C1q is a protein playing a role in the immune system. It is a component of the complement system, a complex network of proteins defending against various threats. C1q helps the body recognize and deal with foreign substances and damaged cells.
The Role of C1q in Immunity
C1q functions within the classical complement pathway. It initiates this pathway by binding to antibody-antigen complexes, formed when antibodies attach to foreign invaders like bacteria or viruses. This binding causes a change in the C1 complex, leading to a cascade of events that help clear pathogens. Beyond recognizing antibody-bound targets, C1q also directly binds to the surface of certain pathogens, activating the complement system without antibodies. C1q is also involved in clearing away dead or dying cells, known as apoptotic cells, and immune complexes. This clearance prevents inflammation and stops the immune system from mistakenly attacking its own tissues.
Understanding C1q Deficiency
C1q deficiency is a rare genetic disorder caused by mutations in the genes responsible for producing the C1q protein (C1QA, C1QB, or C1QC). It follows an autosomal recessive pattern, meaning an individual must inherit two copies of the mutated gene, one from each parent, to develop the deficiency. The deficiency results in either a complete absence of C1q protein or the production of a non-functional version.
Clinical manifestations often resemble systemic lupus erythematosus (SLE), an autoimmune disease. Over 90% develop SLE-like symptoms, which can include skin rashes that worsen with light exposure, joint pain, and kidney problems such as glomerulonephritis. They also have increased susceptibility to recurrent bacterial infections, including ear infections, urinary tract infections, and oral infections.
Diagnosis and Management
Diagnosing C1q deficiency involves a combination of clinical evaluation and specific laboratory tests. Healthcare providers will assess symptoms and medical history, looking for patterns consistent with the deficiency. Blood tests are then performed to measure C1q protein levels and evaluate overall complement activity.
An undetectable C1q level along with an absent total complement activity, but normal levels of other complement proteins like C2, C3, and C4, strongly suggests a congenital C1q deficiency. Genetic testing is performed to confirm the diagnosis by identifying mutations in the C1QA, C1QB, or C1QC genes.
Management of C1q deficiency focuses on addressing the symptoms and preventing complications. This may involve using immunosuppressive therapy, such as corticosteroids, to manage autoimmune symptoms like those seen in SLE. Antibiotics are prescribed to treat and prevent recurrent bacterial infections, and preventive measures like vaccinations may be recommended. In some cases, infusions of fresh frozen plasma (FFP) have been used to replace the missing C1q protein, helping to control symptoms.
Long-Term Outlook
C1q deficiency is a chronic condition that requires ongoing medical care. The long-term outlook for individuals with this deficiency varies depending on the severity of symptoms and the presence of complications. Without proper management, there is a potential for complications, including severe kidney disease and other organ damage due to persistent autoimmune activity and recurrent infections.
Early diagnosis and consistent management improve outcomes and quality of life for affected individuals. While some patients may experience relatively mild symptoms, others face severe manifestations, including life-threatening infections or neurological involvement. Regular medical follow-ups, adherence to treatment plans, and prompt attention to new symptoms mitigate the impact of C1q deficiency over time.