The systemic amyloidoses.

PURPOSE OF REVIEW: Clinical management of the amyloidoses has historically been the province of rheumatologists, because of the relation to long-standing inflammation in rheumatoid arthritis, ankylosing spondylitis, and juvenile chronic arthritis. Currently, nephrologists, hematologist-oncologists, neurologists, and transplant surgeons all have a diagnostic or therapeutic interest. Current advances, using the tools of physical biochemistry, cell biology, and genetics, have begun to impact the diagnosis and clinical management of these disorders and raise questions regarding our notions of protein conformation in vivo and how nonnatively folded proteins may produce disease.

RECENT FINDINGS: It appears that all amyloidogenic precursors undergo some degree of misfolding that allows them to populate an immediate precursor pool from which they rapidly aggregate. Depending on the particular protein, a variety of mechanisms appear operative, some of which involve nonphysiologic proteolysis, defective physiologic proteolysis, mutations involving changes in thermodynamic or kinetic properties, and pathways that are yet to be defined. Whatever the particular process, the result is a tendency toward oligomeric aggregation followed by the assembly of higher order structures that become insoluble under physiologic conditions. Detailed analyses have been described for transthyretin (senile systemic amyloidosis and familial amyloid polyneuropathy), immunoglobulin light chains (light-chain amyloid), beta2 microglobulin (dialysis-related amyloid), and apolipoprotein A1, and are in process for others. SUMMARY Therapies have been proposed based on precursor stabilization (transthyretin), elimination of the synthesizing cell (light-chain amyloid), fibril disruption and immunization to induce host-mediated aggregate clearance (Alzheimer disease, light-chain amyloid, prions), and aggressive therapy of a primary inflammatory process (amyloid A). During the next decade, the value of these therapies, and others, suggested by studies on the basic properties of cells and proteins, will become clear.