For example, mitochondrial dysfunction is documented in many genetic syndromes associated with ASD, including Rett syndrome (12–14), PTEN mutations (15), Phelan-McDermid syndrome (16), 15q11-q13 duplication syndrome (17, 18), Angelman syndrome (19), septo-optic dysplasia (20), and Down syndrome (21, 22). This evidence concerns the gene PTEN and Rett syndrome.