An update of clinical, pathologic, and biochemical aspects of amyloidosis

A role for destabilizing amino acid replacements in light-chain amyloidosis

Light-chain (L-chain) amyloidosis is characterized by deposition of fibrillar aggregates composed of the N-terminal L-chain variable region (VL) domain of an immunoglobulin, generally in individuals overproducing a monoclonal L chain. In addition to proteolytic fragmentation and high protein concentration, particular amino acid substitutions may also contribute to the tendency of an L chain to aggregate in L-chain amyloidosis, although evidence in support of this has been limited and difficult to interpret. In this paper we identify particular amino acid replacements at specific positions in the VL domain that are occupied at frequencies significantly higher in those L chains associated with amyloidosis. Analysis of the structural model for the VL domain of the Bence-Jones protein REI suggests that these positions play important roles in maintaining domain structure and stability. Using an Escherichia coli expression system, we prepared single-point mutants of REI VL incorporating amyloid-associated amino acid replacements that are both rare and located at structurally important positions. These mutants support ordered aggregate formation in an in vitro L-chain fibril formation model in which wild-type REI VL remains soluble. Moreover, the ability of these sequences to aggregate in vitro correlates well with the extent to which domain stability is decreased in denaturant-induced unfolding. The results are consistent with a mechanism for the disease process in which the VL domain, either before or after proteolytic cleavage from the L-chain constant region domain, unfolds by virtue of one or more destabilizing amino acid replacements to generate an aggregation-prone nonnative state.

Electronmicroscopic observation of amyloid deposits in the vascular walls of the choroid plexus in systemic amyloidosis

This report concerns an ultrastructural study of the vessels of the choroid plexus in 3 cases of systemic amyloidosis, sections of formalin-fixed brains being used. Small-sized arteries and arterioles were mainly affected by deposition of amyloid fibrils. In the arterioles, the amyloid fibrils were often so densely accumulated that they separated individual smooth muscle cells of the media and reached the subendothelial region. The basal surface of the endothelium of such vessels showed frequent invaginations filled with amyloid tufts; some of the tufts displaced the thin cytoplasm of the endothelial cells toward the lumen. Occasionally, tufts of amyloid fibrils were found to be exposed to and to float in the vascular lumen. These observations were made only in severely amyloid-laden vessels. Among the several possibilities regarding the tuft-endothelial relationship, the transendothelial transport of amyloid tufts is most likely, but the possibility of intraendothelial processing of amyloid precursor proteins and their secretion to form fibrils extracellularly cannot be excluded.

Renal amyloidosis characterized by abnormally thick fibrils

A renal biopsy of a 57-year-old man with nephrotic syndrome revealed marked glomerular deposition of Congo red-positive, bire-fringent material characteristic for amyloid. Ultrastructurally, however, this material is composed of nonbranching, haphazardly arranged fibrils of approximately three times the thickness of typical amyloid fibrils. To our knowledge, there has been no report of such a finding, and this unique case enlarges the morphologic spectrum of renal fibrillosis.

Nephrotic syndrome and primary tubular amyloidosis in a child: a case report

Nephrotic syndrome in a 19-month-old child was associated with an unusual form of primary renal amyloidosis. The amyloid deposit was in the tubulo-interstitium and not in the glomeruli. Although the deposit did not stain with Congo red, it had the ultrastructural characteristics of amyloid. The patient had resistant nephrotic syndrome, and he subsequently developed microhaematuria and glucosuria.

Pathological Society of Great Britain and Ireland. 154th meeting, 7-9 January 1987. Synopses of papers

The transformation of serum proteins into Congo red-sensitive fibrillar material is requisite for the onset and progression of amyloid disease. All the mechanisms which lead to the disease itself have not been elucidated, but our knowledge has increased significantly. It is apparent that in all types of amyloid fibrils, three common features are displayed by the major protein constituents. These are that the fibril protein has a serum precursor, a high degree of anti-parallel beta-sheet conformation and a distinctive ultrastructure on electron microscopy. In the AL and AA forms of amyloidosis, the putative precursors appear to undergo limited degradation to form the protein component of amyloid fibrils. It has been suggested that there may be certain primary structural characteristics inherent in precursor molecules which make them amyloidogenic, thus predisposing them to amyloid fibril formation. This would include certain subtypes of immunoglobulin light chains, possibly kappa I and lambda VI, in the AL type of amyloidosis and one of the polymorphic SAA species, SAA2, which has been identified as the predominating isotype found in AA amyloid fibrils. In AH amyloidosis, the mechanism of amyloid fibril formation appears to be simply a concentration phenomenon where elevated concentrations of B2-M are not handled normally and amyloid deposition is the result. Amyloidogenesis in the hereditary form of systemic amyloidosis may involve other factors in addition to the presence of a variant precursor prealbumin as indicated by the delayed onset of the disease. It is evident that the elucidation of the mechanism(s) which governs the onset and progression of the amyloidoses will allow future regulation and treatment of these all too often complex disorders.

Amyloidosis secondary to juvenile rheumatoid arthritis: a case report from Saudi Arabia

A case of histologically documented renal amyloidosis occurring in a boy who had juvenile rheumatoid arthritis is presented. The presenting problem was massive proteinuria resulting in nephrotic syndrome. Secondary amyloidosis is a serious complication of juvenile rheumatoid arthritis and it indicates very poor prognosis.

Nodular primary localized cutaneous amyloidosis: immunohistochemical evaluation and treatment with the carbon dioxide laser

Nodular primary localized cutaneous amyloidosis is an uncommon disorder for which there is no consistently satisfactory treatment. The amyloid fibrils are thought to have an immunoglobulin light chain derivation and systemic involvement must be excluded in all cases. We report a patient with a large scalp lesion of nodular primary localized cutaneous amyloidosis whose immunohistochemical evaluation revealed lambda light chain deposits and who thus far has no apparent systemic involvement. The lesion was treated by the carbon dioxide (CO2) laser with excellent cosmetic results and minimal morbidity.

Immunocytochemical demonstration of prealbumin in the vitreous in heredofamilial amyloidosis

Vitreous material obtained at pars plana vitrectomy from a patient with heredofamilial amyloidosis with vitreous involvement and control vitreous from a patient without amyloidosis were subjected to immunocytochemical studies. P component (AP), a minor constituent of all amyloid deposits, was found in trace amounts in the familial amyloid vitreous, but other amyloid proteins, which occur in secondary amyloidosis or in primary amyloidosis, were not found. The major amyloid protein in the vitreous in heredofamilial amyloidosis (but not control vitreous) was found to be prealbumin.