Synthesis of abnormal heavy and light chains in multiple myeloma with visceral deposition of monoclonal immunoglobulin.

In a patient treated for IgA kappa myeloma, bone marrow relapse and a sharp drop in the serum IgA level paralleled tissue deposition of non-amyloid material reactive with anti-kappa anti-alpha sera in immunofluorescence studies of kidney and liver biopsies. Clinical manifestations were progressive renal failure with nephrotic syndrome, with both tubular and glomerular lesions (including nodular glomerulosclerosis), hepatomegaly, cardiac and neurological symptoms. Biosynthesis experiments showed the production of alpha chains diminished in length by about one domain which were rapidly degraded predominantly after secretion and of two species of light chains; normal-sized light chains which assembled with alpha chains and abnormally short ones which were secreted as free light chains. The apparent molecular weight of the light chains was larger in secretions than in cytoplasmic extracts, suggesting their glycosylation. These results suggest a causal relationship between tissue deposition and production of abnormal immunoglobulins by a variant clone, the emergence of which was possibly induced by Melphalan therapy.