Proteins forming amyloids in diseases
To date, 37 human proteins have been found to form amyloid in pathology and be associated with well-defined diseases. The International Society of Amyloidosis classifies amyloid fibrils and their associated diseases based upon associated proteins (for example ATTR is the group of diseases and associated fibrils formed by TTR). A table is included below. Non-disease and functional amyloids
Many examples of non-pathological amyloid with a well-defined physiological role have been identified in various organisms, including human. These may be termed as functional or physiological or native amyloid. Functional amyloid in Homo sapiens:
Intralumenal domain of melanocyte protein PMEL
Peptide/protein hormones stored as amyloids within endocrine secretory granules
Receptor-interacting serine/threonine-protein kinase 1/3 (RIP1/RIP3)
Fragments of prostatic acid phosphatase and semenogelinsFunctional amyloid in other organisms:
Curli fibrils produced by E. coli, Salmonella, and a few other members of the Enterobacteriales (Csg). The genetic elements (operons) encoding the curli system are phylogenetic widespread and can be found in at least four bacterial phyla. This suggest that many more bacteria may express curli fibrils. GvpA, forming the walls of particular Gas vesicles, i.e. the buoyancy organelles of aquatic archaea and eubacteria
Fap fibrils in various species of Pseudomonas
Chaplins from Streptomyces coelicolor
Spidroin from Trichonephila edulis (spider) (Spider silk)
Hydrophobins from Neurospora crassa and other fungi
Fungal cell adhesion proteins forming cell surface amyloid regions with greatly increased binding strength
Environmental biofilms according to staining with amyloid specific dyes and antibodies. Tubular sheaths encasing Methanosaeta thermophila filamentsFunctional amyloid acting as prions
Several yeast prions are based on an infectious amyloid, e.g.
Pelizaeus–Merzbacher disease is an X-linked neurological disorder that damages oligodendrocytes in the central nervous system. It is caused by mutations in proteolipid protein 1 (PLP1), a major myelin protein. It is characterized by a decrease in the amount of insulating myelin surrounding the nerves (hypomyelination) and belongs to a group of genetic diseases referred to as leukodystrophies. Signs and symptoms
The hallmark signs and symptoms of Pelizaeus–Merzbacher disease include little or no movement in the arms or legs, respiratory difficulties, and characteristic horizontal movements of the eyes left to right.The onset of Pelizaeus–Merzbacher disease is usually in early infancy. The most characteristic early signs are nystagmus (rapid, involuntary, rhythmic motion of the eyes) and low muscle tone. Motor abilities are delayed or never acquired, mostly depending upon the severity of the mutation. Most children with Pelizaeus–Merzbacher disease learn to understand language, and usually have some speech. Other signs may include tremor, lack of coordination,  involuntary movements, weakness, unsteady gait, and over time, spasticity in legs and arms. Muscle contractures often occur over time. Mental functions may deteriorate. Some patients may have convulsions and skeletal deformation, such as scoliosis, resulting from abnormal muscular stress on bones. Cause
Pelizaeus–Merzbacher disease is caused by X-linked recessive mutations in the major myelin protein proteolipid protein 1 (PLP1). This causes hypomyelination in the central nervous system and severe neurological disease. The majority of mutations result in duplications of the entire PLP1 gene.