A dominant feature of anxiety disorders is familial aggregation. However, the underlying mechanisms of between- and within-generational anxiety resemblance remain poorly understood. By disentangling the genetic v. environmental sources of familial resemblance in anxiety, we can help prevent within-family transmission of anxiety disorders. Therefore, data from both parents and twins are needed to obtain unbiased and detailed estimations of genetic and environmental sources of similarity between family members.

We examined data from 991 families with same-sex twins. Trait anxiety in twins was assessed via self-report and parent report, while parental trait anxiety was assessed via self-report. We established a nuclear twin family model and estimated genetic and environmental variances using two survey waves.

The results suggested that additive genetic (A), dominant genetic (D), and non-shared environmental (E) influences significantly contributed to trait anxiety, whereas familial environmental influences (F) and passive gene–environment correlations (rGE) did not. Sibling environmental influences (S) were only found in self-report data, and increased when genetic influences decreased from Wave 1 to Wave 2.

Our study highlights the important role of broad heritability in intrafamilial trait anxiety similarity. Parent–child resemblance occurred primarily due to shared genetic makeup rather than direct environmental transmission. Sibling-specific environments, as the only source of shared environments, need further investigation. These findings have both theoretical and practical significance for anxiety disorders. Future research can expand our understanding by examining the gene–environment interplay and sex differences.