The reduced expression of proximal tubular transporters in acquired Fanconi syndrome with κ light chain deposition.

In a case of acquired Fanconi syndrome associated with smoldering myeloma, we confirmed the deposition of protease-resistant κ light chain proteins in a proximal tubular injury and found the decreased expression of apical tubular transporters including sodium glucose co-transporter, sodium phosphate co-transporter, uric acid transporter 1, and a decrease of Na(+)/K(+)-ATPase in the basolateral membrane. The protease-resistant kappa light chain has a pathological role in the expression of tubular transporters in the proximal tubule and causes Fanconi syndrome associated with smoldering myeloma.