What are Pick bodies composed of?

Pick Bodies Composition

Pick bodies are primarily composed of abnormal tau proteins, specifically hyperphosphorylated tau proteins that form straight filaments of 10-20 nm in diameter. 1

Detailed Composition of Pick Bodies

Primary Components

• Tau proteins: The major structural components of Pick bodies are abnormal tau proteins 2
  • Predominantly three microtubule-binding repeat (3R) tau isoforms 3
  • Some cases also contain four microtubule-binding repeat (4R) tau isoforms 3
  • These tau proteins are hyperphosphorylated 4

Biochemical Characteristics

• Pick bodies exhibit a distinctive tau protein pattern:
  • A 55 and 64 kDa tau protein doublet that appears to be specific to Pick's disease 5
  • This pattern differs from Alzheimer's disease (which shows a 55,64, and 69 kDa triplet) 5
  • The tau proteins in Pick bodies are less acidic than Alzheimer's disease tau proteins 5

Ultrastructural Features

• Sparse 10-20 nm straight filaments 1
• These filaments are admixed with other cytoplasmic elements 1
• The filaments share insolubility characteristics similar to paired helical filaments seen in Alzheimer's disease 1
• Unlike Alzheimer's disease, Pick body filaments typically lack phosphorylation at serine 262 4

Cellular Distribution

• Pick bodies demonstrate a somatoaxonal distribution pattern of hyperphosphorylated tau 4
  • This differs from Alzheimer's disease, which shows a somatodendritic distribution 4
• They are frequently found in the dentate fascia of the hippocampus 2

Clinical Significance

Pick bodies are pathognomonic for Pick's disease, a rare form of frontotemporal dementia characterized by:

• Circumscribed cortical atrophy affecting primarily the frontal and temporal poles 2
• Personality deterioration and memory deficits that are often more severe than visuospatial deficits 2
• Neuronal loss and degeneration maximal in the limbic system 2

Diagnostic Considerations

Pick bodies can be identified through:

• Immunostaining with phosphorylation-dependent anti-tau antibodies (AT270, AT8, AT180, PHF-1, AT10) 4
• Bodian's silver stain, which has high affinity for neurofilaments 1
• Electron microscopy to visualize the characteristic straight filaments 1

Understanding the composition of Pick bodies is crucial for distinguishing Pick's disease from other tauopathies and neurodegenerative disorders, particularly when considering treatment approaches and disease progression.