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

Of the 559 children who underwent secondary assessment, 87 children (60 boys and 27 girls) were diagnosed with ASD. The 4-year mean ASD crude prevalence was 1.73% (95% CI 1.37–2.10%), with a 95% CI of 1.37 to 2.10%. Gender crude prevalence estimates for ASD were 2.35% (95% CI 1.76–2.94%) for boys and 1.09% (95% CI 0.68–1.51%) for girls, with the gender ratio of 2.2:1. After statistically adjusting for nonparticipants in comprehensive developmental assessment, the adjusted prevalence of ASD was estimated to be 3.22% (95% CI 2.66–3.76%). Gender-adjusted prevalence of ASD was 4.06% (95% CI 3.20–4.92%) in boys and 2.22% (95% CI 1.57–2.88%) in girls, with the gender ratio of 1.8:1.

The cumulative incidence of ASD by the age of 5 years within this research period (2013–2016) was 1.31% (95% CI 1.00–1.62%), with no significant increase in the 5-year cumulative incidence. The prevalence and 5-year cumulative incidence for each study year are summarized in **Table 1**.

Of the children with ASD (N = 87), 88.5% (n = 77) had at least one comorbid NDD (ADHD, DCD, ID, and/or borderline intellectual function (BIF)) and 20 children with ASD (23%) had 3 comorbid NDDs. Gender ratio of comorbidities was ADHD 50.6% (boys: girls = 2.4:1), DCD 63.2% (2.1:1), ID 36.8% (1.7:1), and BIF 20.6% (2.6,1) (**Figure 2** and **Table 2**).

Only 21 of 87 ASD children had received a diagnosis of ASD prior to this study. Of the 59 children who were assisted by the age of 5 years, 38 had other diagnoses (developmental or language delay). Twenty-eight (32%) had no developmental problems and no remedial intervention by the age of 5 years. **Figure 3** shows the problem of undiagnosed and unintervention of ASD.

Our study revealed that 5-year-old children with ASD have a high incidence of concurrent NDD, suggesting that ASD has a wide range of difficulties in daily life, such as attention and motor control, in addition to social problems. In infant screening, it is necessary to broadly evaluate various characteristics and provide early developmental support to children.

*Epidemiology of ASD in Preschool-age Children in Japan DOI: http://dx.doi.org/10.5772/intechopen.108674*


#### **Table 1.**

*Crude prevalence, adjusted prevalence, and cumulative incidence up to the age of 5 years of autism spectrum disorders in each survey year.*

**Figure 2.** *Number of comorbidities of autism spectrum disorder.*

For this reason, children who were diagnosed with some form of NDD at a health checkup were promptly given support and prepared for entering elementary school. Children who have been diagnosed with the disease should visit the Hirosaki University Hospital regularly at least once every 1 to 2 years for examinations and consultations and follow up until the age of 15 years to reconsider the diagnosis and determine the need for treatment. Some children require medication. The effects of these interventions need to be analyzed separately.


#### **Table 2.**

*Comorbid patterns of neurodevelopmental disorders in 87 individuals with ASD.*

## **2.4 Prevalence of sleep problems in Japanese Preschoolers and children with developmental disabilities**

Sleep problems are not only associated with emotions and behaviors but also affect mental and physical health over time. Our previous study reported 80% of 482 children had sleep problems in Japan [28]. Among Chinese urban kindergarten children, also, almost 80% (78.8%) of the children scored above the original Children's Sleep Habits Questionnaire (CSHQ ) cutoff point for global sleep disturbance [29]. However, there has been no report of a larger-scale study and the comorbid rate of neurodevelopmental disorders. The aim of this study was to estimate the prevalence of sleep problems in preschoolers and children with developmental disabilities using the Children's Sleep Habits Questionnaire (CSHQ ), which is widely used in large community-based surveys.

Subjects were 1800 children who participated in 5-year-olds developmental checkup in a city, Japan. Six hundred and nine participants in the secondary checkup were diagnosed whether NDD or not according to DSM-5 criteria. The data include 1421 TDs (boys: girls = 726:695), 118 ASDs (83:35) and 125 ADHDs (79:46), and 136 other DDs (91,45). Caregivers of 5-year-old children completed CSHQ. We compared with CSHQ total and subscale scores in four groups using Kruskal–Wallis's test and analyzed the relation between z-score of CSHQ total and subscale and diagnosis using a logistic multiple regression analysis (p < 0.05).

Children's Sleep Habits Questionnaire (CSHQ ) consists of nine subscales: Bedtime Resistance, Sleep Onset Delay, Sleep Duration, Sleep Anxiety, Night Waking, Parasomnias, Sleep Disordered Breathing, Daytime Sleepiness, and Sleep/ wake patterns [30].

Percentage of children suspected of having sleep problems (CSHQ co > 41) was 80% in TD, 89.0% in ASD, 90.4% in ADHD, and 83.8% in Other DD, respectively (see **Figure 4**). ASD and ADHD children have significantly higher scores of Total score, Sleep Duration, Sleep Anxiety, Parasomnias, Sleep-Disordered Breathing, and Daytime Sleepiness than TD (see **Figure 5**). When the CSHQ total score z-score increases by 1 (1SD), the probability of being diagnosed with ASD increases by 1.45 odds.

This study showed Japanese preschoolers have high percentage of sleep problems. In addition to comorbid rate of those in ASD were so high that we can predict ASD diagnosis from CSHQ. We must pay attention more that many children have sleep problems, and it would occur some health problems in the future.

**Figure 3.**

*The problem of undiagnosed and unintervention of ASD.*

**Figure 4.** *Comparison of the probability of sleep disorders by diagnosis in 1800 preschoolers.*
