A sarcoidosis genetic linkage consortium: The sarcoidosis genetic analysis (SAGA) study

Background: Sarcoidosis, a systemic granulomatous disease of unknown etiology, likely results from an environmental insult in a genetically susceptible host. In the United States of America, African Americans have a higher sarcoidosis incidence and suffer greater morbidity than Caucasians. Methods: A sarcoidosis genetic linkage study consortium was established to recruit African-American affected sib pair (ASP) families to identify chromosomal regions that may harbor sarcoidosis susceptibility genes and to determine if environmental factors modify any genetic effects. Results: We successfully met our goal of enrolling 359 ASPs using a multifaceted recruitment approach. In the total 559 sib pairs that were enrolled, genetic analyses revealed incorrectly specified relationships that required reclassification or removal from the analysis dataset of 10.4% of reported full and 1.4% of reported half sib pairs. The final study sample comprised 415 full and 104 half sib pairs with complete data. This included 338 ASPs. Within sib pairs, affection status was not associated with sex. Only 15 per cent of the 229 families had three or more affected sibs, but they contributed 42 per cent of the ASP total. Conclusions: The SAGA study experience should provide useful lessons and information to serve others in conducting genetic studies of complex diseases in African-American families.