Human prion diseases

Related Subjects: |Dementias |Gerstmann-Straussler-Scheinker Syndrome (GSS) |Fatal Familial Insomnia (FFI) |Creutzfeldt Jakob disease (CJD) |Variant Creutzfeldt Jakob disease (vCJD) |Kuru

🧠 About

• There are five major human prion diseases, each with distinct clinical and genetic features.
• 🌀 A prion is a misfolded protein that induces normal proteins to misfold, causing toxic accumulation.
• Also known as Transmissible Spongiform Encephalopathies (TSEs), these are progressive, fatal neurodegenerative disorders.

✨ Key Features of Prion Diseases

• ⚡ Rapidly progressive neurodegeneration → severe cognitive and motor decline.
• 🧑‍⚕️ Affect both humans and animals (e.g., BSE in cows, scrapie in sheep).
• ⏳ Long incubation periods (years–decades) before symptoms appear.
• 🔬 Characterized by spongiform changes in brain tissue (vacuoles → “sponge-like” appearance).
• ❌ Notably no inflammatory response – unlike other infections or dementias.

🧪 Pathology

• Spongiform Change: Microscopic vacuoles in neurons & neuropil.
• Neuronal Loss: Especially cortical layers III–V, basal ganglia, thalamus, cerebellum.
• Prion Protein Accumulation (PrP^Sc): Protease-resistant deposits disrupt function.
• No Inflammation: Distinctive from other neurodegenerative diseases.

📌 Types of Human Prion Diseases

• 🧩 Creutzfeldt–Jakob Disease (CJD)
  • Most common. Presents with rapid dementia, myoclonus, ataxia.
  • Majority are sporadic (sCJD); others familial or iatrogenic.
  • CSF marker: 14-3-3 protein (supportive, not specific).
  • Median survival: 6–12 months.
• 🥩 Variant CJD (vCJD)
  • Linked to BSE exposure (“mad cow disease”), especially in UK epidemic.
  • Typically affects younger patients (<40 years).
  • Early psychiatric symptoms → later cognitive decline & motor signs.
  • Neuropathology: “florid plaques” + thalamic involvement.
• 🌍 Kuru
  • Endemic to Papua New Guinea, due to ritual cannibalism.
  • Mainly cerebellar involvement → tremors, ataxia, emotional lability.
  • No new cases since practice abolished.
• 🧬 Gerstmann–Sträussler–Scheinker (GSS)
  • Inherited PRNP mutation.
  • Early adulthood onset: ataxia, dementia, parkinsonism, deafness.
  • Progression: slower (years), amyloid plaques in brain.
• 🌙 Fatal Familial Insomnia (FFI)
  • PRNP mutation, classic in Italian families.
  • Unique: progressive insomnia, autonomic failure, hallucinations, dementia.
  • Pathology: Selective thalamic degeneration.

🧾 Investigations

• CSF: 14-3-3 protein (supportive); RT-QuIC test is highly specific.
• Genetic Testing: PRNP mutations confirm familial forms; codon 129 polymorphism modulates risk.
• MRI: CJD → cortical ribboning/basal ganglia hyperintensity; vCJD → pulvinar sign; FFI → thalamic atrophy.
• EEG: sCJD → periodic sharp wave complexes.
• Histology: Spongiform change, prion protein deposits; definitive at biopsy/autopsy.

⚕️ Management

• ❌ No cure – care is supportive.
• 💊 Symptom relief: anticonvulsants (for myoclonus), antipsychotics, sedatives.
• 👩‍👩‍👧‍👦 Multidisciplinary: nursing, psychological, and palliative care support.
• 🧼 Infection control: special sterilisation protocols (prions are resistant to standard autoclaving).

📉 Prognosis

• Uniformly fatal – sCJD median survival ~6–12 months.
• Inherited forms (GSS, FFI) → slower course (years).
• Research: experimental therapies target prion replication/clearance, but no proven treatment yet.

📚 References

• National Prion Disease Pathology Surveillance Center
• Prion Diseases and Mechanisms of Neurodegeneration

Cases - Human Prion Diseases

• Case 1 - Sporadic Creutzfeldt–Jakob Disease (sCJD): A 64-year-old man develops rapidly progressive memory loss, ataxia, and myoclonus over 6 weeks. EEG shows periodic sharp wave complexes; MRI shows cortical ribboning and basal ganglia hyperintensity. Diagnosis: Sporadic CJD. Management: Supportive; palliative MDT input; prognosis poor (median survival ~6 months).
• Case 2 - Variant Creutzfeldt–Jakob Disease (vCJD): A 28-year-old woman presents with depression, anxiety, and painful dysaesthesias. Over months she develops cognitive decline and ataxia. MRI brain: pulvinar (“hockey-stick”) sign. Diagnosis: Variant CJD (linked to bovine spongiform encephalopathy). Management: Supportive, palliative; infection control measures.
• Case 3 - Familial CJD (Inherited): A 52-year-old man with family history of early dementia presents with rapidly progressive cognitive decline, gait disturbance, and myoclonus. Genetic testing shows PRNP mutation. Diagnosis: Familial CJD. Management: Genetic counselling; supportive neurological and palliative care.
• Case 4 - Gerstmann–Sträussler–Scheinker (GSS) Syndrome: A 45-year-old woman develops slowly progressive cerebellar ataxia and dysarthria, followed by dementia over several years. Family history of similar illness. Diagnosis: GSS (rare inherited prion disease). Management: Supportive; physiotherapy for ataxia; genetic counselling.
• Case 5 - Fatal Familial Insomnia (FFI): A 50-year-old man presents with severe insomnia, autonomic hyperactivity (sweating, tachycardia), and progressive confusion. Over months, he develops dementia and wasting. PRNP mutation confirmed. Diagnosis: Fatal familial insomnia. Management: Supportive only; sleep aids often ineffective; prognosis poor.

Teaching Commentary 🧠

Prion diseases are rare, fatal, neurodegenerative disorders caused by misfolded prion proteins (PrP^Sc) that induce abnormal folding of normal prion proteins. - Sporadic CJD: most common, rapid progression, myoclonus, cortical ribboning on MRI. - Variant CJD: younger onset, psychiatric prodrome, pulvinar sign, linked to BSE. - Familial forms: due to PRNP mutations (CJD, GSS, FFI). - Key features: rapid dementia, ataxia, myoclonus, cortical/thalamo involvement. Diagnosis: MRI, EEG, CSF RT-QuIC assay, genetic testing. No cure - management is supportive and palliative, with strict infection control due to prion resistance to sterilisation.