SLC14A1 and plasmacytoma: The κ and λ chains differ in amino acid sequence and disulfide position.[19] The gene encoding κ chains is composed of the Vκ, Jκ, and Cκ gene clusters.[20] Under physiological conditions, the ratio of κ and λ free light chains in the serum equals 0.26 to 1.65.[21] The κ:λ ratio is altered in conditions associated with the monoclonal proliferation of plasma cells, such as plasmacytoma, and can be used for diagnosis and prognostication.