Scl-70 antibodies are associated with more severe scleroderma disease. Anti-topoisomerase antibodies can be classified according to their immunoglobulin class (IgM, IgG or IgA). IgG-ATA is found most frequently in scleroderma, with IgA being quite common but IgM very infrequent. Ref Robbins 9/e pg 230