Peer Genetics Raise Depression Risk

Using Add Health data, the study exploits within‑school, across‑grade variation in same‑gender classmates’ average polygenic score for major depressive disorder. A one‑standard‑deviation rise in peers’ MDD score increases an individual’s depression probability by 1.9–3.8 points (larger for boys initially, persisting for women) and is linked to worse friendships, more substance use, and lower later socioeconomic status. This identifies social‑genetic spillovers in adolescent peer groups. — It reframes youth mental health and school policy by showing that peer composition’s genetic risk profile can causally shape outcomes, highlighting gene–environment interactions beyond individual biology.