Objective: Celiac disease is a familial malabsorptive disorder with an estimated prevalence in first-degree relatives of 10-12%. The prevalence for first-degree and more distant relatives has not been determined in families where there are two affected first-degree relatives. The aim of our investigation was to estimate the prevalence and relative risk for celiac disease in relatives of two siblings diagnosed with celiac disease.
Methods: We ascertained sib pairs with celiac disease, and then identified all living first-degree relatives and available second-degree relatives to minimize ascertainment bias. We measured IgA endomysial antibodies, a highly specific and sensitive assay for celiac disease, in all subjects without a confirmed biopsy diagnosis. For those individuals with positive serologic tests, IgA tissue transglutaminase antibody tests and human leukocyte antigen DQA1 and DQB1 genotyping were performed for additional confirmation. Individuals with positive biopsy and/or serology were considered affected. We calculated the relative risk of being affected with celiac disease using the lambda(R) statistic.
Results: The prevalence of celiac disease in relatives of affected sib pairs was as follows: 21.3% (13/61) of siblings (lambda(S) = 53); 14.7% (10/68) of offspring (lambda(O) = 37); 17.2% (28/163) of first-degree relatives; 19.5% (16/82) of second-degree relatives; and 17.8% (52/292) of all relatives (lambda(R) = 44.5).
Conclusions: In these families, we identified a sibling risk approximately double that found in previous reports, as well as significant risk for more distant relatives, probably because of sharing of a common gene. In families where at least two siblings have been diagnosed with celiac disease, relatives are at high risk for celiac disease. Screening should be considered for all family members.