Immunodeficiency due to ficolin3 deficiency

Immunodeficiency due to ficolin-3 deficiency (also known as FCN3 deficiency or Hakata antigen deficiency) is an extremely rare primary immunodeficiency disorder caused by a deficiency of ficolin-3 (also called H-ficolin or Hakata antigen), a pattern recognition molecule of the lectin complement pathway. Ficolin-3 is encoded by the FCN3 gene and plays a critical role in innate immunity by recognizing acetylated compounds and certain carbohydrate structures on the surface of pathogens, thereby activating the complement system to facilitate pathogen clearance. The condition primarily affects the immune system, leaving patients vulnerable to recurrent and severe infections, particularly of the respiratory tract. Patients may present with recurrent pneumonia, lung abscesses, and necrotizing enterocolitis in the neonatal period. Cerebral abscesses and other invasive bacterial infections have also been reported. The deficiency impairs the lectin pathway of complement activation, reducing the body's ability to opsonize and destroy microorganisms effectively. Treatment is primarily supportive and includes aggressive management of infections with appropriate antimicrobial therapy. Prophylactic antibiotics may be considered in patients with recurrent infections. Fresh frozen plasma has been used as a source of ficolin-3 in acute settings. Long-term management focuses on infection prevention and monitoring for complications. Given the rarity of the condition, management strategies are largely based on case reports and expert opinion rather than clinical trials.

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