A novel subtype of sporadic Creutzfeldt-Jakob disease with PRNP codon 129MM genotype and PrP plaques

The presence of amyloid kuru plaques is a pathological hallmark of sporadic Creutzfeldt-Jakob disease (sCJD) of the MV2K subtype. Recently, PrP plaques (p) have been described in the white matter of a small group of CJD (p-CJD) cases with the 129MM genotype and carrying resPrP^D type 1 (T1). Despite the different histopathological phenotype, the gel mobility and molecular features of p-CJD resPrP^D T1 mimic those of sCJDMM1, the most common human prion disease. Here, we describe the clinical features, histopathology, and molecular properties of two distinct PrP plaque phenotypes affecting the gray matter (p^GM) or the white matter (p^WM) of sCJD cases with the PrP 129MM genotype (sCJDMM). Prevalence of p^GM- and p^WM-CJD proved comparable and was estimated to be ~ 0.6% among sporadic prion diseases and ~ 1.1% among the sCJDMM group. Mean age at onset (61 and 68 years) and disease duration (~ 7 months) of p^WM- and p^GM-CJD did not differ significantly. PrP plaques were mostly confined to the cerebellar cortex in p^GM-CJD, but were ubiquitous in p^WM-CJD. Typing of resPrP^D T1 showed an unglycosylated fragment of ~ 20 kDa (T1²⁰) in p^GM-CJD and sCJDMM1 patients, while a doublet of ~ 21-20 kDa (T1^21-20) was a molecular signature of p^WM-CJD in subcortical regions. In addition, conformational characteristics of p^WM-CJD resPrP^D T1 differed from those of p^GM-CJD and sCJDMM1. Inoculation of p^WM-CJD and sCJDMM1 brain extracts to transgenic mice expressing human PrP reproduced the histotype with PrP plaques only in mice challenged with p^WM-CJD. Furthermore, T1²⁰ of p^WM-CJD, but not T1²¹, was propagated in mice. These data suggest that T1²¹ and T1²⁰ of p^WM-CJD, and T1²⁰ of sCJDMM1 are distinct prion strains. Further studies are required to shed light on the etiology of p-CJD cases, particularly those of T1²⁰ of the novel p^GM-CJD subtype.