Chalkia D, et al. - In this present study, the experts evaluate what effect mitochondrial lineages encompassing ancient mitochondrial DNA (mtDNA) functional polymorphisms, termed haplogroups, have with autism spectrum disorders (ASD) risk. They reveal that mtDNA lineages must make a significant contribution to overall ASD risk as haplogroups I, J, K, O-X, T, and U encompass 55% of the European population.