['Ample evidence exists that Anti-tumor necrosis factor (TNF) concentrations during induction determine short and long-term outcome in inflammatory bowel disease (IBD). We investigated if a variable number of tandem repeats (VNTR) polymorphism in the neonatal Fc-receptor (FcRn), responsible for extending half-life of IgG, influences anti-TNF concentrations in patients with IBD.', 'Retrospective single-center study, including a cohort of 395 infliximab (IFX) naive IBD patients treated with IFX 5\u2009mg/kg on weeks 0, 2, and 6 and a second cohort of 139 adalimumab naive patients, treated with adalimumab 160-80-40\u2009mg on weeks 0, 2, and 4. Area under the serum anti-TNF concentration-time curve (AUC), from week 2 and 6 for IFX and week 2 and 4 for adalimumab, was used to identify factors influencing these drug concentrations.', 'The VNTR2/VNTR3 genotype was associated with a 14% lower IFX AUC compared with patients homozygous for VNTR3/VNTR3 (P=0.03), although this effect became apparent only when immunogenicity (26% lower concentrations, P=9 × 10'] Does a Genetic Variation in the Neonatal Fc-Receptor affect Anti-TNF Drug Concentrations in Inflammatory Bowel Disease?