Gamma heavy chain disease in a patient with rheumatoid arthritis – a laboratory evaluation

INTRODUCTION Heavy chain diseases (HCD) are neoplastic proliferations of B cells which secrete truncated immunoglobulin heavy chains without associated light chains. Being rare and probably underdiagnosed diseases the aim of this report is to show an additional case of gamma heavy chain disease in a 48 year old female patient with rheumatoid arthritis focusing on the laboratory presentation. MATERIALS AND METHODS Laboratory work-up included agarose gel electrophoresis (AGE), capillary zone electrophoresis (CZE), immunofixation and nephelometrically determined immunoglobulin and immunoglobulin subclasses of the patient's serum. Urine samples were also subjected to immunofixation and to a SDS-PAGE with consecutive immunoblot. RESULTS Nephelometrically measured elevated IgG concentrations were noted in combination with a decreased gamma globulin region and an increased beta globulin region on AGE. A definite monoclonal spike was not identified on AGE but at least suspected on CZE; finally serum and urine immunofixation demonstrated a monoclonal gamma heavy chain devoid of any corresponding light chains confirming the diagnosis of HCD. Analysis of the gamma heavy chain (HC) with means of SDS-PAGE revealed proteins of 40 kD and 80 kD most likely presenting a truncated HC in its monomeric and dimeric form and possibly leading to the failure of IgG-subclass typing with the applied IgG subclass antisera. CONCLUSION This case report illustrates a new case of gamma HCD demonstrating variable laboratory manifestations and therefore the need for heightened awareness concerning this disease when confronted with abnormal and discrepant protein profiles in routinely applied laboratory tests.