COMPLETE VARIABLE REGION DELETION IN A MU-HEAVY CHAIN DISEASE PROTEIN(ROUL) - CORRELATION WITH LIGHT-CHAIN SECRETION

In a patient affected with chronic lymphocytic leukemia with lymphocyt e surface mu and kappa determinants and vacuolated bone marrow plasma cells, the serum contained polymers of a truncated mu chain and normal -sized kappa chains. These light chains were present as monomers and c ovalent dimers in studies performed under dissociating conditions, but they were linked by non-covalent bridges to a portion of the serum sh ort mu chains. The patient's urine contained a kappa type Bence-Jones protein. Study of a messenger RNA and complementary DNA from blood cel ls showed the abnormal mu chain to lack the entire variable region, li kely due to a direct splicing of the leader peptide exon onto the CH1 exon. The production of light chains, a rare event in heavy chain dise ases, appears to correlate with the occurrence of a heavy chain deleti on restricted to the variable domain, likely because the non-covalentl y linked light chains allow these unusual heavy chains to be secreted.