Familial association between allergic disorders and depression in adult Finnish twins.

Clinical studies have shown a relationship between allergic disorders and depression, panic disorder, attention deficit/hyperactivity disorder, and social anxiety for a significant subset of patients with these disorders. The nature of the relationship, whether due to shared environmental or biologic vulnerabilities or as a result of the stress of chronic illness, has been less clear. By examining the covariance of atopic disorders and depressive symptoms in a community sample of monozygotic (MZ) and dizygotic (DZ) twins, the contribution of genetic and/or shared environmental etiological factors can be established. A Finnish sample of 1337 MZ and 2506 DZ twin pairs, ages 33-60 years, was sent questionnaires inquiring about history of asthma, eczema, and atopic rhinitis, as well as the Beck Depression Inventory (BDI). The nature of the covariation between twins of these symptoms was investigated by fitting competing genetic and environmental models. Within-person correlation between atopic symptoms and BDI was 0.103 (P < 0.001) for the total sample. Using the Mx statistical modeling program to fit the data to competing quantitative genetic models, the best fitting model estimated that 64% of the association between atopy and BDI was due to shared familial vulnerability, primarily additive genetic influences. Although the measures for allergic disorders and depression are crude, this study supports the hypothesis that there is a small shared genetic risk for atopic and depressive symptoms, and if replicated, may open research for common mechanisms between allergic and depressive disorders. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:146-153, 2000. Copyright 2000 Wiley-Liss, Inc.