A rare monoclonalgammopathy characterized by renal proximal tubule dysfunction secondary to monoclonal kappa light chain deposits in proximal tubular cells. Clinical presentation is with variable chronic kidney disease, low molecular weight proteinuria, aminoaciduria, hyperphosphaturia, uricosuria, bicarbonaturia, and non-diabetic glycosuria. Renal phosphate and urate wasting may cause hypophosphatemia and hypouricaemia.