Generalist Genes Contribute to Psychopathology Symptom Severity, but Specialist Environments Only Modestly Differentiate Problem Type during Adolescence: A Twin Analysis of Severity and Directionality of Internalizing and Externalizing Problems

The generalist genes specialist environments model of internalizing and externalizing problem comorbidity during adolescence was tested. As expected, symptom severity was primarily genetically influenced (generalist genes). However, directionality of problem type (internalizing vs. externalizing) was also considerably genetically influenced (specialist genes), with only modest evidence of specialist (non-shared) environments.