The interferon-gamma gene as a positional and functional candidate gene for inflammatory bowel disease.

Epidemiological and genome-wide linkage analyses have provided firm evidence for a genetic component in the pathogenesis of inflammatory bowel disease. The linkage regions on chromosomes 12 and 16 have been replicated in several independent samples. These represent the best positional evidence in the search for inflammatory bowel disease susceptibility genes. While systematic association and physical mapping studies in these regions are under way, the direct analysis of immunologically relevant genes as positional and functional candidates may provide a shortcut in this process. The interferon-gamma gene resides in the chromosome 12 linkage region near the marker D12S83. Interferon-gamma is an important proinflammatory cytokine in the interleukin-12 cascade and has been implicated in the pathogenesis of mucosal inflammation. We tested this gene for evidence of linkage and association in 133 German multiplex families and 506 single patients with their parents. An intragenic, highly informative CA-repeat marker in intron 1 of the gene was typed using fluorescence-labeled polymerase chain reaction and analysis on an automated sequencer. In the nonparametric linkage analysis using GENEHUNTER, a nonsignificant maximum LOD score of 0.67 was obtained. The transmission disequilibrium test for association was negative (P > or = 0.22) for Crohn's disease, ulcerative colitis, and the combined inflammatory bowel disease phenotype. In summary, the findings make interferon-gamma a very unlikely candidate for the major susceptibility gene in the chromosome 12 linkage interval. Future efforts can concentrate on other transcripts in the region.