DNA methylation analysis of tumor suppressor genes in monoclonal gammopathy of undetermined significance

Aberrant DNA methylation is considered an important epigenetic mechanism for gene inactivation. Monoclonal gammopathy of undetermined significance (MGUS) is believed to be a precursor of multiple myeloma (MM). We have analyzed methylation status of p15 (INK4B) , p16 (INK4A) , ARF, SOCS-1, p27 (KIP1) , RASSF1A, and TP73 genes in bone marrow DNA samples from 21 MGUS and 44 MM patients, in order to determine the role of aberrant promoter methylation as one of the steps involved in the progression of MGUS to MM. Methylation specific polymerase chain reaction assay followed by DNA sequencing of the resulting product was performed. SOCS-1 gene methylation was significantly more frequent in MM (52%) than in MGUS (14%; p = 0,006). Methylation frequencies of TP73, ARF, p15 (INK4B) , p16 (INK4A) , and RASSF1A were comparable in MGUS: 33%, 29%, 29%, 5%, and 0%, to that observed in MM: 45%, 29%, 32%, 7%, and 2%. All patients lacked methylation at p27 (KIP1) gene. In both entities, a concurrent methylation of p15 (INK4B) and TP73 was observed. The mean methylation index of MGUS was lower (0.16) than that of MM (0.24; p < 0.05). Correlations with clinicopathologic characteristics showed a higher mean age in MGUS patients with SOCS-1 methylated (p < 0.001); meanwhile in MM, methylation of p15 (INK4B) was more frequent in males (p = 0.009) and IgG isotype (p = 0.038). Our findings suggest methylation of TP73, ARF, p15 (INK4B) , and p16 (INK4A) as early events in the pathogenesis and development of plasma cell disorders; meanwhile, SOCS-1 methylation would be an important step in the clonal evolution from MGUS to MM.