Background. Clinical and epidemiological studies have reported an association between lifetime cigarette-smoking and panic attacks. Several explanations for this relationship have been proposed, mostly focusing on direct causal pathways. The objective of this study was to investigate a hypothesis of shared vulnerability by examining whether panic attacks and cigarette-smoking share genetic or environmental liability factors.
Method. Questionnaire data on 3172 female–female twins (1409 complete pairs), aged 18–31 years, from a population-based Norwegian twin registry, were used to calculate the correlation between genetic factors and the correlation between environmental factors that influence lifetime measures of panic attacks and daily smoking.
Results. The best-fitting biometrical twin model suggested that genetic factors influencing panic and smoking were uncorrelated. Shared or familial environmental factors were perfectly correlated, and accounted for 75% of the association between the phenotypes. The correlation between individual environmental factors influencing the phenotypes was 0·25 (0·07–0·44). In the full model, the genetic correlation was 0·17 (0·00–1·00), and genetic and shared environmental factors respectively accounted for 18% and 61% of the co-variance between panic and smoking.
Conclusion. The results suggest that panic attacks and lifetime smoking have few or no genetic liability factors in common. The shared environmental factors that influence the two phenotypes are identical. Liability to panic attacks in females appears to be more influenced by shared environmental factors than previously indicated by univariate studies.