Autism spectrum disorder (ASD) is an increasingly frequent neurodevelopmental disorder. A number of indications recently pointed to abnormal distributions of microRNAs (miRNAs) in autistic patients. The noncoding regulatory miRNAs are abundant in the developing brain and abnormal levels of expression of several of them were found in tissues of ASD patients. Here, we discuss the previously published results and compare them with our recent data identifying 6 miRNAs whose blood levels are downregulated in ASD patients. A similar although less pronounced decrease is hereditarily transmitted by the clinically unaffected parents of sick children and the sibling. Robustness of the finding was confirmed by similarly low levels of the six microRNAs in two established mouse models of the disease. Several hopeful avenues of research may be considered from these results including molecular mechanisms from the regulation of the miRNAs to the identification of their target genes and the non-Mendelian mode of inheritance of the autism-prone state. On the clinical side, they offer the possibility of a very early detection of the affected children.Keywords: Autism, downregulation, heredity, microRNAs, mouse model, parent.