SLC6A1 and bipolar disorder: The third greatest enrichment was for functions related to neurological regulation, including strong candidate genes for psychiatric disorders such as SLC6A1, GNAI3, PTGS2, and CTNND2. Given the association between increasing parental age and schizophrenia, bipolar disorder and autism in offspring, studies of shifts in the methylation of these genes in offspring of older parents are warranted.