Von Willebrand factor cleaving protease (ADAMTS-13) in 123 patients with connective tissue diseases (systemic lupus erythematosus and systemic sclerosis).

BACKGROUND AND OBJECTIVES Autoantibodies inactivating the von Willebrand factor (VWF) cleaving protease, ADAMTS-13, are among the most frequent causes of thrombotic thrombocytopenic purpura (TTP). We evaluated whether or not ADAMTS-13 deficiency and autoantibodies inactivating the protease prevalent in patients with the prototypic autoimmune diseases systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). DESIGN AND METHODS We measured, in parallel, the protease and VWF antigen (VWF:Ag) in 123 patients, 36 of whom had SLE and 87 of whom had SSc. In 14 patients with either disease who had low plasma protease levels (below 40%) we also looked for anti-ADAMTS-13 inactivating antibodies. RESULTS ADAMTS-13 levels were significantly lower in SLE (p=0.0013) and in SSc (p=0.0002) than in normal controls. No anti-ADAMTS activity was measurable in patients with low ADAMTS-13 levels. VWF:Ag was high in both SLE and SSc (p=0.001). INTERPRETATION AND CONCLUSIONS Systemic connective tissue diseases are other conditions besides TTP that are associated in some instances with low but detectable levels of ADAMTS-13. Autoantibodies inactivating protease activity are not the cause of the low plasma levels of ADAMTS-13.