Gene-environment interplay in depressive symptoms: moderation by age, sex, and physical illness

Abstract

Background: Numerous factors influence late-life depressive symptoms in adults, many not thoroughly characterized. We addressed whether genetic and environmental influences on depressive symptoms differed by age, sex, and physical illness.

Method: The analysis sample included 24 436 twins aged 40-90 years drawn from the Interplay of Genes and Environment across Multiple Studies (IGEMS) Consortium. Biometric analyses tested age, sex, and physical illness moderation of genetic and environmental variance in depressive symptoms.

Results: Women reported greater depressive symptoms than men. After age 60, there was an accelerating increase in depressive symptom scores with age, but this did not appreciably affect genetic and environmental variances. Overlap in genetic influences between physical illness and depressive symptoms was greater in men than in women. Additionally, in men extent of overlap was greater with worse physical illness (the genetic correlation ranged from near 0.00 for the least physical illness to nearly 0.60 with physical illness 2 s.d. above the mean). For men and women, the same environmental factors that influenced depressive symptoms also influenced physical illness.

Conclusions: Findings suggested that genetic factors play a larger part in the association between depressive symptoms and physical illness for men than for women. For both sexes, across all ages, physical illness may similarly trigger social and health limitations that contribute to depressive symptoms.

Keywords: Aged; depressive symptoms; heritability; twin studies.

Figure 1

Diagram of the additive genetic components from the age and I-CIRS moderated bivariate biometric model examining physical health (CIRS) and depressive symptoms (DEP). Note that slope a40 pertains to individuals age 40–75 while slope a75 pertains to individuals 75 and older. The equation for calculating the genetic covariance between I-CIRS and depressive symptoms is the product of the pathway shared between CIRS and depressive symptoms and the genetic pathway on CIRS. The equation can be written as: (a_Common + β_a40c * AgeA + β_as75c * AgeB + β_aCIRSc * CIRS) * (a_CIRS + β_a40CIRS * AgeA + β_a40CIRS * AgeB)

Figure 2

Graphs of the estimated unstandardized genetic and environmental variance components for depressive symptoms for men (panel A) and women (panel B) by age from combining the common and unique raw variance estimates from the AE age and I-CIRS moderated bivariate biometric model. Graphs of the estimated genetic, and non-shared environmental correlations between I-CIRS and depressive symptoms by I-CIRS score for men (panel C) and women (panel D) shown at age 75 for purposes of illustration. Notes: A = additive genetic variance; E = non-shared environmental variance; rG = genetic correlation between depressive symptoms and I-CIRS; rE = non-shared environmental correlation between depressive symptoms and I-CIRS. Shaded area represents 95% confidence interval of the estimate. The I-CIRS score was standardized so the mean CIRS score equals zero and with standard deviation equal plus or minus 10.