Patients with deficiencies in C1 components usually develop SLE: specifically, 91% of individuals with C1q deficiency and 60%‐66% of individuals with C1r‐C1s deficiencies.9, 11 The levels of C1s in SLE patients have not been studied in detail. The gene discussed is C1S; the disease is immunodeficiency due to a classical component pathway complement deficiency.