Biochemical characterization of amyloid derived from the variable region of the kappa light chain subgroup III.

We report the clinical data and results of biochemical studies of amyloid in a postpartum patient. The amyloidosis was not associated with myeloma, and immunopathologic examination of the amyloid deposits gave inconclusive results. Biochemical analysis of the deposits proved that the amyloid protein JUN was derived from the variable region of the kappa light chain subgroup III and is homologous to a rarely expressed protein POM, which was previously shown to have rheumatoid factor activity. The significance of this association and the diagnostic problems associated with certain cases of amyloid derived from immunoglobulin light chain (type AL) are discussed.