[Classification of amyloidosis]

Amyloidoses are a group of protein conformational diseases in which soluble precursor proteins form insoluble amyloid fibrils in the extracellular space. Amyloidoses are roughly classified in terms of their localized or systemic deposition, and are further grouped based on the types of precursor proteins. As of today, 27 different proteins have been recognized as amyloid precursor proteins. Amyloidoses are diagnosed by histopathological analysis using Congo red staining and/or electron microscopy, and the disease classification is made based on immunohistochemistry, proteomics, and gene analyses. The four main types of systemic amyloidosis are light-chain amyloidosis, reactive amyloid A amyloidosis due to chronic inflammatory diseases, β2-microglobulin amyloidosis associated with long-term hemodialysis, and hereditary transthyretin-related amyloidosis caused by mutations in the transthyretin gene. There are a many types of localized amyloidosis including cerebral endocrine, and cutaneous amyloidosis. In recent years, the treatment strategies for amyloidoses have greatly improved, and several forms of these are now treatable. Therefore, it is increasingly important to make an early diagnosis and begin treatment at the earliest, based on the precise disease classification of amyloidoses.