TNF and obesity due to melanocortin 4 receptor deficiency: Unfortunately, anti-TNF treatment failure in patients with Crohn’s disease is common: One-quarter of patients experience primary nonresponse, one-third of responders lose response, and only 40% of patients are in remission at the end of a year.14,15 Anti-TNF monotherapy, obesity, smoking, disease severity, and the development of antidrug antibodies are associated with low drug concentrations and subsequent anti-TNF treatment failure.15,16 Carriage of the HLA-DQA1*05 allele confers a 2-fold risk of developing antibodies to anti-TNF treatment.17,18