AA protein in a case of "primary" or "idiopathic" amyloidosis.

Amyloidosis constitutes a group of diseases in which extracellular fibrils with a characteristic appearance are deposited in a variety of tissues. Several different proteins have been identified as the major subunits of the fibrils. In the primary and myeloma-associated type, the amyloid fibrils consist of immunoglobulin light chain fragments, whereas in the secondary type and the amyloid associated with familial Mediterranean fever the major component is the AA protein. In this report a 21 year old man of Yemenite extraction with no underlying disease and no family history of amyloidosis was found to have amyloid deposits composed of AA protein. Although clinically this might be classified as primary amyloidosis, the absence of light chain fragments makes that diagnosis unlikely. Therefore, it is suggested that whenever possible the clinical classification be supplemented by a description of the biochemical nature of the fibrils.