We recently described paratarg-7 (P-7), a protein of unknown function, as the target of 15% of immunoglobulin A (IgA) and IgG paraproteins in monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma. To determine the frequency of P-7 as a paraprotein target in IgM-MGUS and Waldenströ m macroglobulinemia (WM), sera from patients with IgM-MGUS/WM were tested for reactivity with recombinant P-7 by enzyme-linked immunoabsorbent assay.The specificity of the paraprotein-mediated reaction was shown by absorption studies and cloning of the respective B-cell receptor. The paraproteins of 18 (9 WM and 9 IgM-MGUS) of 161 patients (11%) reacted with P-7. Isoelectric focusing and phosphatase treatment showed that P-7 was hyperphosphorylated (pP-7) in all patients with an anti-P-7-specific IgM paraprotein tested. Because only 4 of 200 healthy controls (2%) were carriers of pP-7, pP-7 carrier state is associated with a significantly increased risk (odds ratio ‫؍‬ 6.2; P ‫؍‬ .001) for developing IgM-MGUS/MW. Family analyses showed that the pP-7 carrier state is inherited as a dominant trait. After IgA/IgG-MGUS and multiple myeloma, IgM-MGUS/WM is the second neoplasia associated with pP-7 carrier state. The dominant inheritance of pP-7 explains cases of familial IgM-MGUS/WM and enables the identification of family members at increased risk. (Blood. 2011; 117(10):2918-2923) IntroductionWaldenström macroglobulinemia (WM) is classified as an immunoglobulin M (IgM)-secreting B-cell non-Hodgkin lymphoma characterized primarily by lymphoplasmacytic infiltrates in the bone marrow accompanied by hypersecretion of monoclonal IgM. It corresponds to the lymphoplasmacytic lymphoma (LPL) as defined by the World Health Organization classification. 1 Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic precursor condition commonly preceding multiple myeloma (MM), and IgM-MGUS may precede development of WM. 2 Although age, race, sex, and preexisting IgM-MGUS are recognized risk factors, the cause of WM is largely unknown. Several studies have shown a significantly increased risk of WM after infections with hepatitis B virus, immunodefinciency virus, and rickettsiosis and found an increased risk of WM among persons with a personal history of autoimmune disease. 3 Genetic factors play an important role, with 20% of patients having a familial predisposition. Several studies of multiple affected families have been published, showing familial clustering of LPL and WM. [4][5][6] A recent study showed that family members of patients with MGUS and LPL-WM have a significant higher risk of MGUS/LPL-WM. 7 Environmental influences, chance occurrence, and inherited factors may all contribute to familial clusters. The evidence of somatic immunoglobulin gene mutations in WM indicates a role for antigenic stimulation in the development of WM. [8][9][10] A causal relationship between MGUS/WM and chronic antigenic stimulation has been suggested by the results of several studies. [8][9][10][11][12] Because of the rari...

3935 Poster Board III-871 Background Antigenic targets of paraproteins in MGUS, multiple Myeloma (MM) and WM might play a role in the pathogenesis of these neoplasms by chronic antigenic stimulation, but very few have been identified, of which most were specific for one individual paraprotein only. In contrast, we recently described paratarg-7, a protein of unknown function which is expressed in all human tissues as the target of 15% of IgA and IgG paraproteins in MGUS and MM (Grass et al.; Lancet Oncology 2009 in press). Methods To determine if and how frequently paratarg-7 functions as the antigenic target of the IgM paraproteins in MGUS/WM, sera from patients with IgM-MGUS/WM were tested for reactivity with recombinant paratarg-7 by ELISA. The specificity of the paraprotein-mediated reaction was demonstrated by absorption studies with recombinant paratarg-7 and by cloning the B-cell receptor from bone marrow cells of patients with a paratarg-7 specific paraprotein. Lysates of peripheral blood from patients and controls were tested by gel electrophoresis and isoelectric focusing before and after phosphatase treatment. Moreover, paratarg-7 cDNA was sequenced to exclude SNPs and mutations. Results The paraproteins of 18 (9 WM and 9 IgM-MGUS) of 161 (11%) sera from patients in Germany, USA and Greece reacted specifically with paratarg-7, proving paratarg-7 as the first antigen identified as a paraprotein target in a significant proportion of patients with IgM-MGUS/WM. Mutations or polymorphisms of paratarg-7 were not found. However, 2D-gelelectrophoresis, isoelectric focusing and phosphatase treatment revealed that paratarg-7 was hyperphosphorylated in all patients with an anti-paratarg-7 specific IgM-paraprotein tested. In contrast, only 4 of 200 (2%) healthy blood donors were carriers of hyperphosphorylated paratarg-7. Thus, carriers of hyperphosphorylated paratarg-7 have a significantly increased risk (odds ratio= 6.5; 95%-CI: 2.1-19.6; p=0.001) for developing IgM-MGUS/MW. Moreover, family analyses of relatives of IgM-MGUS/WM patients with an anti-paratarg-7 specific paraprotein revealed that the hyperphosphorylated state of this protein is inherited as a dominant trait. The results obtained in IgM-MGUS/WM are similar to recent observations made in 252 patients with IgG- or IgA-MGUS/MM where hyperphosphorylated paratarg-7 was also associated with a significantly increased risk of developing IgG- and IgA-MGUS (odds ratio: 7.9; 95% CI, 2.8-22.6; p=0.0001). Conclusions Hyperphosphorylated paratarg-7 is a highly significant risk factor for MGUS, WM and MM, with the highest odds ratio of any risk factor reported to date for these diseases. Hyperphosphorylated paratarg-7 is the first molecularly defined and dominantly inherited risk factor identified for any hematological neoplasm reported to date. The carrier state of hyperphosphorylated paratarg-7 explains cases with familial MGUS, MM and WM and enables the identification of family members of patients at increased risk for MGUS/WM/MM. That only MGUS/WM/MM patients who are carriers of hyperphosphorylated paratarg-7 had a paratarg-7 specific paraprotein suggests that the hyperphosphorylation of paratarg-7 induces auto-immunity and is involved in the pathogenesis of these diseases, e.g. by chronic antigenic stimulation. The identification of paratarg-7 as a frequent antigenic target enables the more detailed analysis of tumor-host interactions in these patients and its role in the pathogenesis of these diseases. Moreover, its dominant inheritance and the identification of familial cases with MGUS/MM/WM and hyperphosphorylated paratarg-7 carrier state facilitate genome-wide screens for the identification of the SNP responsible for hyperphosphorylation of this molecule. Disclosures: No relevant conflicts of interest to declare.