Heavy chain diseases

Heavy chain diseases (HCDs) are rare B-cell lymphoplasma-cell proliferative disorders characterized by production of truncated monoclonal immunoglobulin heavy chains without associated light chains. HCDs involving the three main immunoglobulin classes have been described; α-HCD is the most common and has the most uniform presentation, γ- and μ-HCDs have variable clinical presentations and histopathologic features. HCDs can be thought of as variant types of non-Hodgkin lymphoma: α-HCD presents as an extranodal marginal-zone lymphoma of mucosa-associated lymph-node tissue, γ-HCD as lymphoplasmacytoid non-Hodgkin lymphoma, and μ-HCD as small lymphocytic non-Hodgkin lymphoma or chronic lymphocytic leukemia. Diagnosis of HCD requires documentation of a deleted immunoglobulin heavy chain without a bound light chain in the serum or urine. Prognosis is variable, and no standardized effective treatment programs are available except for α-HCD, which in its early stage may respond to antibiotics.