Unique and shared internalizing and externalizing genetic factors associated with suicidal thoughts and behaviors: Findings from the adolescent brain cognitive development study.

OBJECTIVE: Suicidal thoughts and behaviors (STBs) represent a tremendous public health problem among children and adolescents. Although internalizing (INT) and externalizing (EXT) phenotypes have been linked to STBs, less is known about the unique and shared genetic contributions of INT and EXT to STBs. METHOD: Participants were drawn from the Adolescent Brain Cognitive Development Study (ABCD) using multiple waves of data when children were 9-14 years old. We created polygenic scores (PGS) for INT, EXT, and their overlap (INT-EXT) based on a large-scale, multivariate genome-wide association study of INT and EXT phenotypes. RESULTS: We observed statistically significant positive direct effects of internalizing PGS to SA (β = 0.08, 95 % CI [0.04, 0.13]), externalizing PGS to passive SI (β = 0.06, 95 % CI [0.01, 0.11]) and active SI (β = 0.05, 95 % CI [0.002, 0.11]), and the INT-EXT PGS to passive SI (β = 0.05, 95 % CI [0.01, 0.10]), active SI (β = 0.10, 95 % CI [0.05, 0.15]), and SA (β = 0.10, 95 % CI [0.05, 0.14]). Additionally, all indirect effects of the internalizing, externalizing, and INT-EXT PGS on STBs through internalizing and externalizing phenotypes were statistically significant (β range = 0.015 to 0.053). CONCLUSION: Internalizing and externalizing genetic liabilities influence STBs through two pathways: one that is mediated by phenotypic internalizing and externalizing and another that is direct from genetic liability to STBs. Further research into targeted prevention strategies for child and adolescent STBs focused on both phenotypic and genetic measures of internalizing and externalizing is recommended.