1). If the childhood maltreatment–AAD association arises because both are entirely due to genetic factors, rates of AAD in exposed individuals relative to unexposed individuals are expected to be equal among discordant MZ pairs (OR 1.0) but somewhat higher among discordant DZ pairs. This is because the MZ co-twins unexposed to maltreatment share all of the genetic risk factors that predispose to AAD in their maltreated co-twin, but the DZ co-twins share only half the genetic predisposition (model III, Fig. 1).
