Correlation between Immunoglobulin Gene Rearrangements and Chromosomal Abnormalities in Multiple Myeloma.

Background: Multiple Myeloma (MM) is characterized by frequent and complex genetic abnormalities that contribute to the pathogenesis and its prognostic eterogeneity. There is evidence for two oncogenic pathways in the early development of clonal plasma cell disorder:

i) non-hyperdiploid carring translocation of the immunoglobulin heavy-chain locus and various oncogenes

ii) hyperdiploid tumors with infrequent IgH translocation.

The MM clonogenic cell is positively selected during the development and reaction of the germinal center. The immunoglobulin gene (IG) repertoire in MM follows a pattern similar to that of the normal repertoire. However, available data from analysis of IGH and IGK/L genes according to cytogenetic aberrations are limited. In the present study we investigated the frequency and characteristics of IGK and incomplete DJH as well as complete VDJH rearrangements in parallel with chromosomal abnormalities in a series of untreated MM patients. Materials and Methods. Bone marrow aspirates were collected from 53 MM patients with a mean age of 69.6 (range 48–84) between 2003–2007. The serum monoclonal component was IgG and IgA in the 77% and 22% patients respectively; 1 patient presented with IgD k MM. Cytogenetics and FISH analysis were performed simultaneously in 37 MM. In 18 (50.5%) samples kariotype analysis was successful. Interphase FISH analysis was perfomed using a set of probes specific for RB-1 (13q14), D13S319 (13q14.3), IgH (14q32), and p53 (17p13.1) loci, t(4;14), t(14;16), t(11;14) and a multicolor probe set for detection of aneuploidy (Vysis, Downers Grove, IL, USA). Genomic DNA was isolated for clonality analysis. IGHV-J, IGHD-J, IGKV-J, IGKV-KDE, IGKJ-C-INTRON-KDE rearrangements were amplified by PCR and analyzed following the BIOMED-2 protocol.

Results: Conventional cytogenetics allowed to detect 16 patients with a normal kariotype, 1 hyperdiploid kariotype with monosomy 13, 1 hyperdiploid kariotype with 3q21 deletion. FISH panel analysis resulted in 4 patients with hyperdiploid kariotype and 7 with abnormalities for RB-1 and/or D13S319. IGH rearrangements were detected in 3 patients and the t (4;14) was found in 1 case. The p53 deletion, t(11;14) and t(14;16) were not detected. The overall detection rate of clonality by amplifying VDJH and DJH rearrangements using family-specific primers was 90%. We found a high frequency (71.7%) of DJH rearrangements with DH3 segment under represented (4%). The DH7 segment was rearranged in the 15% of MM. Incomplete DJH and complete VDJH rearrangements were present at frequencies of 20% and 29.5%, respectively. IGK locus rearrangements were detected in 38 out of 53 MM and the 60% presented the non-productive IGKV-KDE and IGKJ-C-INTRON-KDE rearrangements. Parallel analysis of clonality pattern and chromosomal abnormalities showed that complete VDJH rearrangements were present in all hyperdiploid MM and in a small proportion (4/16) of the MM with normal karyotype.

Conclusions: Our results confirm previous estimations about IgH repertoire usage. Despite the small numbers, our findings indicate that complete Ig rearrangements might be correlated with hyperdiploid MM. Combining cytogenetics and IgH clonality studies might help to identify distinct subgroups of MM and provide a framework for dissection of disease prognosis and clinical management. Research funded by Regione Autonoma Sardegna.