Transactive response DNA binding protein of 43 kDa (TDP-43) is considered to play an essential role in the pathogenesis of frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Growing body of evidence indicate that pathological TDP-43 inclusions frequently occur in the context of other distinctive hallmark pathologies, referred to as secondary

TDP-43 proteinopathies. Comorbid TDP-43 pathology is well-documented in several neurodegenerative disorders, including Alzheimer’s disease, Parkinson’s disease, multiple system atrophy, or progressive supranuclear palsy. It may also appear as a consequence of less obvious disease etiologies, i.e. post-traumatic (chronic traumatic encephalopathy), neoplastic (pilocytic astrocytoma), or post-infectious (post-encephalitic parkinsonism). The aim of the present review was to evaluate the incidence, morphology, and role of TDP-43 pathology in the secondary TDP-43 proteinopathies. This article (Part 1) discussed TDP-43 pathology in more common neurodegenerative diseases, including Alzheimer’s disease, Lewy body disease, Huntington’s disease, multiple system atrophy, corticobasal degeneration, and progressive supranuclear palsy. A follow-up article (Part 2) will describe abnormal TDP-43 changes in rare neurodegenerative diseases or neurological diseases with nondegenerative etiology.