GRN Thr272fs clinical heterogeneity: a case with atypical late onset presenting with a dementia with Lewy bodies phenotype.

We describe a case of late onset frontotemporal dementia carrying the g. 1977 1980 delCACT (Thr272fs) mutation in progranulin (GRN) gene, characterized by a positive family history for dementia and a clinical phenotype resembling dementia with Lewy bodies. Symptoms included prominent visuospatial impairment, complex misidentification syndrome, visual zooptic hallucinations, hypersomnia, mental fluctuations, and signs of parkinsonism. The patient showed normal cerebrospinal fluid levels of amyloid-beta, tau, and Ptau biomarkers, an asymmetric pattern of cerebral atrophy and hypoperfusion, and parietal hypometabolism. A major contributing factor to the diagnosis was the testing of plasmatic progranulin levels (extremely low), which prompted us to sequence GRN.