Familial resemblance for loneliness

Abstract

Social isolation and loneliness in humans have been associated with physical and psychological morbidity, as well as mortality. This study aimed to assess the etiology of individual differences in feelings of loneliness. The genetic architecture of loneliness was explored in an extended twin-family design including 8,683 twins, siblings and parents from 3,911 families. In addition, 917 spouses of twins participated. The presence of assortative mating, genetic non-additivity, vertical cultural transmission, genotype-environment (GE) correlation and interaction was modeled. GE interaction was considered for several demographic characteristics. Results showed non-random mating for loneliness. We confirmed that loneliness is moderately heritable, with a significant contribution of non-additive genetic variation. There were no effects of vertical cultural transmission. With respect to demographic characteristics, results indicated that marriage, having offspring, more years of education, and a higher number of siblings are associated with lower levels of loneliness. Interestingly, these effects tended to be stronger for men than women. There was little evidence of changes in genetic architecture as a function of these characteristics. We conclude that the genetic architecture of loneliness points to non-additive genetic influences, suggesting it may be a trait that was not neutral to selection in our evolutionary past. Sociodemographic factors that influence the prevalence of loneliness do not affect its genetic architecture.

Fig. 1

a Path diagram of social homogamy model. Squares represent the phenotypes of a DZ twin pair (P_T1 and P_T2) with one sibling (P_Sib), and both parents (P_F and P_M). Latent factors represent A-additive genetics, C-common environment, E-non-shared environment. Path coefficients represent r-variance due to non parental shared environment, f-cultural transmission, i-assortment. b Path diagram of phenotypic assortment model. Squares represent the phenotypes of a DZ twin pair (P_T1 and P_T2) with one sibling (P_Sib), and both parents (P_F and P_M). Latent factors represent A-additive genetic variance, D-dominance genetic variance, E-non-shared environment, and F-Vertical cultural transmission. Path coefficients represent s-gene–environment covariance, r-variance due to vertical cultural transmission, g-variance of additive genetic factors, i-assortment. c Path diagram of moderator model. β_a, β_d and β_e represent the moderating effects of the moderator (covariate) on the variance components A, D, and E, respectively. M₁ to M₂ represent the observed value on the moderator for twin 1 and twin 2. β represents the main effect of the moderator, with is included in the model for the means. μ is the intercept of the model for the means (Figure does not include the parents and sibling for simplicity)