Heritability of individual depressive symptoms

Background: In attempting to understand the familial basis of depression, most studies have focused on broad indices of depression and mood change. Broad indices may not adequately reflect the heritable basis of depression because of an unexplored possibility that not all symptoms are heritable. Methods: The heritability of individual depressive symptoms was estimated from a sample of 343 general population volunteer twin pairs who completed the Beck Depression Inventory, the Centre for Epidemiologic Studies Depression Scale and items from the Symptom Checklist assessing depressive symptoms. Principal component analysis of the items extracted 14 factors that represented a wide range of depressive symptomatology. Results: The factors were differentially heritable (h2 range: 0.0–35.0%). The factors that have a heritable basis described endogenous or physiological functions (e.g. loss of appetite, libido/pleasure). Symptoms such as negative affect or tearfulness did not have a heritable basis, suggesting that these symptoms are responses to negative life events/experiences or a learned association to changes in physiologic function. Limitations: Relatively small size of the sample. Conclusions: Depressive symptoms are differentially heritable and the results suggest that future research, such as genotyping studies, separates heritable and non-heritable symptom clusters prior to analysis. This will help identify which genes are involved and what their function in depression may be, leading to the development of more targeted and effective therapies.