For example, in Crohn’s disease, 10–30% of patients do not respond to the initial treatment (primary failure) with anti-TNF-α mAbs and up to 46% of patients lose response over time (secondary failure), potentially due to formation of anti-drug antibodies, ADA (22) As a result, routine therapeutic drug monitoring (TDM) for measuring trough drug levels and anti-drug antibodies is being actively considered in clinical practice (23, 24). The gene discussed is TNF; the disease is Crohn disease.