ADD1 and major depressive disorder: Regarding the differentially methylated positions found in first-episode, drug-naive adolescents with MDD, studies have found that the methylation of genes such as ACIN1, ACTR1A, ADCY7, ADCY9, ADD1, AMICA1, ANGPT2, ANK1, ANXA3, AP2A2, AP2B1, AP3B1, APP, ARIH2, ARTN, ATP1B1 and BAIAP2 in patients with depression is involved in the immune process, indicating an interaction between depression and inflammation-related diseases (23).