Monoclonal gammopathy of renal significance (MGRS): the characteristics and significance of a new meta-entity.

Monoclonal gammopathy of renal significance (MGRS) is a new nosological group of entities (meta-entity) defined in 2012, whose pathogenesis depends on monoclonal immunoglobulins (Ig) secreted by low-grade lymphoproliferative disorders, which belong to M-protein-related diseases. Renal damage is the result of monoclonal Ig deposit or its activity as autoantibodies, which can compromise any nephronal area. MGRS does not include kidney diseases produced by high-grade lymphoproliferative disorders as well as those whose pathogenesis are independent of monoclonal Ig (such as drug toxicity or metabolic disorders). The importance of this hemato-nephrological meta-entity is based on two aspects: First, it is associated with increased morbidity and mortality, including recurrence in post-renal transplant or its appearance as "de novo" after it; and second, it usually improves after treating the plasmocyte or lymphocyte clone responsible, leading to the elimination of M-protein. Between low-grade lymphoproliferative disorders, monoclonal gammopathy of undetermined significance (MGUS) requires special consideration for two reasons: First, it is the disorder most related to MGRS; second, when MGUS progresses to MGRS, effective treatment against toxic underline clone should be performed taking into account the nephrological perspective.