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heavy chain diseases (HCDs) are rare B-cell malignancies characterized
by the production of a monoclonal immunoglobulin heavy chain without an
associated light chain. There are three types of HCD, defined by the
class of immunoglobulin heavy chain produced: IgA (α-HCD), IgG (γ-HCD),
and IgM (μ-HCD). Alpha-HCD is the most common and usually occurs as
intestinal malabsorption in a young adult from a country of the
Mediterranean area. Gamma- and μ-HCDs are rarer and associated with a
B-cell non-Hodgkin lymphoma that produces an abnormal Ig heavy chain.
These patients may occasionally be diagnosed with a monoclonal
gammopathy of undetermined significance (MGUS). Fanconi syndrome, on
the other hand, can be primary (inherited) or secondary (acquired). The
only exception to this rule is the idiopathic form. Adult acquired
Fanconi syndrome can be a rare complication of a monoclonal gammopathy.
At diagnosis, most patients have an MGUS or smoldering multiple
myeloma, with renal failure and evidence of osteomalacia. During
follow-up, patients can develop an end-stage renal disease.
Chemotherapy provides little benefit on renal function.
|Table 1. Clinicopathologic features of heavy chain disease.|
|Figure 1. Clinicopathologic features in a case of IPSID with α-HCD. A) Immunofixation and B) immunoelectrophoresis positivity for the anti-IgA antiserum; C) plasma cells and marginal zone cells express monoclonal cytoplasmic α-chain at immunofluorescence; D) Radiologic studies of the gastrointestinal apparatus showing diameter alterations (dilations and strictures); E), F) and G) histological features of intestinal infiltration by α-HCD cells (10X, 20X and 100X respectively).|
|Table 2. Immunophenotypic characteristics of HCD cells.|
Myeloma-Associated Fanconi Syndrome (MAFS)