Familial C1q deficiency associated with renal and cutaneous disease.

A familial C1q deficiency of complement in three siblings has been established. The patients were two brothers and a sister (12, 11 and 9 years old) with clinical and pathological features of Rothmund-Thomson syndrome (Poikiloderma congenital) and mesangial proliferative glomerulonephritis with diffuse IgM deposits. Abnormality has been defined as a total lack of CH50 haemolytic activity, undetectable C1q, failure to correct the defect with functionally pure C2 to C9 complement components, normal values for C2, C3, C4 and C5 and restoration of CH50 haemolytic activity when purified human C1q was added to the assay.