Previous studies have indicated that, in general, human leucocyte antigen (HLA)-B27 positivity, younger age, shorter disease duration, male sex, and elevated C-reactive protein (CRP) levels are associated with higher response rates to tumour necrosis factor alpha inhibitors (TNFi) in patients with axial SpA, whereas obesity and smoking are associated with lower response rates [5–8]. The gene discussed is CRP; the disease is obesity due to melanocortin 4 receptor deficiency.