Nodular glomerulosclerosis associated with multiple myeloma. Role of light chain isoelectric point

A 68-year-old female patient with multiple myeloma exhibited advanced nodular glomerulosclerosis. Immunofluorescence of the kidney showed kappa light chain deposition in the mesangium and in glomerular and tubular basement membrane. Isoelectric focusing and immunofixation of urinary proteins revealed an isolated kappa light chain with an unusually high isoelectric point of 8.4. Most light chain proteins have isoelectric points in the 4.6 to 6.7 range. Since loss of fixed negative charges may precede experimental glomerulosclerosis, it is proposed that this cationic circulating kappa chain may have interacted with glomerular polyanion, thereby inducing a nodular sclerotic reaction leading to irreversible renal damage.