Genetic and non-genetic subtypes of major depressive disorder

Abstract

BackgroundWe aimed to examine the hypotheses that major depression is aetiologically heterogeneous consisting of a mixture of ‘genetic’ and ‘non-genetic’ forms or, alternatively, a mixture of one form that is ‘pure’ depression and another that has a familial relationship with alcohol dependency or other disorders.MethodOne hundred and eleven twin pairs (44 monozygotic, 67 dizygotic) where the proband had received treatment for DSM–IV major depression were ascertained via a hospital register. Family history information on parents and siblings was obtained from the proband, co-twin or both. Diagnoses on parents and siblings were made blind to twin zygosity or concordance and compared in the relatives of concordant versus discordant twins.ResultsThe lifetime prevalence and age-corrected risk of depression were no different in the relatives of concordant and discordant twin pairs. There was a marginally significant increase in the rate of alcohol abuse or dependence among the relatives of concordant twins but no difference between concordant and discordant pairs in respect of other axis I diagnosis among family members.ConclusionsThe results argue against genetic heterogeneity and suggest that major depression cannot usefully be divided into genetic and non-genetic forms or into ‘pure’ depression and depression associated with other disorders such as alcohol dependency.