BACKGROUND: The amyloid fibril in hereditary transthyretin (TTR) Val30Met (pVal50Met) amyloid (ATTR Val30Met) amyloidosis is composed of either a mixture of full-length and TTR fragments (Type A) or of only full-length TTR (Type B). The type of amyloid fibril exerts an impact on the phenotype of the disease, and on the outcome of diagnostic procedures and therapy. The aim of the present study was to investigate if the type of amyloid fibril remains the same within ATTR Val30Met amyloidosis families.

METHODS: Fifteen families were identified in whom at least two first-degree relatives had their amyloid fibril composition determined. The type of ATTR was determined by Western blot in all but two patients. For these two patients a positive 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid scintigraphy indicated ATTR Type A.

RESULTS: In 14 of the 15 families, the same amyloid fibril composition was noted irrespective of differences in age at onset. In the one family, different ATTR fibril types was found in two brothers with similar ages at onset.

CONCLUSIONS: Family predisposition appears to have an impact on amyloid fibril composition in members of the family irrespective of their age at onset of disease, but if genetically determined, the gene/genes are likely to be situated at another location than the TTR gene in the genome.

Systemic AA amyloidosis is a worldwide occurring protein misfolding disease of humans and animals. It arises from the formation of amyloid fibrils from the acute phase protein serum amyloid A. Here, we report the purification and electron cryo-microscopy analysis of amyloid fibrils from a mouse and a human patient with systemic AA amyloidosis. The obtained resolutions are 3.0 angstrom and 2.7 angstrom for the murine and human fibril, respectively. The two fibrils differ in fundamental properties, such as presence of right-hand or left-hand twisted cross-beta sheets and overall fold of the fibril proteins. Yet, both proteins adopt highly similar beta-arch conformations within the N-terminal similar to 21 residues. Our data demonstrate the importance of the fibril protein N-terminus for the stability of the analyzed amyloid fibril morphologies and suggest strategies of combating this disease by interfering with specific fibril polymorphs.

ATTR amyloidosis is one of the worldwide most abundant forms of systemic amyloidosis. The disease is caused by the misfolding of transthyretin protein and the formation of amyloid deposits at different sites within the body. Here, we present a 2.97 angstrom cryo electron microscopy structure of a fibril purified from the tissue of a patient with hereditary Val30Met ATTR amyloidosis. The fibril consists of a single protofilament that is formed from an N-terminal and a C-terminal fragment of transthyretin. Our structure provides insights into the mechanism of misfolding and implies the formation of an early fibril state from unfolded transthyretin molecules, which upon proteolysis converts into mature ATTR amyloid fibrils.

For the first time, we report of a Swedish family of five individuals with a TTR Glu54Leu (p. Glu74Leu) mutation in the transthyretin gene. This mutation has been previously described a few times in the literature, but no phenotypic or clinical description has been done before. The most common mutation in the Swedish population is TTRVal30Met and is mostly found in the Northern part of Sweden. Interestingly, the TTRGlu54Leu mutation was found in the same endemic area. The main phenotype of the TTR Glu54Leu patients is severe cardiomyopathy, which resulted in heart transplantation for the index person. As previously seen for ATTR amyloidosis patients with mainly cardiomyopathy, the amyloid fibrils consisted of a mixture of full-length and fragmented TTR species. However, western blot analyses detected a previously unrecognized band, indicating that these patients may have a third, so far unrecognized, fibril composition type that is distinct from the usual type A band pattern.