Deletions of chromosome 13q in monoclonal gammopathy of undetermined significance

Since deletion of chromosome 13q is a clinically relevant feature in multip le myeloma (MM), we analyzed bone marrow plasma cells from 29 patients with monoclonal gammopathy of undetermined significance (MGUS) to investigate t he chromosome 13 status in MGUS. Studies were performed by interphase fluor escence in situ hybridization (FISH) with a panel of 13q14-specific probes (RBI, D13S319, D13S25, D13S31). Plasma cells with a deletion of at least on e of the 13q14 loci were detected in 13 patients (44.8%) with MGUS. In five patients (17.2%), deletions of all four 13q14-specific probes were observe d, and the additional deletion of a 13q telomeric region (D13S327) suggeste d loss of the entire 13q arm or monosomy 13. Loss of 13q14 was observed to be monoallelic and to occur in 11.0 to 35.0% of plasma cells (cut-off level s for a deletion M10% with all probes). Nine of 77 patients (52.9%) with MM progressing from a pre-existing MGUS had evidence for a deletion of 13q14 as determined by FISH with the RB1 probe. These results suggest that deleti on of 13q14 is an early event in the development of monoclonal gammopathies , but its role for the eventual progression to MM remains to be determined prospectively.