Autism spectrum disorder (ASD) children have disturbances in language, perception, and socialization. Defects in oxidative phosphorylation (OXPHOS)/mitochondrial disease impacts cell energy functioning and may be the largest category of gene defects found in ASD, and may help to explain the heterogeneity of neurodevelopmental symptoms and identify a specific ASD subtype. OXPHOS defects can significantly impact brain development and functioning. In two large series, 17% to 20% of ASD patients had blood levels of chemicals suggestive of OXPHOS problems. Some ASD patients have also been reported with defects in their OXPHOS genes. OXPHOS diseases can start at any age and can even be triggered by exposure to certain chemicals, drugs, or stressors. This study will be the first comprehensive investigation of OXPHOS disease in ASD. Our short-term objective is to establish how OXPHOS defects relate to specific neurologic features in ASD, and develop testing that can easily identify ASD patients with OXPHOS, while a long-term goal is to use this information to develop treatment protocols of the dysfunction. We plan to compare 30 children with ASD plus OXPHOS, matched on age/sex/race and symptoms, with 30 children with ASD who have normal OXPHOS function, on neuropsychological tests, brain scans, and biochemical and genetic lab studies using easily accessible skin and blood cells to find the best indicators of OXPHOS genetic defects. This study will provide less invasive and more broadly available indicators of OXPHOS in ASD children, which then can be used in more in-depth studies.