Patients with SLE have elevated B cell-activating factor (BAFF) levels promoting abnormal B cell activation and differentiation.5 Belimumab is a recombinant, immunoglobulin G1λ human monoclonal antibody that antagonises biological activity of soluble BAFF.6 Belimumab is the first treatment approved for children with cSLE.7–9. The gene discussed is TNFSF13B; the disease is systemic lupus erythematosus.