Background: Major Depressive Disorder (MDD) is often comorbid with other heritable disorders. The correlates of a family history (FH) of mood disorders but not of comorbid disorders among MDD patients have been investigated. Since bipolar disorder (BD) is highly heritable, latent BD may bias findings.
Methods: The Vantaa Depression Study included 269 psychiatric out- and in-patients with DSM-IV MDD, diagnosed with semistructured interviews and followed-up for 5 years with a life-chart. The FH of mood, psychotic disorders, and alcoholism among first-degree relatives of 183 patients was investigated.
Results: Three fourths (74.9%) of patients reported a FH of some major mental disorder; 60.7% of mood disorder, 36.6% alcoholism, and 10.9% psychotic disorder. In multivariate regression models, a FH of mood disorder was associated with high neuroticism (OR 1.08 [1.02-1.15], p=0.014); a FH of alcoholism with alcohol dependence, number of cluster B personality disorder symptoms, and dysthymia (OR 2.27 [1.01-5.08], p=0.047; OR=1.11 [1.01-1.23], p=0.030; and OR 4.35 [1.51-12.5], p=0.007), and a FH of psychotic disorder with more time spent with depressive symptoms (OR 1.03 [1.00-1.05], p=0.043). However, after excluding those who later switched to BD, several of the associations abated or lost significance.
Limitations: Family history was ascertained only by an interview of the proband.
Conclusions: The majority of MDD patients have a positive FH besides mood also of other disorders. A mood disorder FH may correlate with higher neuroticism, alcoholism FH with alcoholism or personality disorders. FH studies of MDD should take into account the impact of patients switching to BD.
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