Tauopathy
Tauopathy belongs to a class of neurodegenerative diseases involving the aggregation of tau protein into neurofibrillary or gliofibrillary tangles (Neurofibrillary tangle) in the human brain. Tangles are formed by hyperphosphorylation of the microtubule protein known as tau, causing the protein to dissociate from microtubules and form insoluble aggregates. (These aggregations are also called paired helical filaments.) The mechanism of tangle formation is not well understood, and whether tangles are a primary cause of Alzheimers disease or play a peripheral role is unknown.

Detection and imaging
Post-mortem
Tau tangles are seen microscopically in stained brain samples.Pre-mortem
In living patients tau tangle locations can be imaged with a PET scan using a suitable radio-emissive agent.

Alzheimers disease
Neurofibrillary tangles were first described by Alois Alzheimer in one of his patients with Alzheimers disease (AD). The tangles are  considered a secondary tauopathy. AD is also classified as an amyloidosis because of the presence of senile plaques.When tau becomes hyperphosphorylated, the protein dissociates from the microtubules in axons. Then, tau becomes misfolded and the protein begins to aggregate, which eventually forms the neurofibrillary tangles seen in Alzheimers patients. Microtubules also destabilize when tau is dissociated. The combination of the neurofibrillary tangles and destabilized microtubules result in disruption of processes such as axonal transport and neural communication.The degree of NFT involvement in AD is defined by Braak stages. Braak stages I and II are used when NFT involvement is confined mainly to the transentorhinal region of the brain, stages III and IV when theres also involvement of limbic regions such as the hippocampus, and V and VI when theres extensive neocortical involvement. This should not be confused with the degree of senile plaque involvement, which progresses differently.

Other diseases
Primary age-related tauopathy (PART) dementia, with NFTs similar to AD, but without amyloid plaques.
Chronic traumatic encephalopathy (CTE)
Progressive supranuclear palsy (PSP)
Corticobasal degeneration (CBD)
Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17)
Vacuolar tauopathy
Lytico-bodig disease (Parkinson-dementia complex of Guam)
Ganglioglioma and gangliocytoma
Meningioangiomatosis
Postencephalitic parkinsonism
Subacute sclerosing panencephalitis (SSPE)
As well as lead encephalopathy, tuberous sclerosis, Pantothenate kinase-associated neurodegeneration, and lipofuscinosisIn both Picks disease and corticobasal degeneration, tau proteins are deposited as inclusion bodies within swollen or "ballooned" neurons.Argyrophilic grain disease (AGD), another type of dementia, is marked by an abundance of argyrophilic grains and coiled bodies upon microscopic examination of brain tissue.  Some consider it to be a type of Alzheimers disease. It may co-exist with other tauopathies such as progressive supranuclear palsy and corticobasal degeneration, and also Picks disease.Tauopathies are often overlapped with synucleinopathies, possibly due to interaction between the synuclein and tau proteins.The non-Alzheimers tauopathies are sometimes grouped together as "Picks complex" due to their association with frontotemporal dementia, or frontotemporal lobar degeneration.

See also
Proteopathy

References


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