Familial aggregation of Behçet's disease has been reported previously. The current study aimed at investigating the sibling recurrence risk ratio (lambda s) for Behçet's disease, which is of value in the estimation of the magnitude of genetic factors in the pathogenesis of Behçet's disease.
170 consecutive unrelated index cases (98 male, 72 female) were interviewed with a detailed questionnaire to ascertain their family trees and the manifestations of Behçet's disease in their relatives. Subsequently, the immediately older sibling, or if an older sibling was not available, the immediately younger sibling, was selected as the second sibling for the evaluation. These siblings were contacted by telephone, and all subjects with recurrent oral ulcers were invited for examination.
31 of the 170 index cases had 51 relatives fulfilling the International Study Group criteria. Among 166 second siblings, seven had Behçet's disease (six male, one female) and 22 siblings (eight male, 14 female) with recurrent oral ulcers were identified. Sibling recurrence rate-defined as the ratio of the risk of being affected among the siblings of patients and the risk of being affected in the general population- was found to be 4.2%, which gives a lambda s value for Behçet's disease of between 11.4 and 52.5 in Turkey.
A high lambda s value supports a strong genetic background for Behçet's disease which will be helpful in designing genetic linkage studies.