The term alpha heavy chain disease (alpha HCD) has been extensively used in the literature, since many cases are initially recognized by the presence of an abnormal alpha chain in the serum. However, the term immunoproliferative small intestinal disease (IPSID) was adopted by the WHO in 1978 and will be used here. IPSID is a variant of extranodal marginal zone lymphoma of mucosa associated lymphoid tissue (MALT)in which defective alpha heavy chains are secreted; it is also discussed in the section on extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT)
. It occurs in young adults and involves the gastrointestinal tract, resulting in malabsorption and diarrhoea. IPSID begins as a process sometimes reversible by antibiotics but may progress to diffuse large B-cell lymphoma (DLBCL).