Untangling the tauopathies: Current concepts of tau pathology and neurodegeneration.

Tau is the most common misfolded protein responsible for human neurodegenerative diseases. The identification of mutations in MAPT, the gene that encodes tau, causing dementia and parkinsonism established the notion that tau aggregation is responsible for the development of disease. An increased understanding of the pathway leading from conformational changes in tau protein and tau propagation to neuronal dysfunction, cell death and clinical manifestation will be the key for the development mechanism-based therapeutic strategies for tauopathies.

J. Clifford Richardson and 50 years of progressive supranuclear palsy.

OBJECTIVE: To trace the historical events leading to Richardson's clinical description of progressive supranuclear palsy (PSP) in the context of subsequent observations of its clinical heterogeneity and pathologic overlap with other tauopathies. BACKGROUND: Fifty years ago, Canadian neurologist J. Clifford Richardson identified patients in Toronto with a syndrome of supranuclear vertical gaze palsy, pseudobulbar palsy, axial rigidity-in-extension, and cognitive impairment. In his seminal description, Richardson predicted that further clinicopathologic observations would broaden the clinical syndrome and that this was unlikely to be a disorder restricted to the Toronto region. METHODS: The recollections of two of Richardson's contemporaries and archival material from his time were used as primary materials. Publications that follow the evolution of his observations were examined. RESULTS: Recent factor analysis of pathologically verified PSP cases has confirmed the accuracy and uniformity of the original classic clinical description of PSP and vindicated Richardson's prediction of clinical variants. Most notably, a presentation with Parkinson syndrome and absent gaze palsy has been identified, with less severe PSP-tau pathology. CONCLUSIONS: In recognition of his seminal observations, we propose that the classic clinical presentation of PSP-tau pathology be renamed Richardson's disease, and that the commonest clinical variant be termed PSP-parkinsonism.

Tauopathies: recent insights into old diseases.

Neurofibrillary tangles are brain lesions that have been discovered at the beginning of the 20th century, using histological silver staining. Tangles are intra-neuronal hallmarks of a degenerating process: neurofibrillary degeneration (NFD). The basic component involved in tangle formation is tau protein. Tangles are found in more than 20 different neurodegenerative disorders, suggesting that NFD is a unique consequence to different types of etiological factors. However, tangles have a morphological and biochemical signature which is disease-specific. They are made up of different types of filaments such as paired helical filaments (PHFs) in Alzheimer's disease or straight filaments in progressive supranuclear palsy. Tau aggregates have a disease-specific biochemical bar-code due to the aggregation of specific sets of tau isoforms. Tau lesions have also a disease-specific pattern of spatio-temporal progression in the human brain which is well correlated to cognitive impairment. At last, pathological tau mutations are at the origin of familial fronto-temporal diseases with parkinsonism (FTDP-17). Together, these observations have generated the concept of tauopathies. Indeed, each tauopathy is defined by a combination of clinical, neuropathological, biochemical and genetic features. Most of them have a specific defect on tau (mutation, aberrant splicing, abnormal phosphorylation, abnormal processing, neuronal or genotypic vulnerability), suggesting that, in fact, the etiology of most tauopathies is directly linked to tau dysfunction. In conclusion, we observe that most dementing disorders are tauopathies and that most demented patients have a tauopathy.