Correct citation: Oliveira G, Ataíde A, Marques C, Miguel TS, Coutinho AM, Mota-Vieira L, Gonçalves E, Lopes NM, Rodrigues V, Carmona da Mota H, Vicente AM. Epidemiology of autism spectrum disorder in Portugal: prevalence, clinical characterization, and medical conditions. Dev Med Child Neurol. 2007 Oct;49(10):726-33.
I was puzzled as to why this was included, but the survey found "A diversity of associated medical conditions was documented in 20%, with an unexpectedly high rate of mitochondrial respiratory chain disorders." Poling and others have used this finding to claim that "up to 20% of children with autism have mitochondrial disorders".