Frequency and heritability of depression symptomatology in the second half of life: evidence from Danish twins over 45

Background. Self-reported depressive symptoms among the elderly have generated considerable interest because they are readily available measures of overall well-being in a population often thought to be at special risk for mental disorder.

Method. The heritability of depression symptoms was investigated in a sample of 2169 pairs of Danish twins (1033 MZ and 1136 same sex DZ) ranging in age from 45 to over 95. Twins completed an interview assessment that identified symptoms of depression, which were scored on Affective, Somatic and Total scales.

Results. Overall heritability estimates (a(2)) for the Affective (a(2) = 0.27, (95 % CI 0.22-0.32)). Somatic (a(2) = 0.26, (0.21-0.32)), and Total (a(2) = 0.29, (0.22-0.34)) scales were all moderate, statistically significant and similar to results from other studies. To assess possible variations in heritability across the wide age span, the sample was stratified into age groups in increments of 10 years. The magnitude of heritable influence did not vary significantly with age or sex. Somatic scale heritability tended to be greater for females than for males, though this difference was not statistically significant. The genetic correlation between the Affective and Somatic scales was 0.71, suggesting substantial common genetic origins.

Conclusions. Though the frequency of self-reported depressive symptoms increased with age in this sample, their heritability did not.