Disseminated gonococcal infection secondary to a rare homozygous mutation resulting in complement factor I deficiency

A 34-year-old male presented with recurrent fever, arthralgia, and rash. He had two prior hospitalizations for suspected vasculitis and meningococcal meningitis at age 13 years. Positive blood cultures for <i>Neisseria gonorrhoeae</i> established the diagnosis of disseminated gonococcal infection. Complement studies showed low total (CH50) and alternative pathway (AP50) activity and low levels of all alternative and terminal complement proteins and the complement inhibitors factor H and factor I (FI), suggesting uninhibited complement activation and complement consumption. A homozygous nonsense mutation leading to a premature stop codon (p.Arg474*, or R456X) in <i>CFI</i> predicted complete FI deficiency, which was confirmed by immunoblotting. The patient's serum contained IgG against reduction-modifiable protein and the lipoproteins H.8 and lipidated azurin, which are targets for blocking antibodies against gonococci and meningococci, respectively. This report underscores the importance of considering FI deficiency in patients with invasive neisserial infections, vasculitis-like manifestations, and consumptive complementopathy.