Four independent samples, i.e., the EA family sample, the EA case-control sample, the African American (AA) family sample and the AA case-control sample, were included in the present study. All subjects gave written informed consent as approved by the relevant Institutional Review Boards. The EA family sample (n=734) included 307 pedigrees (551 CD cases and 394 CIP cases). The AA family sample (n=834) included 316 pedigrees (664 CD cases, 432 CIP cases). The EA case-control sample (n=862) included 299 CD cases and 563 healthy controls. The AA case-control sample (n=619) included 406 CD cases and 213 healthy controls. Of the case-control samples, 175 EA CD cases, 403 EA controls, 136 AA CD cases and 48 AA controls were included in our initial study (Zuo et al 2007). Demographic characteristics are listed in Table 1.
