Analysis of a positional candidate gene for inflammatory bowel disease: NRAMP2

Genome scans have identified a region spanning 40 cM on the long arm of chr omosome 12 as a susceptibility locus for inflammatory bowel disease (IBD). This locus contains several candidate genes for IBD, one of which is the ge ne for the natural resistance associated macrophage protein 2 (NRAMP2). Thi s protein is a divalent cation transporter and is expressed in many cells a nd tissues. The putative role of this protein in innate immunity prompted u s to investigate a possible relationship between NRAMP2 and IBD. We assesse d the frequency of four restriction fragment length polymorphisms (IVS2+11A /G, IVS4+44C/A, 1254T/C, and IVS15Ex16-16C/G) in a group of 155 Crohn's dis ease (CD) patients, 114 ulcerative colitis (UC) patients, and 189 healthy c ontrols. Linkage analysis was performed in a group of 70 families with mult iple members suffering from IBD. We searched for additional intragenic mark ers and mutations by sequence analysis of the natural resistance-associated macrophage 2 gene of 33 CD patients, with a positive family history for IB D. We identified one novel restriction fragment length polymorphism in intr on 15 of the gene. The frequency of the rare allele is: 0.08 in our control population. An increased frequency of this allele was found in CD patients but this difference did not reach statistical significance. A weak associa tion between CD and homozygosity for the G allele of the IVS2+11A/G was fou nd (OR [odds ratio] = 2.2, CI [confidence interval] = 1.3-3.9, chi(2) = 8.4 , P = 0.013). Nonparametric linkage analysis and transmissions disequilibri um tests did not provide evidence for linkage of NRAMP2 to IBD, UC, or CD. Sequence analysis of the exons and the iron-responsive element in a panel o f 33 CD patients did not reveal any mutations in NRAMP2. Our association, l inkage, and sequence analysis in IBD shows that the putative genetic risk f actor on chromosome 12 likely is not NRAMP2. The weak association between t he G/G genotype of IVS2+11A/G and CD may be due to linkage disequilibrium w ith a nearby disease-causing gene.