Peterson et al report their follow-up of a number of signals identified in recent genome-wide association (GWA) scans in Crohn’s disease. In addition to their relevance to paediatric Crohn’s disease, which to date appears similar to adult disease at a genetic level, their findings also illustrate a number of points relevant to the interpretation of case–control genetic association studies in general. It is worth detailing these, as a number of investigators find themselves with an irritable bowel disease (IBD) DNA resource and wondering about its utility as a replication set.

Although for a paediatric panel the data set used by Peterson et al is commendably sizeable, nonetheless in the context of the known effect sizes of the loci they were …