Genome Wide Profiling Of Chromosomal Abnormalities In 37 Patients With Monoclonal Gammopathy Of Undetermined Significance (MGUS)

The incidence of clonal DNA copy number alterations (CNAs) in plasma cells (PCs) is considered as one of the most important and independent prognostic factors in patients with multiple myeloma (MM). Also in the premalignancy MGUS, there are specific chromosomal changes in PCs such as del(13)(q14), IGHtranslocation, gain(1)(q21) and hyperdiploidy. However, not much is known about their significance in relation to malignant transformation. Also, MGUS research is further complicated by small number of malignant cells that could be obtained from patients.

Array-CGH technique optimization and DNA CNAs analysis in relation to prognosis at genome-wide level in MGUS patients.

We have analysed 37 MGUS patients (22M/15F; median age 62) using array-CGH, Agilent platforms “Human Genome CGH, 4×44K” (n=10) and “SurePrint G3 CGH+SNP, 4×180K” (n=27). DNA was isolated from separated PCs (using CD138, CD19 and CD56 markers) and amplified by multiple displacement amplification (MDA).

CNAs were observed in 57% (21/37) MGUS patients. Numerical and structural CNAs were found in 46% (17/37) and 41% (15/37) MGUS patients, respectively. We distinguished two genetic subgroups similar to MM patients: hyperdiploid and non-hyperdiploid. Hyperdiploidy was present in 32% (12/37) MGUS patients. The most frequent whole-chromosome gains were: 9 (83%, 10/12), 19 (83%, 10/12), 3 (75%, 9/12), 11 (67%, 8/12) and 15 (58%, 7/12). Non-hyperdiploidy was detected in 68% (25/37) MGUS patients. In both, hyperdiploid and non-hyperdiploid subgroups we have found loss of chromosomes 13 (25% vs. 20%) and Y (17% vs. 4%). Loss of chromosome 8 was detected only in hyperdiploid subgroup (8%) and losses of chromosomes 21, 22 and X only in non-hyperdiploid subgroup (8%, 4% and 8%, respectively). Structural changes were significantly more often present in hyperdiploid than in non-hyperdiploid patients (67% vs. 28%, p<0.05). We have identified whole-arm chromosome changes 1q gain and 16q loss in both hyperdiploid and non-hyperdiploid patients (17% vs. 12%, 8% vs. 8%, respectively), but 16p gain was seen only in hyperdiploid patients (8%). Segmental chromosome changes were also present in both hyperdiploid and non-hyperdiploid patients (58% vs. 24%). Interestingly, we have detected more segmental losses (15 vs. 8) and gains (6 vs. 2) in hyperdiploid than in non-hyperdiploid patients, but size median of these losses (3.33 Mb vs. 19.6 Mb) and gains (36.1 Mb vs. 63.5 Mb) was smaller in hyperdiploid than in non-hyperdiploid patients.

Moreover, we found one MGUS patient who has progressed to MM and required therapy after 6 months from MGUS diagnosis. Genome-wide profile of MGUS patient was especially unique by high number of structural changes (n=11) compared to other 15 MGUS patients with structural CNAs (median 1; 1 – 6). MGUS patient’s profile showed hyperdiploidy (gains of chromosomes 3, 5, 9, 11, 15 and 19), losses of chromosomes 8, 13 and Y, 7 segmental losses in areas 1p34.2-p13.1, 6p23, 6q12-q27, 7q36.3, 12p12.1-p11.23, 12q12, 12q21.2-q23.3 and 4 segmental gains in areas 6p25.3-p23, 6p23-p11.1, 6q11.1-q12, Xq21.33-q28. In addition, gains and losses, which included whole or large parts of chromosomes, showed unusual profile associated with other alterations. These findings have suggested a complex karyotype.

In our study we have optimized protocol of array-CGH analysis from amplified DNA and we have used it in first 37 MGUS patients. We found there are various chromosomal changes (numerical, whole-arm and segmental) in more than half of MGUS patients. Similar to MM, hyperdiploid and non-hyperdiploid genetic subgroups were identified. We also described one MGUS case with unique genome-wide profile indicating unfavourable prognosis.

NT13492, NT13190, NT11154, OPVK CZ.1.07/2.3.00/20.0183, MSM0021622434, GAP304/10/1395

No relevant conflicts of interest to declare.