1. American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders, 4th edn., text revision Washington, DC; Author.
2. Ashwood, P., Kwong, C., Hansen, R., Hertz-Picciotto, I., Croen, L., Krakowiak, P., et al. (2008). Brief report: Plasma leptin levels are elevated in autism: Association with early onset phenotype? Journal of Autism and Developmental Disorders, 38, 169–175.
3. Autism and Developmental Disabilities Monitoring Network 2006 Principal Investigators. (2009). Prevalence of autism spectrum disorders—Autism and developmental disabilities monitoring network, United States, 2006. Morbidity and Mortality Weekly Report, 58(SS-10). http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5810a1.htm .
4. Autism and Developmental Disabilities Monitoring Network Year 2000 Principal Investigators. (2007). Prevalence of autism spectrum disorders—Autism and developmental disabilities monitoring network, six sites, United States, 2000. Morbidity and Mortality Weekly Report, 56(SS-1). http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5601a1.htm .
5. Baird, G., Charman, T., Pickles, A., Chandler, S., Loucas, T., Meldrum, D., et al. (2008a). Regression, developmental trajectory and associated problems in disorders in the autism spectrum: The SNAP study. Journal of Autism and Developmental Disorders, 38, 1827–1836.