Once negative results are obtained for HTT, C9orf72 and TBP expansions, the diagnostic rate in patients with HDPC plummets.4 14 15 Our data suggests that novel, unusual variants in dementia genes could confer atypical features, expand the phenotypic spectrum of dementias, and further elucidate the mechanisms at work in subcortical dementias. The gene discussed is C9orf72; the disease is dementia.