C1q levels in hereditary angioedema.

In 21 affected members from 4 kindreds with hereditary angioedema, serum C1q levels generally were in the lower part of the normal range, with some values clearly below the lower limit of normal. The serum C1q levels in patients with hereditary angioedema were significantly depressed when compared with those in unaffected family members (p less than 0.001) and healthy control subjects (p less than 0.05). serum C1q levels were significantly (p less than 0.01) related to serum C4 levels which have been used as an indicator of disease activity in individual patients. C1q was stable during storage of serum samples at --20 degrees C for 60 days compared to storage at --70 degrees C. These studies indicate that depressed serum C1q concentrations may be seen in patients with hereditary angioedema and that the finding of this abnormality does not exclude the diagnosis.