Frontotemporal lobar degeneration with ubiquitinated tau-negative inclusions and additional α-synuclein pathology but also unusual cerebellar ubiquitinated p62-positive, TDP-43-negative inclusions

Mutations in the progranulin (PGRN) gene on chromosome 17 have been shown to be responsible for one non-tauopathy subtype of familial frontotemporal lobar degeneration - frontotemporal lobar degeneration with ubiquitinated, tau-negative inclusions (FTLD-U). Such cases have pathological similarities to sporadic cases with neuronal inclusions positive for ubiquitin, the ubiquitin binding protein, p62 and the newly recognised protein TDP-43 but negative for hyperphosphorylated (HP) tau. There has been a recent report on two families with a novel progranulin mutation where the neuropathology showed not only TDP-43 neuronal positivity but separate tau and/or alpha-synuclein pathology. We describe an unusual case with some family history but no mutation in the progranulin gene. The pathological features were typical for FTLD-U but with additional significant alpha-synuclein pathology, and unusual ubiquitin-positive, p62-positive, TDP-43-negative inclusions in the cerebellum. This case may represent a further pathological phenotype for familial FTLD-U. It also highlights the need for further investigations on the ubiquitin binding protein p62 as a marker in FTLD-U. It is certainly possible that the presence or absence of these ubiquitinated p62-positive yet TDP-43-negative cerebellar inclusions may act as a useful correlative factor in the future.