OR2L13 and neurodevelopmental disorder: A previous systematic review aimed to summarize the evidence of epigenetic involvement in neurodevelopmental disorders without using limitations in source tissue for DNA extraction or patients’ ages [54]; it indicated that the OR2L13 gene, which encodes for an olfactory receptor, is a potential peripheral epigenetic marker for ASD, given that its methylation levels were found to be altered in two independent case–control investigations, one performed on buccal cells [55] and the other on peripheral blood [56].