| Chromosomal Location | 4p16.
The HTT gene encodes huntingtin, a large (~3,144 amino acids) protein of unknown normal function. It is one of the largest genes in the human genome:
- Protein interaction hub: Huntingtin interacts with over 100 proteins involved in transcription, transport, signaling, and autophagy
- Neuroprotection: Wild-type huntingtin is neuroprotective; loss of function contributes to neurodegeneration
- Vesicle trafficking: Involved in synaptic vesicle transport and neurotransmitter release
- Transcriptional regulation: Interacts with transcription factors including REST, NCoR, and p53
- Autophagy: Regulates selective autophagy and mitophagy
- Cellular scaffolding: Associates with microtubules and actin cytoskeleton
The polyglutamine (polyQ) tract in the N-terminus is polymorphic in the normal population (6-35 repeats).
- Inheritance: Autosomal dominant
- Mechanism: CAG repeat expansion (>35 repeats) in the HTT gene
- 36-39 repeats: reduced penetrance (may or may not develop HD)
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39 repeats: full penetrance
- Pathogenesis:
- Mutant huntingtin (mHTT) forms toxic aggregates
- Loss of normal huntingtin function
- Transcriptional dysregulation
- Impaired mitochondrial function
- Excitotoxicity
- Disrupted autophagy
- Anticipation: Earlier onset in subsequent generations (paternal transmission tends to expand repeats)
- High expression: Brain (throughout), testis, ovary
- Cellular localization: Cytoplasmic, associated with organelles
- Regional specificity: High in striatal medium spiny neurons (most vulnerable)
- Allen Brain Atlas: High expression in striatum, cortex, cerebellum
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The Huntington's Disease Collaborative Research Project. (1993). "A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington's disease chromosomes." Cell. PMID:8454145
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Trottier Y, et al. (1995). "Polyglutamine expansion as a pathological epitope in Huntington's disease and four dominant cerebellar ataxias." Nature. PMID:7545954
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Zuccato C, et al. (2010). "Huntingtin as a gene-regulatory protein acting on chromatin." Brain Res Bull. PMID:20206240
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Cattaneo E, et al. (2001). "Loss of normal huntingtin function: new developments in Huntington's disease research." Trends Neurosci. PMID:11182455
The study of Htt Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
1 The Huntington's Disease Collaborative Research Project. (1993). A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington's disease chromosomes. Cell. [PMID:8454145](https://pubmed.ncbi.nlm.nih.gov/8454145/).
2 Landles C, et al. (2010). Huntingtin and its role in neuronal degeneration. Nat Rev Neurosci. [PMID:20474201](https://pubmed.ncbi.nlm.nih.gov/20474201/).
3 Tabrizi SJ, et al. (2011). Predictability of manifest Huntington's disease within 10 years. Brain. [PMID:21850189](https://pubmed.ncbi.nlm.nih.gov/21850189/).
4 Ross CA, et al. (2014). Huntington disease: natural history, biomarkers and prospective therapeutics. Nat Rev Neurol. [PMID:24468805](https://pubmed.ncbi.nlm.nih.gov/24468805/).
5 DiFiglia M, et al. (1997). Huntingtin is a cytoplasmic protein associated with vesicles in neuronal and axonal terminals. J Neurosci. [PMID:9045728](https://pubmed.ncbi.nlm.nih.gov/9045728/).
- See: Huntingtin Protein - Protein product
- See: Huntington's disease - Disease context
- See: CAG Repeat Disorders - Disease category
- See: Striatal Medium Spiny Neurons - Vulnerable cell type
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