Etiology and Pathophysiology of Creutzfeldt-Jakob Disease

Introduction to Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob disease is caused by the accumulation of misfolded prion proteins (PrPSc) in the brain, which arise through three distinct mechanisms: spontaneous misfolding (sporadic), inherited genetic mutations (familial), or external transmission (acquired) 1

Sporadic CJD occurs through spontaneous, posttranslational conversion of normal cellular prion protein (PrPc) into the pathological misfolded form (PrPSc) without any identifiable genetic or environmental trigger, representing approximately 85% of all CJD cases with an incidence of 1.5 to 2.0 per million person-years 1
The disease phenotype varies based on methionine/valine polymorphism at codon 129 of the prion gene (PRNP) and the molecular mass of PrPSc (glycotype 1 and 2) 1

Familial CJD results from autosomal dominant gain-of-function mutations in the prion protein gene (PRNP), with the E200K mutation being one of the most common pathogenic variants, and approximately 10-15% of CJD cases are genetic, arising from protein-altering variants in PRNP that follow autosomal dominant inheritance 2

Acquired CJD occurs through external transmission of prions via contaminated medical procedures, dietary exposure to infected tissue, or ritual practices involving brain tissue 3
Iatrogenic transmission routes include contaminated neurosurgical instruments, as standard sterilization does not reliably eliminate prion infectivity and approximately 10 successive decontamination cycles are required to reduce infectivity to negligible levels 3

Variant CJD is caused by transmission of the bovine spongiform encephalopathy (BSE) prion agent from cattle to humans through dietary contamination with BSE-infected beef products, affecting younger individuals (children and young adults) 3
The tissue distribution differs critically: vCJD prion protein extends to lymph nodes, appendix, and tonsils, making it potentially transmissible through medical and surgical interventions involving lymphoid tissue, whereas sporadic CJD prion protein is confined to brain, spinal cord, and posterior eye 3

Once formed, misfolded PrPSc acts as a template for conformational conversion of additional normal PrPc molecules, creating a self-propagating cascade that leads to neuronal death and characteristic spongiform changes in brain tissue 2
The accumulation of PrPSc causes progressive neurodegeneration with pathognomonic spongiform change, and in some cases, plaque formation and localized regional pathology 1

The American Academy of Neurology and other guideline societies recommend that diagnosis is often delayed and phenotypic variability can obscure family history, making PRNP gene sequencing essential for all suspected CJD cases regardless of apparent family history 2