A systematic review of PubMed and Google Scholar was performed, limited to peer-reviewed articles and using the following search term combinations: (“early-life stress” OR “childhood adversity” OR “maternal deprivation” OR “postnatal stress”) AND (“epigenetics” OR “DNA methylation” OR “histone modification” OR “hydroxymethylation”) AND (“autism” OR “autism spectrum disorder” OR “ASD”) AND (FKBP5 OR NR3C1 OR MECP2 OR RELN OR GAD1 OR SHANK3 OR OXTR OR BDNF OR “HPA axis” OR “hypothalamic–pituitary–adrenal”). The gene discussed is GAD1; the disease is autism.