Genetic and environmental causes of variation in perceived loneliness in young people.

Loneliness is prevalent in adolescence, despite the widespread expectation directed to young people to start building close relationships beyond the nuclear family. The aim of the present study was to explore the causal genetic and environmental structure behind variability in adolescents' perceived loneliness. Seven national cohorts (ages 12-18 years) of Norwegian twins reared together (1,394 twin pairs) participated. Perceived loneliness was measured with five items from the UCLA Loneliness Scale. Data were collected from mothers, fathers, and twins' self ratings by means of a posted questionnaire. Biometric analyses were applied, testing the causal architecture of loneliness within a psychometric model with one common latent factor in addition to specific genetic and environmental sources influencing the scores of each informant. The results showed a heritability (h(2)) of 75% on the latent perceived loneliness factor, and nonshared environmental effects (e(2)) explaining the remaining 25% of the latent factor variance. There were also significant rater-specific genetic and nonshared environmental effects. No shared environmental effects were found in the model, and there were no sex differences in the estimates. This study showed that variation in perceived loneliness in adolescents is highly genetic. Additional genetic and nonshared environmental etiological sources are to some extent represented in the scores of the specific rater.