Phenotypic familial aggregation in chronic chilblains

BACKGROUND: Our clinical observations and two earlier studies indicate familial clustering to be involved in chronic chilblains. Demonstrating phenotypic familial aggregation is a next step to investigate the origin of familial clustering. OBJECTIVE: This study was initiated to assess evidence for phenotypic familial aggregation in chronic chilblains. METHODS: Using a case-control family design in a primary care setting, we computed the familial relative risk of at least one episode of chronic chilblains during life with 95% confidence intervals (CIs). The study population consisted of 192 relatives of 31 case probands (at least one confirmed episode of chronic chilblains). The control population consisted of 178 relatives of 31 sex- and age-matched index controls (no history of chronic chilblains). RESULTS: The familial relative risk of chronic chilblains was 3.6 (95% CI 1.9-7.3). Additional sensitivity analysis shows similar figures. CONCLUSION: We demonstrate robust phenotypic familial aggregation in chronic chilblains