Structure of ATTRv-F64S fibrils isolated from skin tissue of a living patient

Article https://doi.org/10.1038/s41467-025-67457-2 Structure of ATTRv-F64S fibrils isolated from skin tissue of a living patient Received: 18 July 2025 Accepted: 25 November 2025 1234567890():,; 1234567890():,; Check for updates Jun Yu 1,4, Xuefeng Zhang 1,4, Sandra Pinton2, Elena Vacchi Andrea Cavalli 3, Matteo Pecoraro 3, Giorgia Melli 2 & Andreas Boland 1 2 , Amyloid transthyretin-derived (ATTR) amyloidosis is a degenerative, systemic disease characterized by transthyretin fibril deposition in organs like the heart, kidneys, liver, and skin. In this study, we report the cryo-EM structure of transthyretin fibrils isolated from skin tissue of a living patient carrying a rare genetic mutation (ATTRv F64S). The structure adopts a highly conserved fold previously observed in other ATTR fibrils from various tissues or different genetic variants. Mass spectrometry was used to evaluate fibril content and to identify common post-translational modifications. The structural consistency between ATTR filaments from different tissues or patients validates noninvasive skin biopsy as a diagnostic tool. Amyloid transthyretin-derived (ATTR) amyloidosis is one of the most prevalent forms of systemic amyloidosis and encompasses two types: a genetic (ATTRv) and a sporadic wild-type (ATTRwt) form. ATTRv amyloidosis arises from pathological mutations in the TTR gene, including amino acid substitutions, duplications, and deletions1. Transthyretin (TTR) mutations often destabilize the native TTR fold, leading to amyloid formation in multiple organs such as the heart, kidneys, liver or skin1,2. To date, a total of 216 mutations have been identified, including 200 amyloidogenic and 16 non-amyloidogenic mutations1,3. The clinical manifestations of hereditary ATTRv amyloidosis are highly variable, however, the predominant forms are characterized by peripheral polyneuropathy and an early-onset disease4. In contrast, ATTRwt amyloidosis is associated with agingrelated factors or unknown processes that lead to the extracellular deposition of ATTR fibrils in tissues5, and late-onset cardiomyopathy is typical6. Based on their composition and morphology, ATTR fibrils are classified into two main types. Type A fibrils are composed of fulllength (127 amino acids) or fragmented TTR molecules and can be found in ATTRwt and most ATTRv variants. In contrast, type B fibrils only contain full-length TTR7,8. Importantly, different fibril types are associated with specific diseases in neurodegenerative pathologies9. In addition to genetic mutations, post-translational modifications (PTMs) can influence the formation and characteristics of amyloid fibrils. PTMs have been implicated in altered behaviour of many amyloid proteins, including amyloid β, tau, α-synuclein, huntingtin, and TDP4310. Several types of modification, including phosphorylation11, acetylation12 and ubiquitination13 have been described as modulators of aggregation rate or extent, aggregate stability, and cytotoxicity. A growing number of cryo-EM structures of ATTR fibrils, extracted from post-mortem tissues such as the heart, eyes and nerves provided critical insights into the structural organisation of ATTR amyloid fibrils14–22. All structures share a common, relatively compact and β-sheet-rich fold that has been described as spearhead-shaped14. Despite their overall structural homogeneity, ATTR fibrils from different tissues exhibit local variations in a region that spans amino acids G57 to G6719, referred to as ‘gate’ region. For example, in cardiac fibrils of ATTRv-I84S patients four distinct gate states have been observed, named open, closed, broken and absent. In contrast, in ATTRv-V30M fibrils from the eye only one gate type was observed, called blocking gate15,19. ATTRwt cardiac fibrils from five patients and ATTRv fibrils (V20I, P24S, V30M, G47E, T60A, V122I and V122Δ) from various tissues show a closed gate near a polar channel. Polymorphism has also been observed in the number of protofilaments. Most ATTR fibrils consist of a single protofilament under cryo-EM conditions, with the exceptions of ATTRv-V122Δ cardiac fibrils that contain one or two protofilaments 1 Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland. 2Institute for Translational Research (IRT), Faculty of Biomedical Sciences, Università della Svizzera italiana (USI) and Ente Ospedaliero Cantonale (EOC), Bellinzona, Switzerland. 3Institute for Research in Biomedicine (IRB), e-mail: ; Università della Svizzera Italiana (USI), Bellinzona, Switzerland. 4These authors contributed equally: Jun Yu, Xuefeng Zhang. Nature Communications | (2026)17:781 1 Article and ATTRv-V30M fibrils from the eye that are formed by multiple protofilaments15,22. Recently, we showed that skin biopsy is an extremely sensitive, minimally invasive test for detecting and typing ATTR amyloidosis23. In this study, we use immunohistochemistry, mass spectrometry, and cryogenic electron microscopy (cryo-EM) to describe the molecular composition and the structural characteristics of amyloid fibrils extracted from ankle and thigh tissues from skin biopsies of a living ATTRv-F64S patient. The ATTR fibril structure of this genetic variant has not been determined yet. Our work reveals that ATTRv-F64S fibrils contain one protofilament and, less frequently, two protofilaments. The single protofilament adopts a near-identical fold to that of ATTRwt and most ATTRv fibrils, featuring a closed gate. Our structure of ATTR fibrils derived from a skin biopsy of a living patient demonstrates that sufficient quantities of amyloid fibrils can be extracted from minimal amount of skin tissue (between 5-10 milligrams). The structural conservation of ATTR fibrils across various tissues, including skin, further corroborates skin biopsy as a minimally invasive test for detecting, typing and determining the structure of ATTR amyloid fibrils. Results Characterisation of ATTR fibrils from ankle and thigh skin biopsies of a living patient In a first step we quantified the abundance of ATTR amyloid fibrils in two different skin sections, namely from ankle and thigh tissue. Amyloid deposits were found in the subepidermal layers and dermis, primarily around arterioles and sweat glands, consistent with our previous report23. Filaments were stained with Congo red dye that results in red or pink deposits that can be observed by brightfield (BF) microscopy (Supplementary Fig. 1a, BF). Using polarized light (PL) the characteristic birefringence of amyloid fibrils was detected in both tissues (Supplementary Fig. 1a, PL). When comparing ankle and thigh tissue, a stronger Congo red staining and higher birefringence was detected in ankle tissue from this patient. PGP9.5 (Protein Gene Product 9.5) antibody staining showed reduced intraepidermal nerve fibre density in both samples, confirming small fibre neuropathy (Supplementary Fig. 1a, PGP9.5). We next extracted ATTR fibrils from ankle and thigh tissue obtained by skin biopsy. Fibril extractio (...truncated)