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 (PrPSc) 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.