Amyloid nomenclature 2026: update, novel proteins, and discussion of intracellular aggregates and toxicity. Recommendations by the International Society of Amyloidosis Nomenclature Committee

Protein misfolding followed by aggregation into amyloid fibrils is a more common process than previously believed, and knowledge of the underlying mechanisms and their associations with disease is rapidly expanding. The International Society of Amyloidosis (ISA) has long maintained a Nomenclature Committee to meet the need for uniform terminology, amyloid protein names and abbreviations, and to harmonize these with other nomenclature systems. For this update, virtual meetings and electronic correspondence preceded the 2026 ISA meeting in Montevideo, Uruguay, resulting in the present revised document. Amyloid is defined by the beta-sheet structure of its principal fibril protein, although amyloid deposits formed in vivo contain additional components. The principles underlying the recommended amyloid nomenclature remain unchanged but have been further clarified. The number of known human amyloid fibril proteins associated with systemic amyloidosis remains 19. Most are linked to genetic variants and are extremely rare. In animals, nine different fibril proteins have been identified in association with systemic amyloidoses. The rapidly growing body of knowledge concerning pathological intracellular protein aggregates and their contribution to tissue vulnerability is covered in an expanded section of this paper.