The Foundational Concept: Genes require specific machinery for reading. Mutant huntingtin steals this machinery, silencing critical survival signals particularly brain-derived neurotrophic factor and starving striatal neurons of support.

The Mechanism:

Mutant Huntingtin: The HTT gene CAG repeat expansion produces huntingtin protein with elongated polyglutamine tract. This confers toxic gain-of-function aberrant protein interactions.

CBP Sequestration: CREB-binding protein (CBP) is a histone acetyltransferase essential for transcription. Mutant huntingtin binds CBP via polyglutamine-polyglutamine interaction, aggregating it into inclusions.

Histone Deacetylation: With CBP trapped, histones remain deacetylated chromatin remains condensed, transcriptionally silent. Genes requiring acetylation for access cannot be expressed.

BDNF Silencing: BDNF (brain-derived neurotrophic factor) expression depends on CREB-CBP transcriptional complexes. Cortical neurons produce BDNF for striatal targets. Without CBP, cortical BDNF transcription drops 60-80%.

Striatal Starvation: Striatal neurons receive BDNF via anterograde transport from cortex. Without this trophic support, they undergo slow degeneration explaining selective vulnerability in Huntington's.

Cell-Specific Vulnerability: Medium spiny neurons of striatum depend most on cortical BDNF. They express TrkB receptors and require constant trophic support unlike interneurons using other survival signals.

The Amplification:

Reduced BDNF further lowers huntingtin clearance

Transcriptional dysregulation affects dozens of genes

Mutant huntingtin also disrupts Sp1, TAFII130, p53 pathways

The Timing:

Transcriptional changes precede pathology by years

CBP sequestration increases with aggregate load

Age-related decline in repair mechanisms compounds deficit

Therapeutic Implications:

HDAC inhibitors (suberoylanilide hydroxamic acid, sodium butyrate) compensating for CBP loss

BDNF mimetics or viral delivery bypassing transcription failure

CBP overexpression or stabilization against sequestration

Histone acetyltransferase activators restoring chromatin access

This reframes Huntington's as transcriptional drought essential survival messages never written.