You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Heavy chain disease and explain in detail?
Heavy chain disease is a form of paraproteinemia and plasma cell dyscrasia that involves the proliferation of cells producing immunoglobulin heavy chains.This disease is characterized by an excessive production of heavy chains that are short and truncated. These heavy chain disease proteins have various deletions, mainly in their amino-terminal part, which causes the heavy chains to lose the ability to form disulfide bonds with the light chains. The defect in the immunoglobulins presumably arises during somatic hypermutation. Deletion of the N-terminal part of the heavy chain disease protein leads to aggregation and signaling of the B cell receptor, presumably due to the loss of the anti-aggregating properties of the light chain.

Classification
There are four forms:

alpha chain disease (Seligmanns disease)
gamma chain disease (Franklins disease)
mu chain disease
delta chain disease

IgA/αHCD
The most common type of heavy chain disease is the IgA type, known as αHCD. The most common type of αHCD is the gastrointestinal form (known as immunoproliferative small intestine disease or IPSID), but it has also been reported in the respiratory tract, and other areas of the body.

IgG/γHCD
Franklins disease (gamma heavy chain disease)
It is a very rare B-cell lymphoplasma cell proliferative disorder which may be associated with autoimmune diseases and infection is a common characteristic of the disease