INCIDENCE OF ANTIPHOSPHOLIPID ANTIBODIES IN PATIENTS WITH MONOCLONAL GAMMOPATHY OF UNDETERMINED SIGNIFICANCE

The incidence of antiphospholipid antibodies in patients with monoclon al gammopathy of undetermined significance (MGUS) was studied. Antipho spholipid antibodies were measured in the sera of 93 patients (49 wome n, 44 men; mean age 70 [+/- 21] years) with MGUS by using an enzyme-li nked immunosorbent assay (ELISA). The phospholipids tested were cardio lipin (CL), phosphatidylserine (PS), phosphatidylinositol (PI), phosph atidylglycerol (PG), phosphatidic acid (PA), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). Positive results were defined as a value higher than the number of multiples of the mean per phospholipi d, which included 76 of 80 (95%; 20 age-matched) control individuals. The immunoglobulin-G (IgG) or IgM antiphospholipid antibodies isotype varied among the patients, as did the phospholipid specificity. For Ig G, PI was found elevated in 32% of the MGUS samples, whereas the other phospholipid antigens ranged from 9% to 15%. The percentage of patien ts with IgM antiphospholipid antibodies was higher. The authors observ ed PS, PI, PA, and PC as positive in 45%, 35%, 25%, and 25% of patient s, respectively. Of the 12 sera studied for IgA isotype, three (25%) w ere positive for PS, six (50%) for CL, and none for PE. Patients with MGUS manifested a significantly higher (P <.01) incidence of antiphosp holipid antibodies in their blood than did the control persons. No dif ference in the incidence of antiphospholipid antibodies was seen betwe en younger and older (age-matched) control patients. No correlation wa s found between serum levels of immunoglobulins and optical density re ading of the blank plates used as ELISA controls.