Familial cryoglobulinemia and C4 deficiency.

The coexistence of cryoglobulinemia and C4 deficiency was found in one family. Twelve subjects were examined, most of them being asymptomatic. Cryoglobulins were found in 9 members and its type was defined in 6 of them, 3 having mixed IgM-IgG and 3 having monoclonal IgM cryoglobulins. The concentration of the third component of the complement system was normal in 10 subjects, while the concentration of the fourth one was found to be below the lower limit of normal in 9 subjects. Only C4 deficiency--and not cryoglobulinemia--was HLA-linked. There was no evidence of HBs antigenemia. The results of this study are discussed in the light of the pertinent literature.