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- CD, Crohn’s disease
- IBD, inflammatory bowel disease
- NPL, non-parametric linkage
- SNP, single nucleotide polymorphism
- UC, ulcerative colitis
Crohn’s disease (CD) and ulcerative colitis (UC) are the two main clinical subtypes of inflammatory bowel disease (IBD), a common complex disease with a frequency in Western populations of about 1 in 1000.1 A strong genetic susceptibility to IBD is supported by several epidemiological studies,2 and the existence of both specific and common susceptibility genes for CD and UC has been postulated.3
Several candidate loci for IBD have been identified following whole genome scans in different populations (reviewed in Bonen & Cho4). Among these, a locus in the pericentromeric region of chromosome 16 denoted IBD15 was found consistently in linkage to CD in several independent studies4 and in a large collaborative study by the IBD International Genetics Consortium.6 Most of these studies, with few exceptions,7 reported negative or non-significant linkage of the same locus to UC. Allelic variants of single nucleotide polymorphisms (SNPs) in the CARD15 gene, located in the IBD1 region, have since been demonstrated to confer susceptibility to CD, but not to UC in several populations8–10 (also reviewed in Bonen & Cho4).
In a previous study, we reported positive non-parametric linkage (NPL) scores in the IBD1 region in both our CD and UC families,11 with the highest scores occurring at markers D16S419 and D16S514, respectively. Marker D16S419 is located approximately 5 cM away from CARD15, while D16S514 is located almost 20 cM away on chromosome 16q. To follow up on these results, we typed 10 additional microsatellite markers in the chromosome 16 region of positive linkage in a total of 90 Italian IBD families, and repeated the linkage analysis after excluding 26 families with previously reported CARD15 SNP susceptibility alleles. The observation of a broad region of positive NPL scores in our UC families …