Independent (i.e., unrelated) individuals were included who had ulcerative colitis with either left-sided or extensive disease (i.e., those with proctitis only were excluded); for further details on the precise definitions used, see the accompanying phenotyping manual (phenotyping-manual.pdf). Since the publication of Silverberg et al., we have learned that one individual had indeterminate colitis instead of ulcerative colitis (this individual was included in the published allelic association tests).

Individuals were also selected to be white, non-Hispanic of European ancestry. However, since the publication of Silverberg et al., we have learned that one individual was Trinidadian (this individual was not placed in an ancestry stratum and was therefore excluded from the allelic association tests).