Complement Component 7 Deficiency

A number sign (#) is used with this entry because complement component 7 deficiency is caused by mutation in the C7 gene (217070).

Clinical Features

Boyer et al. (1975) described a woman with the Raynaud phenomenon, sclerodactyly, and telangiectasia (incomplete CRST syndrome; see 181750). X-rays showed no subcutaneous calcification, but the interosseous membrane between the radius and ulna was calcified. Severe deficiency of the seventh component of complement was found in the proband, and partial deficiency both in her parents and her 2 children. They considered the association of C7 deficiency and CRST syndrome to be coincidental, mainly because 2 other cases of CRST had high C7 levels.

Lachmann et al. (1978) described combined C6 (612446)-C7 deficiency. They suggested that C6 (217050) and C7 may function as a single genetic unit and that the primary transcript copied from the genome includes information for both proteins.

Zimran et al. (1987) determined the prevalence of complement 7 deficiency among 111 survivors of sporadic meningococcal disease. Ten had hereditary terminal complement deficiency: homozygous C7 deficiency in 4 and C8 deficiency in 6. No hereditary complement deficiency was found among 39 Ashkenazi subjects compared with 18% among 38 Sephardi subjects and 40% among 15 of Moroccan ancestry. The age at first presentation of meningococcal disease in complement-deficient patients was 14.7 years compared with 8.1 years in the nondeficient patients. None of the complement-deficient patients had meningitis below the age of 5 years versus 49% of nondeficient subjects; recurrent meningitis was observed in 40% versus 4%, and meningitis in sibs in 40% versus 2%, respectively. Among nonproband sibs, 11 cases of severe complement deficiency were found; 7 of the 11 had no history of meningitis or any other serious systemic disease.

Nurnberger et al. (1989) described an 11-year-old girl with recurrent meningococcal meningitis associated with complete absence of C7. The parents and 1 sister had normal levels of C7.

In a study of complement deficiencies among 101 patients who had a meningococcal disease, Schlesinger et al. (1990) found 11 unrelated persons with complete complement deficiency: 5 were deficient in C7, 3 in C8, 2 in properdin, and 1 in C2. All were in Sephardi Jews whose families originated from Morocco or Yemen in the case of C7 and C8 deficiency, or Tunisia in the case of properdin deficiency.

Friduss et al. (1992) described a severe, aggressive, and ultimately fatal pyoderma gangrenosum in a patient with congenital C7 deficiency.

Egan et al. (1994) described C7 deficiency in an Irish family in which 2 brothers had recurrent meningococcal infection.

Mapping

From studies of a family with C7 deficiency, Rittner et al. (1976) found no evidence of linkage to HLA. Neither C6 nor C7 is linked to HLA. Delage et al. (1977) excluded close linkage with HLA in a French-Canadian family. C2 deficiency was also present in the kindred.

C7 deficiency is caused by mutations in the C7 gene, which maps to chromosome 5p13 (Coto et al., 1991).

Molecular Genetics

Several mutations in the C7 gene in patients with C7 deficiency were reported by Nishizaka et al. (1996), Fernie et al. (1996), Fernie et al. (1997), and Fernie and Hobart (1998) (see 217070.0001-217070.0006).

Population Genetics

By screening for complement deficiencies in 145,640 blood donors from Osaka and combining their results with reports of 92,686 donors from throughout Japan, Fukumori and Horiuchi (1998) identified 5 individuals with C5 deficiency (609536), 6 individuals with C6 deficiency (612446), 17 individuals with C7 deficiency, 5 individuals with C8 alpha/gamma deficiency (613790), and 439 individuals with C9 deficiency (613825). A homozygous nonsense mutation (C728X; 217070.0001) and a homozygous frameshift mutation (217070.0002) in the C7 gene had been identified in 2 unrelated individuals with C7 deficiency by Nishizaka et al. (1996).