A Study of the Association Between Autism and Immune Changes in the Brain

Background: \- People with autism and autism spectrum disorders have problems with communication, behavior, and socializing, and many also have intellectual and developmental disabilities. The cause of autism is not known, but previous research has suggested an association between autism and immune changes in the brain. Researchers are interested in using the experimental radioactive drug (11C)PBR28, which attaches to a protein in the brain that is involved in immune changes, in positron emission tomography (PET) scanning of people with and without autism to see if there are greater immune changes in those with autism. Objectives: \- To determine if positron emission tomography scanning can be used to evaluate changes in an immune system protein in the brains of people with autism. Eligibility: \- Individuals between 18 and 45 years of age who have been diagnosed with either autism or autism spectrum disorders, or are healthy volunteers. Design: * Participants will be screened with a physical examination and psychological examination, medical history, questionnaires about behavior and mood, and blood and urine tests. * Participants will have two imaging studies of the brain at separate study visits. The first study visit will involve a magnetic resonance imaging (MRI) scan to provide a baseline image of the brain. The second study visit will involve PET scan with the radioactive chemical (11C)PBR28 to study immune system proteins in the brain. The MRI scan will take about 40 minutes, and the PET scan will take about 2 hours. * Participants will have a final study visit 24 hours after the PET scan to provide a final blood sample for testing.