Replication and extension studies of inflammatory bowel disease susceptibility regions confirm linkage to chromosome 6p (IBD3)

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the i ntestine, commonly diagnosed as either ulcerative colitis (UB) or Crohn's d isease (CD). Epidemiological studies have consistently shown that both gene tic and environmental factors influence the pathogenesis of IBD. A number o f genome scans have been conducted in cohorts of IBD families with affected sibling pairs (ASPs) to identify chromosomal regions that harbour IBD susc eptibility genes. Several putative linked loci have been identified, includ ing two loci on chromosomes 16 and 12, IBD1 and IBD2, which have subsequent ly been replicated by independent region-specific studies. We have conducte d both a replication study on another linkage region, chromosome 6p (IBD3), and extension studies on two other regions, chromosomes 3p and 7q. Microsa tellite markers across each region were genotyped in 284 IBD ASPs from 234 families. A nonparametric peak multipoint LOD score of 3.0 was observed nea r D6S291, replicating the previous linkage to chromosome 6p (IBD3). Nominal evidence of linkage was observed at both the 3p and 7q regions.