Clinical and immunological studies in a case of selective complete C1q deficiency.

A 10-year-old male with recurrent skin lesions and chronic infections was found to have a selective deficiency of C1q after functional analysis of all complement components. The addition of highly purified human C1q to the patient's serum restored C1 activity, indicating the presence of C1r and C1s and the absence of C1q. Titration of highly purified C1q with patient serum as a source of C1r and C1s resulted in a linear dose-response curve. The undetectable CH50 activity temporarily returned to normal within a few hours of plasma infusion, but the C1 titres were still only 1–3% of normal. Following plasma administration, the peak of C1q activity was reached after 30 min and returned to undetectable levels within 24 hr. The patient serum was not anti-complementary when incubated with normal serum. Nine members of the family, including the parents and two healthy siblings, were subjected to complement studies and HLA typing. The C1 titres and CH50 activity were found to be normal in all except the paternal grandmother who showed reduced levels of all the complement components. There was no linkage for the gene of C1q deficiency and HLA antigens. Among the various laboratory studies performed, anti-smooth muscle antibodies, immune complexes and anti-HBsAg antibody were found to be positive. The child died of a disease compatible with septicaemia. Post mortem tissue studies by light, fluorescent and electron microscopy have shown the presence of a mesangioproliferative glomerulonephritis.