TARDBP and Alzheimer disease: Although the majority of semantic dementia cases have TDP-43 pathology, a small minority of cases may arise from tauopathies, most often Alzheimer’s disease pathology or Pick’s disease pathology.15 16 31 In keeping with this, 25 of 34 patients clinically diagnosed with semantic dementia (or svPPA) and in the Cambridge Brain Bank are positive for ubiquitin or TDP-43 and negative for both tau and beta-amyloid.