Acquired monoclonal Ig light chain-associated Fanconi syndrome is a rare kidney disorder where abnormal monoclonal kappa light chains deposit in the cells of the renal proximal tubule. This deposition disrupts normal kidney function and can lead to a range of kidney-related problems. People with this condition may have chronic kidney issues and problems with the way their kidneys handle certain substances. The disorder specifically affects the kidney's ability to reabsorb various small proteins and other molecules, which can lead to the loss of important nutrients and electrolytes in urine.

The clinical presentation of this condition can vary. People with this condition may experience chronic kidney disease along with abnormal losses of small proteins and other substances in the urine. These include low molecular weight proteinuria, aminoaciduria, hyperphosphaturia, uricosuria, bicarbonaturia, and non-diabetic glycosuria. Loss of phosphate and urate can also lead to low levels in the blood.

This condition is caused by a monoclonal gammopathy, where a single type of immunoglobulin light chain, specifically kappa light chains, deposits in the proximal tubular cells of the kidney. These deposits lead to the dysfunction of the kidney's reabsorption processes. No genetic cause has been identified, and it is considered an acquired disorder.