Neurodegenerative diseases are progressive, acquired brain disorders affecting a growing number of people as populations age. Clinically, these conditions can be distinguished by different symptoms, depending on the brain region affected. Biologically, these disorders are characterized by the aggregation of certain cerebral proteins, thus being called proteino- pathies. In Alzheimer’s disease, amyloid proteins aggregate without causing symptoms, though this promotes symptomatic tau protein aggregation that takes place in the mesiotemporal lobe, responsible for encoding new memory information. More rarely, in atypical Alzheimer’s disease, tauopathy can occur in other brain regions, inducing diverse symptoms. These atypical Alzheimer’s disease cannot be diagnosed clinically without biological confirmation.

Tau protein aggregation is a hallmark shared by other neurodegenerative diseases, collectively called tauopathies. Typically, tauopathy initially occurs in brain regions distinct from the mesiotemporal lobe, which occasionally resembles Alzheimer’s disease. Due to imperfect concordance between the pathology type and affected brain regions, the development of biological tools (=biomarkers) is most critical for clinical research in neurodegenerative diseases. Distinct etiological treatments may be required to cure these diseases, given that different diseases exhibit varied tau modifications leading to different aggregates upon histological analysis. Though Alzheimer’s disease can now be diagnosed in vivo based on cerebrospinal fluid analysis, this is not yet the case for other tauopathies.

Cerebral histological abnormalities have enabled the classification of tauopathies based on the observation of abnormal phosphorylated 3R or 4R tau protein aggregates (3R vs. 4R denomination corresponding to the type of tau protein isoform). In Alzheimer’s disease, all isoforms do aggregate, whereas in other tauopathies only one isoform type does. Nevertheless, the distinction of tauopathies based on the sole measurement of tau isoforms in cerebrospinal fluid remains elusive.

The article focuses on a biochemical study of the tau protein and its post-translational modifications. It paves the way for confirming the diagnosis of non-Alzheimer’s tauopathies during the patient’s lifetime, thereby establishing a biological diagnosis. This advancement provides a better clinical understanding of these diseases, their evolution, and prognosis, both for patients and their families. In terms of research, this approach should enable the inclusion of patients into therapeutic trials at an early disease stage. This breakthrough could also provide insights into the exact role of the tau protein, linking it with genetic advancements in these diseases, for diagnosis at a pre-clinical stage. Through this study, tauopathies are entering a new era, transitioning from a post-mortem clinical-histological classification to an in vivo clinical-biological classification.