...Recently, some reports have indicated that BRCA1 dysfunction is involved in the pathogenesis of Alzheimer disease (AD). Furthermore, it has also been reported that BRCA1 accumulates within neurofibrillary tangles (NFTs) in the AD brain. In this study, we examined the immunohistochemical distribution of BRCA1 and another DDR protein, p53-Binding Protein 1 (53BP1), in AD, Pick disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration, and frontotemporal dementia with parkinsonism linked to chromosome 17. In control subjects, neither BRCA1 nor phosphorylated BRCA1 (pBRCA1; Ser1524) immunoreactivity was observed in neurons or glial cells; and that for pBRCA1 (Ser1423) and 53BP1 were slightly detected in neuronal nuclei. The immunoreactivity for both BRCA1 and pBRCA1 (Ser1423) was localized within phosphorylated tau inclusions in all tauopathies, whereas that for pBRCA1 (Ser1524) was mainly associated with Pick bodies in PiD and to a lesser extent with NFTs in AD. On the other hand, 53BP1-immunoreactive deposits tended to be increased in the nucleus of neurons in AD and PSP compared with those in control cases. Our results suggest that DDR dysfunction due to cytoplasmic sequestration of BRCA1 could be involved in the pathogenesis of tauopathies.