Comorbid Rate of Other Neurodevelopmental Disorder with Autism Spectrum Disorder in a Total Population Sample of 5-Years-Old Children.

Background: Recently patients with autism spectrum disorders (ASDs) have significant comorbidity of mental and physical disorders has well known. The distinct comorbid rate of other NDD with ASDs have been few extensively studied in preschool age based on behavioral criteria from the DSM-5.

Objectives: The objective of this study was to investigate the patterns of co-occurrence of neurodevelopmental comorbidities in ASDs in a Total Population Sample of 5-years-old children.

Methods: Using a total population sample in Hirosaki city in Japan (N=5016), all 5-year-old children in the catchment area underwent the screening phase annually from the year 2013 until the year 2016. Children who screened positive (using ASSQ, ADHD-RS, SDQ, DCDQ, PSI) were invited to comprehensive assessment, including child and parent interview (using DISCO, SRS-2, Conners-3, Sensory Profile), behavioral observation, cognitive testing (WISC-IV), and motor function testing (MABC-2, S-JMAP). The Autism Diagnostic Observation Schedule (ADOS-2) was conducted only for children whose parents agreed. All cases were discussed in a multidisciplinary research team, where ASD cases were ascertained based on the best clinical judgement. The same screening tools and diagnostic assessment batteries as well as diagnostic criteria (the DSM-5) were consistently used throughout the 4 study years. We estimated comorbid rate of other NDD with ASDs.

Results: Our study findings showed that only 11.5% (10/87) of 5-year-old children had ASDs alone; the remaining and that the rest of 88.5% (n=77) of children were found to have at least one co-occurring NDD (i.e. one or more among ADHD, DCD, ID, and/or borderline intellectual functioning). Of note, 20 cases (23%) had 3 co-occurring NDDs. Of eighty-seven 87 children who were diagnosed with ASDs, 44 children (50.6 %) were confirmed to have ADHD (male: female = 3:1), while 55 children (63.2 %) were identified to as having co-occurring DCD (male: female = 2.1:1). Co-occurring cognitive impairment was as follows; ID defined as (IQ below <70) in 32 children (36.8%) and Borderline Intellectual Functioning (70<IQ<85), defined as IQ between 70 and 85 in 18 children (20.7 %).

Conclusions: Our study suggested high rates of co-occurring NDDs of ASDs. The comorbid rates of ADHD and DCD in the present study might be higher than the findings from extant research.