Familial clustering of hypochondriasis

INTRODUCTION: Hypochondriasis is a prevalent psychiatric condition associated with substantial individual suffering and healthcare utilization. Despite its clinical importance, little is known about its etiology, and the extent to which familial and genetic factors contribute to its development remains unclear. METHODS: In this population-based cohort study, we identified 5,809,325 individuals born in Sweden between 1950 and 2008 with information on both biological parents, excluding those who emigrated or died before age 6 or before 1997. From this cohort, we identified clusters of full siblings, half siblings, and cousins. We compared the risk of hypochondriasis among relatives of individuals diagnosed with hypochondriasis to that of relatives of individuals without hypochondriasis. Previously validated ICD-10 diagnoses of hypochondriasis were identified through the Swedish National Patient Register (NPR). Cox regression models with time-varying exposures and attained age as the underlying time scale were used to estimate hazard ratios (HRs). RESULTS: A total of 3,202 individuals were diagnosed with hypochondriasis (57% women; median age at first diagnosis 32.1 years). Relatives of individuals with hypochondriasis had a higher risk of the disorder, compared with relatives of individuals without hypochondriasis, and the risk increased with the degree of genetic relatedness. The strongest association was observed in full siblings (HR, 9.5; 95% CI, 5.1 - 17.5), followed by half siblings (HR, 5.6; 95% CI, 2.1 - 14.9), and cousins (HR, 2.6; 95% CI, 1.4 - 4.9). CONCLUSION: Hypochondriasis is a familial and likely heritable disorder.