C1r/C1s Deficiency

**Semantic type:** Disease or Syndrome

**Definition:** Lack of production of either functional C1r or C1s protein, due to a genetic defect. Approximately 60% of patients with a C1r/C1s deficiency will develop a severe systemic lupus erythematosus at an early age. Patients also present with frequent sinopulmonary infections often with Streptococcus pneumoniae.