The aims of the national population-based study on Autism Spectrum Disorder (ASD) include: (1) to understand the overall prevalence of ASD in children aged 6-12 years in 8 cities (n=120,000), (2) to explore environmental and genetic risk factors associated with ASD

The study is a multicenter, cross-sectional study involing eight cities. The program includes a prevalence study and a risk factors analysis.

1. Prevalence study on ASD To estimate the national prevalence of ASD in Chinese pediatric population aged 6-12 years.

   1.1. Target population This 4-year study is initiated in the year of 2013 in eight cities of China . For each city, 3 communities with different economic levels were chosen including all children born within Jan 2001 to Dec 2007 (ages 6-12 years at screening) with local residency or have lived in the community over 6 months. The ASD children who are attending special education schools and meet with the inclusion criteria will also be included in the prevalence estimation.

   1.2. Sample size Based on the previous regional studies , we plan to recruit approx.15, 000 subjects for each city (average. 5,000 subjects for each community), and 120,000 subjects in total then comprise the national study sample. The plan will be updated, based on the prevalence obtained in the pilot study.

   1.3. Screening and diagnosis The screening tool will be chosen from Autism Spectrum Rating Scale (ASRS) or SRS（Social Responsiveness Scale） after pilot study.The questionnaire is a parent-administered form that takes approximately 15-20 minutes to complete. Parents of recruied children were invited to complete the questionnaire. Parents of all questionnaire screen-positive children will be contacted for appointing further diagnostic evaluations. Children whose parents could not be reached are classified as non-responders. The DSM-Ⅳ, ADI-R and ADOS (ADI-R: Autism Diagnosis Interview-Revised, ADOS: Autism Diagnosis Observation Scales) are used for diagnostic evaluations. Co-morbidities, such as epilepsy and ADHD (Attention Deficit Hyperactivity Disorder )after aditional medical examinations such as, EEG(electroencephalogram), head circumference, anthropometrics, allergies, sleep patterns, etc.

2. Risk Factors study on ASD A classic case-control design is applied to explore the risk factors of ASD. 2.1. Study subjects 2.1.1. Cases and control Cases were children living in target communities who are identified as positive based on questionnaire screen and the subsequent diagnosis with DSM-Ⅳ, ADOS and ADI-R.

Controls were children who are screened to be negative and matched to cases by age, gender, and class.

2.2. Environmental pollutants exposures Given the hypothesis that environmental factors might play a role in the etiology of ASD, we will analyze the biological samples of the subjects to investigate environmental exposures including chronic lead exposure, pesticides exposure, and endocrine disruptors exposure , for which, hair, blood, and urine will be collected for cases and controls. The detailed protocol for the measurement of each kind of biological sample has been introduced everywhere (see the references in individual block).

2.3. Analysis of other potential risk factors This study will also analyze the association between the onset of ASD and other risk factors, including diet (), living environment(),perinatal characteristics of parents, feeding history, baby growth and development after birth by using questionnaire and reviewing medical records.

2.4. Genetic analysis We are going to use the targeted area capture technology developed before and HiSeq2000, the second generation of high throughput sequencing platform, to carry out the molecular diagnosis screening (monogenic disease). Also, we will screen through Trio those ASD-related genetic mutations that are of high credibility and occur frequently so as to classify ASDs according to their definite etiologies.Furthermore, we will continue the study on the distribution of ASD relevant gene mutations among patients in China, which will lay a solid foundation for further studies of molecular epidemiology.Meanwhile, we will also apply genome-wide sequencing technology on the positive cases so as to find new mutation that might serve as potential molecular markers facilitating the diagnosis and treatment of ASDs.

A pilot study involving 4 cities (n=400 for each, in total n>=1600)will be conducted to test all methodology that will be applied in the prevalence study. A diagnostic study will be performed to evalute the performance of ASRS and SRS in screening ASD, one of which will be applied in the main study.

Inclusion Criteria:

• All children aged 6-12 years old and have lived in the recruied community over 6 months.

Exclusion Criteria:

• None

Community-based populations aged 6-12 years old form 8 cities in China