title: Hereditary complement factor I deficiency.
abstract: 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.
authors.affiliation: Rheumatology Unit, RPMS, Hammersmith Hospital, London, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Vyse
authors.forename: P J
authors.initials: PJ
authors.lastname: Späth
authors.forename: K A
authors.initials: KA
authors.lastname: Davies
authors.forename: B J
authors.initials: BJ
authors.lastname: Morley
authors.forename: P
authors.initials: P
authors.lastname: Philippe
authors.forename: P
authors.initials: P
authors.lastname: Athanassiou
authors.forename: C M
authors.initials: CM
authors.lastname: Giles
authors.forename: M J
authors.initials: MJ
authors.lastname: Walport
mesh_terms: D000293:Adolescent; D002648:Child; D015932:Complement C3c / Q000172:deficiency; D017244:Complement Factor I / Q000172:deficiency* / Q000235:genetics; D003165:Complement System Proteins / Q000235:genetics; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D010375:Pedigree; D012008:Recurrence; D013290:Streptococcal Infections / Q000235:genetics
chemical_list: D015932:Complement C3c; D003165:Complement System Proteins; D017244:Complement Factor I