IgG1 Subclass Restriction and Biochemical Peculiarities of Monoclonal Immunoglobulins in Scleromyxedema

International audience; Background: Scleromyxedema (SME) is a rare mucinosis associated with monoclonal gammopathy. Several biochemical peculiarities of monoclonal immunoglobulins (Ig) in SME patients were reported in case reports or short series, such as IgGλ over-representation, cationic migration, and partial deletion. Methods: Monoclonal immunoglobulins (Ig) from the serum of 12 consecutive patients diagnosed with scleromyxedema (SME) were analyzed using electrophoretic and immunoblotting techniques. Results: All monoclonal Ig from 12 SME were of IgG1 subclass, with an overrepresentation of the lambda-type light chain and a cationic mobility on standard zone electrophoresis, as compared with 21 cases of monoclonal gammopathy of undetermined significance (MGUS) of IgG1 subclass. Reactivity with specific monoclonal antibodies demonstrated no evident deletion of the heavy chain constant domains, which was also confirmed by analysis of Ig heavy chain molecular weight on a purified monoclonal component from one case. Conclusions: Significant isotype restriction of both heavy and light chains, and peculiar biochemical properties suggest that monoclonal Ig might be involved in pathophysiological events of SME.