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Sporadic CJD

Form Cause Distinguishable Features
Sporadic CJD (sCJD) Unknown, but widely believed to be due to a spontaneous misfolding of the normal prion protein. Affects mainly people over the age of 60. Common symptoms include ataxia and dementia. Short course (e.g., 4-6 months). Upon tissue examination there is spongiform change and prion protein deposition.
Sporadic Fatal Insomnia (sFI) Unknown, but widely believed to be due to a spontaneous misfolding of the normal prion protein. Has clinical and histopathologic features indistinguishable from those of Fatal Familial Insomnia (FFI) (see here), but does not have the mutation on the prion gene that characterizes FFI.
Variably Protease Sensitive Prionopathy (VPSPr) Unknown, but widely believed to be due to a spontaneous misfolding of the normal prion protein. Average age at onset is 70 and clinical signs differ from those of CJD, with patients presenting with psychiatric symptoms, speech deficits, and cognitive impairment.  Ataxia and Parkinsonism can develop. Illness duration is typically longer than sCJD. Resembles Gerstmann-Sträussler-Scheinker disease (GSS) in terms of the characteristics of the abnormal prion protein (PrPSc). However, unlike in GSS, no mutations in the prion protein gene have been identified.
Sporadic subtypes

Sporadic forms of prion disease are broken down into subtypes, based on the combination of normal variations (not mutations) of codon 129 of the PrPC gene (e.g., MM, MV, or VV) and the biochemical features of PrPSc (type 1 and/or 2).

 
sCJD type Average Age at Onset Average Duration (mo) Clinical Features
MM1 or MV1 64 3.9 Rapidly progressive dementia, early and prominent myoclonus.
VV2 61 6.5 Ataxia at onset, late dementia.
MV2 60 17 Ataxia in additional to progressive dementia; Long duration (>2 years) in some cases.
MM2-thalamic (a.k.a. sFI) 52 15.6 Insomnia and psychomotor hyperactivity in most cases, in addition to ataxia and cognitive impairment.
MM2 - cortical 64 15.7 Prolonged progressive dementia, early and prominent neuropsychological deficits, aphasia and apraxia.
VV1 39.5 15.3 Slowly progressive dementia, personality changes, psychiatric conditions.