Variably Protease‐Sensitive Prionopathy: Two New Cases With Motor Neuron‐Dementia Syndrome

We describe two patients with variably protease‐sensitive prionopathy (VPSPr) who developed progressive upper motor neuron symptoms, insomnia, behavioral and cognitive decline, compatible with primary lateral sclerosis associated with frontotemporal dementia (FTD). Neuropathology revealed a spongiform encephalopathy with frontotemporal and pronounced thalamic involvement, associated with fine synaptic abnormal prion protein conformer (PrP Sc ) deposits, microplaques, and intraneuronal aggregates. Western blot analysis revealed a characteristic VPSPr proteolytic profile, lacking the diglycosylated band. Both patients were methionine homozygous at PRNP codon 129 and carried no pathogenic mutations. These cases illustrate that VPSPr can present with a prominent motor neuron syndrome and FTD features.