First-degree relatives are frequently affected in coeliac disease and dermatitis herpetiformis

Background: Coeliac disease and dermatitis herpetiformis are phenotypically distinct gluten-sensitive diseases. Coeliac disease is known to cluster in families, whereas there is little evidence for dermatitis herpetiformis and for the occurrence of both diseases in the same families. Methods: The Study group comprised 380 patients with coeliac disease and 281 patients with dermatitis herpetiforms. with a total of 3158 first-degree relatives, followed up for a mean of 14 years. The patients were questioned about affected first-degree relatives. The prevalence and incidence of biopsy-proven coeliac disease and dermatitis herpetiformis in relatives were determined. Results: Seventy-three (19.2%) patients with coeliac disease and 51 (18.1%) with dermatitis herpetiformis had affected first-degree relatives. The prevalence among relatives was similar for both diseases; 4.7% and 3.9% of the relatives had coeliac disease and 0.8% and 1.5% had dermatitis herpetiformis. respectively. The disease prevalence was 7% among siblings, 4.5% among parents and 3,5% among children. The annual incidence,vas 3/1000 relatives, which is 15 times higher than among the general population, Coeliac disease and dermatitis herpetiformis were mixed in several multiple-case families. Conclusions: The present long-term follow-up study of coeliac disease and dermatitis herpetiformis shows that every fifth patient can have affected first-degree relatives, and that the prevalence among relatives is 5.5%. Dermatitis herpetiformis segregates also in the families of patients with coeliac disease, and vice versa, indicating the same genetic background.