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Objective Nucleotide‐binding oligomerization domain‐containing protein 2 (NOD2) gene mutations are known to be an important risk factor in the pathogenesis of Crohn's disease (CD). Specific disease phenotypes are associated with the presence of NOD2 gene mutation. One treatment option is to use an anti‐tumor necrosis factor (TNF)‐α agent. Therapeutic drug monitoring (TDM) is usually performed in cases of a loss of response. Our aim was to explore whether NOD2 gene mutations have an effect on the disease phenotype, vitamin D levels, and on TDM in CD patients. Methods This was a retrospective genotype–phenotype association study on NOD2 gene mutations in 161 patients with CD. Results Altogether 55 (34.2%) patients carried at least one mutant allele of NOD2. NOD2 gene mutations were associated with ileocecal disease, ileocecal resection, stricturing and perianal disease, and patients with NOD2 gene mutation had significantly less frequent colonic disease and received an ostomy less frequently. TDM in patients with NOD2 gene mutation showed more frequent anti‐TNF trough levels in the subtherapeutic range and lower anti‐TNF trough levels than in NOD2 wild‐type (WT) patients. Conclusions CD patients with NOD2 gene mutation have a specific clinical phenotype and they may require higher doses of anti‐TNF agents to achieve sufficient anti‐TNF trough levels. They may therefore benefit from a proactive TDM than a reactive approach. This could be another step in the direction of personalized medicine.

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