The painting above shows light chain proximal tubulopathy with crystals, which is one type of a monoclonal gammopathy of renal significance (MGRS). MGRS, as defined by the International Kidney and Monoclonal Gammopathy Research Group, is a “clonal proliferative disorder that produces a nephrotoxic monoclonal immunoglobulin” (Leung N et al, 2019), and indicates end-organ damage resulting from a monoclonal gammopathy. The most common MGRS manifestations include AL amyloidosis, monoclonal immunoglobulin deposition disease, light chain cast nephropathy, and light chain proximal tubulopathy. In light chain proximal tubulopathy, a nephrotoxic monoclonal light chain induces acute tubular injury or proximal tubular dysfunction. Proximal tubular...