Hereditary complement factor I deficiency

TJ Vyse, PJ Spath, KA Davies, Bernard J Morley, P Philippe, P Athanassiou, CM Giles, MJ Walport

Research output: Contribution to journalArticlepeer-review


We describe four cases (from three families) of hereditary factor I deficiency, bringing the total number of cases now reported to 23. In one family there are two affected siblings: one has suffered recurrent pyogenic infections; the other is asymptomatic. In the second family, the patient had recurrent pyogenic infections and a self-limiting vasculitic illness; in the third family, the patient suffered recurrent pyogenic and neisserial infections. All four patients had markedly reduced concentrations of C3 in the serum (family 1 propositus: 28%; family 1 asymptomatic sibling: 15%; family 2: 31%; and family 3: 31% normal human serum) which was in the form of C3b. Low IgG2 levels may occur in primary C3 deficiency, and a reduction in IgG2 concentration to 1.14 g/l (normal: 1.30-5.90 g/l) was found in the patient from family 2. Using radioligand binding assays, we demonstrated increased binding of C3b to erythrocytes in a patient with factor I deficiency. This C3b could not be cleaved by autologous serum but could be cleaved by normal serum or purified factor I. We review and compare the published cases of C3, factor H and factor I deficiency.
Original languageEnglish
Pages (from-to)385-401
Number of pages17
JournalQJM: An International Journal of Medicine
Publication statusPublished - Jul 1994


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