A population based family study of symptoms of anxiety and depression

Objective: To estimate an upper limit on the heritability of self-reported symptoms of anxiety and depression in a large and population representative nuclear family sample. Method: The ten-item symptom checklist (SCL-10) was administered as part of a health survey in a Norwegian county. The SCL-10 is a shortened version of the SCL-25, assessing symptoms of anxiety and depression. In all, 46,064 people responded, and with data from Statistics Norway, responses of first-degree relatives could be linked. Polychoric correlations between family members score on SCL-10 were calculated, and a structural equation model was fitted to these correlations using the software package R. Results: All correlations between nuclear family members were in the range of 0.12 to 0.16, indicating small but significant familial influences on SCL-10. In the best fitting model, heritability was estimated at 0.25 (95% CI = 0.22-0.27), and sibling specific environmental effects could be discarded. Conclusions: The estimated upper level heritability for SCL-10 in our sample was lower than what has been reported in twin studies of similar measures. (C) 2010 Elsevier B.V. All rights reserved.