C1q deficiency associated with urticarial-like lesions and cutaneous vasculitis.

We describe a 46 year old women with a seven year history of urticarial-like symptoms and cutaneous vasculitis with marked deficiency of C1q in the presence of normal levels of C1r and C1s and high titers of low molecular weight (7S) C1q precipitins. Hemolytic C1 activity, which was greatly reduced, was restored upon the addition of purified C1q. The other complement components were present in moderately reduced or normal levels. This patient bears resemblance to several other persons previously described with urticarial-like lesions in association with selective deficiency of C1q. The similarity of the clinical features, pathologic diagnosis, C1q levels disproportionately deficient in relation to other complement components and low molecular weight C1q precipitins support the conclusion that these are causally related in a symptom complex. The underlying basis is yet to be defined.