Behavioural variant frontotemporal dementia--defining genetic and pathological subtypes.

Behavioural variant frontotemporal dementia (bvFTD) is a clinically, genetically and pathologically heterogeneous neurodegenerative disorder caused by FTLD-tau, FTLD-TDP and FTLD-FUS pathologies. Clinically, patients present with behavioural symptoms that may include one or more of disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative, stereotyped and compulsive/ritualistic behaviour or hyperorality/dietary changes. Cognitive deficits, particularly executive dysfunction, are also seen. Neuroanatomically, patients have frontal and/or temporal lobe atrophy on neuroimaging. However, there is currently no clear correlation between the clinical and neuroanatomical phenotype in life and the underlying pathogenetics. With the advent of clinical trials in bvFTD, establishing the underlying pathology accurately during life will become increasingly important. This review therefore investigates current and future biomarkers that may help make a pathological diagnosis in life, i.e. bvFTD-tau, bvFTD-TDP and bvFTD-FUS, including clinical and neuropsychological data, neuroimaging, blood and CSF markers.