In some fibroblasts, especially those obtained from skin biopsies of SSc patients who were positive for anti-topo I, anti-RNA polymerase III and anti-fibrillarin autoantibodies, these alterations were associated with increased sumoylation of topo I. In contrast, the fibroblasts of anti-centromere positive patients showed unchanged sumoylation of topo I. Inhibition of SUMO1 gene improved catalytic function of topo I in SSc fibroblasts. The gene discussed is FBL; the disease is systemic sclerosis.