Acquired Fanconi syndrome

Acquired Fanconi syndrome occurs rarely. It may precede overt myeloma for years.46 49 Patients may have azotemia and various degrees of proteinuria, glycosuria, aminoaciduria, and phosphaturia. On renal biopsy, the damaged proximal tubular cells show atrophic changes and contain crystalline cytoplasmic inclusions without overt lesions of cast nephropathy. This syndrome is almost always associated with k light-chain proteinuria. Recent analysis of light chains in these patients showed a preferential involvement of Vk1 subgroup of limited germline origin. This light-chain V domain contains unusual hydrophobic sequences that are resistant to proteolysis by lysosomal cathepsin B. The accumulation of indigestible nephro-toxic light chains in proximal tubular cells provides a plausible explanation for the functional impairment.50

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