Creutzfeldt-Jakob Disease (CJD)

Definition

Creutzfeldt-Jakob Disease (CJD) is a rare, progressive, and fatal neurodegenerative disorder caused by the accumulation of misfolded prion proteins in the brain. It is the most common human form of transmissible spongiform encephalopathy (TSE).

Symptoms

  • Rapidly progressive dementia.
  • Myoclonus (sudden, involuntary muscle jerks).
  • Visual disturbances or blindness.
  • Ataxia (lack of muscle coordination).
  • Speech impairment and difficulty swallowing.
  • In late stages, profound cognitive impairment and death (usually within one year of symptom onset).

Subtypes

  • Sporadic CJD (sCJD): Most common (85%), occurs randomly with no known cause.
  • Familial CJD (fCJD): Due to mutations in the PRNP gene on chromosome 20.
  • Iatrogenic CJD (iCJD): Accidental transmission during medical procedures (e.g., contaminated surgical instruments, human growth hormone).
  • Variant CJD (vCJD): Linked to the consumption of beef contaminated with bovine spongiform encephalopathy (BSE, or “mad cow disease”).

Mechanisms

  • Prion Hypothesis: The disease is caused by the conformational conversion of the cellular prion protein ($PrP^C$) into the pathological scrapie isoform ($PrP^{Sc}$).
  • Spongiform Change: Characterized by the formation of microscopic vacuoles in the brain tissue, giving it a sponge-like appearance.