Genetic populations were identified through Bayesian clustering using STRUCTURE (Gelernter et al 2005; Yang et al 2005). Because family-based association tests (FBAT) avoid confounding effects from model misspecification and population stratification or admixture (Laird et al 2000), we performed association tests in the EA family sample first, and then replicated positive results in the other three independent samples. To exclude the potential confounding effects on CD from other subtypes of comorbid SD, we adopted a one-by-one exclusion strategy described below.
