A shared cryoglobulin antigen in familial cryoglobulinemia.

Ten members of 3 generations of a family have IgM-IgG cryoglobulins and rheumatoid factors in their sera; one additional member has rheumatoid factor but not cryoglobulins. The disorder occurs in an autosomal dominant pattern. Here we describe an antigen, first identified on the cryoglobulin IgM of the index case, which is present in the sera of all 11 members of this kindred with rheumatoid factor. This antigen has the serologic properties of an IgM rheumatoid factor idiotype.