Genetic prion diseases presenting as frontotemporal lobar degeneration: clinical features and diagnostic challenge

Abstract Background Elucidate the clinical and ancillary feature of genetic prion diseases (gPrDs) presenting with frontotemporal lobar degeneration (FTLD) in order to aid early identification, diagnosis, and referral for genotype testing. Method Global data of gPrDs presenting with FTLD caused by prion protein gene (PRNP) mutations were collected from literature review and our records. Fifty‐one cases of typical FTLD and 136 of prion diseases admitted to our institution were included as controls. Clinical and ancillary data of the different groups were compared. Result Forty‐nine cases of gPrDs presenting with FTLD were identified, 23 of which were female. Twenty‐three mutations in PRNP have been reported to be associated with the FTLD, with P39L being the most commonly reported, seen in 4 families with 5 cases. Compared to FTLD or prion diseases, gPrDs presenting with FTLD is characterized by earlier onset age (median: 45 vs. 61/60 years) and stronger family history (81.6% vs. 27.5/13.2%). In addition, gPrDs presenting with FTLD exhibited shorter duration (median: 5 vs. 8 years), and a higher rate of clinical and ancillary features of prion diseases compared to FTLD. Compared to prion diseases, gPrDs presenting with FTLD had a longer duration of symptoms (median: 5 vs. 1.1 years), higher rates of frontotemporal atrophy (89.7% vs. 3.3%), lower rates of periodic short‐wave complexes on EEG (0% vs. 29.4%), and hyperintensity on MRI (25.0% vs. 83.0%). The frequency of the Val allele for codon 129 in PRNP carriers with FTLD was significantly higher than that reported in literature for gPrDs (33.3% vs. 19.2%). Conclusion GPrDs presenting with FTLD is characterized by early‐onset, strong family history, high frequency of the Val allele for codon 129 in PRNP. The clinical features of GPrDs presenting with FTLD is intermediate of the two distinct conditions, while the auxiliary features were closer to that of FTLD. Patients with these characteristics need to be considered for PRNP genotype testing.