FKBP5 and major depressive disorder: Since the seminal studies of [15] on the serotonin receptor gene 5-HTTLPR variant, a number of studies have reported interactions with child maltreatment with 5-HTTLPR and other genes such as FKBP5 and ADRB2, increasing vulnerability adult depression and PTSD [16–18] Gene x environment interactions have also been reported in children with less severe forms of environmental influences, such as the style of parenting behaviors.