Background Mutations in tau have been found in a group of related disorders including the frontal lobe dementias, Aims To describe the clinical features and molecular pathology changes in a single case of a patient with frontal lobe dementia. Method A case report was compiled from neuropathological reports and genomic and gene expression analyses. Results A case with a splice-site mutation resulting in atypical frontotemporal clinical and neuropathological phenotype was found. Gene expression analysis suggests differential expression of isoforms of tau in regions in the brain. Conclusions Frontotemporal dementia can result from gene mutations that alter splicing and expression of tau. Declaration of interest This work was completed in the course of research funded by the Medical Research Council and the Wellcome Trust.