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Ever since Freud described a 5-year-old with an impairing horse phobia arising from an environmental event (before cars were common), researchers have aimed to uncover pathogeneses of childhood anxieties. To examine genetic versus environmental transmission of anxiety symptoms, these investigators used a children-of-twins paradigm in which offspring (i.e., cousins) of monozygotic and dizygotic adult twins are compared. The cousins have a similar genetic background but are raised in different households.
Study data came from 387 monozygotic and 489 dizygotic twin families — same-sex cotwins (male, 37%; mean age, 45), their spouses, and one child of each pair (52% male, mean age, 16); cousins were matched by sex and differed in age by ≤4 years…