Variably protease-sensitive prionopathy with methionine homozygosity at codon 129 in the prion protein gene.

Variably protease-sensitive prionopathy (VPSPr) is a recently characterised rare subtype of sporadic prion disease, mainly affecting individuals with valine homozygosity at codon 129 in the prion protein gene, with only seven methionine homozygote cases reported to date. This case presents clinical, neuropathological and biochemical features of the eighth VPSPr case worldwide with methionine homozygosity at codon 129 and compares the features with the formerly presented cases.The patient, a woman in her 70s, presented with cognitive decline, impaired balance and frequent falls. Medical history and clinical presentation were suggestive of a rapidly progressive dementia disorder. MRI showed bilateral thalamic hyperintensity. Cerebrospinal fluid real-time quaking-induced conversion was negative, and the electroencephalogram was unremarkable. The diagnosis was established through post-mortem pathological examinations. VPSPr should be suspected in rapidly progressive dementia lacking typical features or paraclinical results of protein misfolding diseases.