Association of immunoglobulin Km and Gm allotypes with specific antinuclear antibodies and disease susceptibility among connective tissue disease patients. The distribution of the immunoglobulin Km(1) and Gm phenotypes was examined in patients with connective tissue diseases, including systemic lupus erythematosus, mixed connective tissue disease, and scleroderma, whose sera were characterized for antibodies against nuclear antigens and polypeptides of U small nuclear ribonucleoproteins. We found a strong association between Km(1) phenotype and susceptibility to systemic lupus erythematosus (P less than 0.00001, relative risk = 17). We also found a positive association between the Km(1) phenotype and the presence of anti-double-stranded DNA antibodies. The presence of certain immunoglobulin genes or gene families may have a role in susceptibility to the development of autoantibodies and/or of connective tissue disease. 