Familial risks of anxiety have been assessed in small case-control studies, usually based on reported, but not medically verified anxiety in family members; thus the degree of familial clustering for this disease remains to be established.

This 1 January 1973 to 31 December 2004 study of the entire population of Sweden linked information on family relationships from the nationwide Multi-Generation Register with information from the nationwide Swedish Hospital Discharge Register on first diagnoses of anxiety. Standardized incidence ratios (SIRs) were calculated by comparing risk in siblings of persons hospitalized for anxiety with risk in persons whose siblings had no hospital diagnosis of anxiety.

The sibling risk was 3.02, which was independent of gender and age differences between siblings. The SIR was highest in siblings < 20 years of age (3.99). Analysis of subtype risk showed that having a sibling diagnosed with any anxiety disorder resulted in increased risk of a number of disorders; highest increased risk was of social phobias (SIR 4.70, 95% CI, 1.96-11.0). Risk of Panic disorder, generalized anxiety disorder, and mixed anxiety and depressive disorders was raised in female but not male siblings.

Heritable effects likely play an important role in the etiology of anxiety disorders, but the extent of their role remains to be established. Important contributions could be made by studies of gene-environment interactions that have sufficient sample sizes to produce reliable results.