Patients with versus without follow-up at this time point did not differ with regard to important baseline disease characteristics (BASDAI, ASDAS, elevated CRP, HLA-B27, classification as AS, age, peripheral arthritis, enthesitis, smoking, education, reason for discontinuation of first TNFi, physical exercise, body mass index) (see Additional file 1: Table S1). The gene discussed is CRP; the disease is enthesitis.