Evidence from twin studies indicates that major depression and alcohol dependence are genetically correlated. Kendler and colleagues (1993) found that, in a population of US adult women, the genetic correlation between the disorders was ~0.4–0.6. A study of adult male twins men (Lyons et al., 2006) found that, while a reciprocal causation model (whereby alcohol dependence increased the risk of major depression and vice versa) provided the best fit to the data, genetic correlation between these traits could not be ruled out.
