy. Providing local resources where possible is encouraged (but not compulsory). According to a Ministry of Health, Labor, and Welfare report published in 2020, the 18-month health checkup rate in Japan was 95.2%, and the 36-month health checkup rate was 94.5% [14].

While the participation rate in infant health checkups is high and infant deaths are sufficiently prevented, the rate of finding prominent neurodevelopmental disorders in health checkups is extremely low at 0.2–1.3%. Therefore, in 2017, the government made recommendations for early detection of neurodevelopmental disorders in infant health checkups [15]. The number of children receiving special support after entering elementary school has tripled from 10 years ago [16]. There is a gap between the high need for support due to the awareness of neurodevelopmental disorders by guardians and caregivers and the low detection rate in the health checkup system.

#### **2.2 The Hirosaki five-year-old children developmental health check-up (HFC) study**

The Hirosaki Five-year-old Children Developmental Health Check-up (HFC) study was established in 2013 using a total population sample of 5-year-olds living in Hirosaki City, Japan. The rationale for this study is that, despite the high participation rate in these assessments, the data of children who screened positive for NDD at 18-month or 36-month health checkup or follow-up arose from concerns about the limited. There were also concerns about whether children who screened positive before the age of 5 years were subsequently evaluated and received appropriate services. This study, in collaboration with the University of California, San Francisco (UCSF), used HFC data from 2013 to 2016 to estimate the prevalence and 5-year cumulative incidence of ASD at the age of 5 years. We investigated patterns of comorbidity of NDDs in children with ASD, including hyperactivity disorder (ADHD), developmental coordination disorder (DCD), and intellectual disability (ID) [8].

Five-year-old Children Developmental Health Check-up was conducted annually between January 2013 and December 2016, and four cohorts were created. HFC was conducted in two stages and aimed to detect all children with NDD in the community. The primary screening was a series of questionnaires mailed by Hirosaki City to the parents and kindergarten or nursery school teachers of all 5-year-olds living in the city. The questionnaire used epidemiological information (children's gender, family composition, parental education, and employment history, etc.) and the following scales: Autism Spectrum Screening Questionnaire (ASSQ ), Strengths and Difficulties Questionnaire (SDQ ), ADHD Rating Scale-IV (ADHD-RS-IV), Developmental Coordination Disorder Questionnaire (DCDQ ), and Parenting Stress Index (PSI) [17]. The parent has completed all of the above questionnaires, and the teacher has completed SDQ. All of the above tools have been translated into Japanese, and their reliability and validity had previously been established [18–22].

In the second stage of evaluation, a comprehensive evaluation of NDDs in screen-positive children was performed at Hirosaki University Hospital. Caregivers of screen-positive children were invited to participate in a comprehensive evaluation. **Figure 1** is a flow chart of the screening and evaluation stages of HFC research.

At the comprehensive assessment, developmental history and concerns were collected using items derived from the Diagnostic Interview for Social and Communication Disorders (DISCO) [23]. The DISCO is a semi-structured interview schedule designed to collect information on development and behavior. It can be used to assist in identifying possible diagnostic categories, including ASDs and other developmental disorders affecting social interaction and communication.

#### **Figure 1.**

*Flow chart of the Hirosaki five-year-old developmental Checkup and assessment.*

Cognitive assessments were conducted by psychologists using the Japanese version of the Wechsler Intelligence Scale for Children, 4th edition (WISC-IV) [24] only for children who did not have an ID diagnosis before participating in the present study. Assessment of children's coordination skills was performed by trained occupational therapists and psychologists using the Movement Assessment Battery for Children, 2nd edition (MABC-2) [25]. MABC-2 is a test of coordination disorders for children aged 3–16 years. It consists of three fine motor measures, two ball skill measures, and three balance skill measures. Screening test scores, parent interviews and child examinations, and other test results were reviewed by multiple professionals, including child psychiatrists. If ASD is diagnosed or suspected, the child is added to the Autism Diagnostic Observation Schedule (ADOS)-2 [26], and they were assured of research reliability. The definitive diagnosis was determined on the basis of findings consistent with screening evaluation and diagnosis. We used the DSM-5 criteria for the diagnosis of ASD, ADHD, and both the DSM-5 and the European Academy of Childhood Disability guidelines [27] for the diagnosis of DCD. Criteria for ID were defined as an IQ <70.
