This difference seems so insignificant. Goodwin et al. Women born of alcoholic parents and raised by their biologic alcoholic parents showed a significant increase in depression over controls, but women of alcoholic parents who were brought up by adopted parents did not show any increase in depression. Wender et al. All studies show a relationship between alcoholism and depression in relatives who have been separated by adoption.
Some adoption studies suggest a genetic factor in unipolar depression but more data is needed.