Amyloidosis: clinical picture, immunological and biomolecular features, treatment prospects

Amyloidosis is the name given to a group of clinically protean diseases whose common feature is the tissue accumulation of amyloid fibrils which have specific optical and staining properties, and are both insoluble in physiological solvents and resistant to proteolytic enzymes. Fibril deposition and progressive extracellular infiltration eventually result in atrophy due to compression. The structure of these fibrils embraces a wide range: immunoglobulin light chain or their fragments, acute phase proteins, hormones, protease inhibitors, beta 2-microglobulin, natriuretic peptides, and proteins whose function is still unknown. Despite this heterogeneity, however, they share a common crystallographic beta-pleated sheet structure. The clinical spectrum includes apparently primary forms, amyloidosis of myeloma, forms secondary to familial Mediterranean fever, Alzheimer's disease, forms associated with type 2 diabetes or medullary carcinoma of the thyroid, inherited-familial amyloidosis, and other less common conditions. Two pathogenetic phases are involved: enhanced production of precursor proteins and their abnormal enzyme cleavage, resulting in the formation of intermediate products corresponding to the amyloid fibrils. The results of treatment are still disappointing: alkylating agents and/or cortico-steroids are used in primary forms and for amyloidosis of myeloma; colchicine in familial Mediterranean fever; DMSO in renal amyloidosis; plasmapheresis in inherited-familial forms, together with the supportive management obviously dictated by clinical manifestations.