C1r/C1s Deficiency: A Patient Guide

Who this guide is for: This resource is intended for patients who have a confirmed, complete functional deficiency of C1r or C1s caused by biallelic (two) inherited genetic mutations. It does not apply to genetic carriers (who have only one mutated copy and usually no symptoms), those with isolated partial deficiencies, or those diagnosed with periodontal Ehlers-Danlos syndrome (pEDS).

C1r/C1s deficiency is an exceptionally rare genetic condition that affects the complement system, a vital part of your immune defense. In a healthy body, this system acts like a series of dominos; when it senses a threat, it triggers a cascade of proteins to destroy bacteria and clear away dead cells ^[1]. In people with a confirmed complete deficiency, the function of the “first dominos” of this classical pathway—the C1r and C1s proteins—is severely impaired or absent from birth. Because this condition is so rare, it is often discovered only after a patient has spent years navigating a “diagnostic odyssey” of unexplained infections or autoimmune symptoms ^[2][3].

Living with this deficiency involves managing a unique “dual threat” to your health. Because your immune system cannot effectively “see” and tag certain bacteria, you have an increased vulnerability to invasive infections from “encapsulated” germs, such as those that cause pneumonia and meningitis ^[4]. At the same time, because the classical pathway is also responsible for activating the cleanup of cellular “trash,” its absence causes debris clearance to be impaired. While this does not mean autoimmunity is inevitable, it significantly increases the risk that the immune system will eventually attack your own tissues, which can result in Systemic Lupus Erythematosus (SLE) or serious kidney inflammation known as lupus nephritis ^[5][2].

While there is currently no way to replace the missing proteins, the condition is manageable through a proactive, two-pronged approach. The first priority is building a defensive wall against bacteria through a rigorous schedule of specialized vaccinations and, in some cases, prophylactic antibiotics ^[6][7]. The second priority is long-term surveillance. By partnering with a team of specialists—including immunologists and rheumatologists—you can monitor your kidney function and immune markers closely. This individualized monitoring allows your care team to catch and treat inflammation early, helping you maintain your quality of life while navigating the complexities of this rare diagnosis ^[3][2].