Trans-suppression of misfolding in an amyloid disease.

The transthyretin (TTR) amyloid diseases, representative of numerous misfolding disorders, are of considerable interest because there are mutations that cause or suppress disease. The Val30 --> Met30 (V30M) TTR mutation is the most prevalent cause of familial amyloid polyneuropathy in heterozygotes, whereas a Thr119 --> Met119 (T119M) mutation on the second TTR allele protects V30M carriers from disease. Here, we show that the incorporation of one or more T119M TTR subunits into a predominantly V30M tetramer strongly stabilized the mixed tetramer against dissociation. Dissociation is required for amyloid formation, so these findings provide a molecular explanation for intragenic trans-suppression of amyloidosis. The data also suggest a potential therapeutic strategy, provide insight into tissue-specific deposition and amyloid composition, and support the validity of the amyloid hypothesis in human disease.