Delusional depression: further evidence for genetic contribution.

To quantify the contribution of genetic factors in the pathogenesis of delusional depression, the incidence of major depression in the first degree relatives of 77 delusional, 76 nondelusional depressive patients, and 153 age- and sex-matched controls was calculated in a case-control study. The morbid risk for psychiatric disorders, including major depression and bipolar I disorder, did not distinguish the two proband groups. The segregation analysis showed that the model of multifactorial inheritance fits best to our results. Heritability was estimated on the basis of a threshold model for multifactorial inheritance, and a high contribution of genetic factors for both subgroups was found.