# HTT EXON1 Research Report **Protein:** HTT EXON1 **Variant:** Q23_exon1 **UniProt ID:** P42858 **Disease Association:** Huntington's disease **Report Generated:** 2026-07-28 13:10 UTC **AlphaFold Confidence (pLDDT):** 79.6% **Structure Folded:** 2026-06-22 --- ## Structure Summary HTT exon 1 encodes the first segment of huntingtin protein, where expansions of CAG repeats (encoding polyglutamine tracts) beyond 36 repeats cause Huntington's disease, a fatal neurodegenerative disorder. This structural analysis examined the Q23_exon1 variant, which contains 23 glutamine repeats in the normal range, achieving a good average confidence score of 79.6 that indicates reliable prediction of most structural features. Understanding the normal structure provides essential context for how pathological expansions lead to protein misfolding and the formation of toxic aggregates that particularly damage striatal neurons in the brain. --- The huntingtin (HTT) protein plays critical roles in neuronal health and function throughout the adult brain, with its loss contributing to decreased neuronal excitability and degeneration [5]. Huntington's disease arises when CAG trinucleotide repeats in exon 1 of the HTT gene expand beyond 36 repeats, encoding abnormally long polyglutamine (polyQ) tracts that cause the protein to misfold and form toxic aggregates [1][2]. This structural prediction examined the Q23_exon1 variant containing 23 glutamine repeats, which falls within the normal range and does not cause disease, providing important baseline information about the native protein structure. The AlphaFold2 prediction achieved an average confidence score (pLDDT) of 79.6, indicating generally reliable structural predictions for most regions of this exon 1 segment. This confidence level suggests the model can capture key structural features of the normal huntingtin exon 1, though some regions may show lower confidence typical of intrinsically disordered segments. The polyglutamine tract itself is expected to adopt flexible conformations in the normal-length variant, contrasting with pathological expansions where extended polyQ tracts drive misfolding and aggregation [1][2]. Recent research has revealed that the length of CAG repeats in HTT exon 1 profoundly affects cellular function, with extensive transcriptomic changes observed in both cellular and animal models as repeat length increases [1]. In pathological contexts with expanded repeats, the mutant HTT protein forms inclusion bodies whose role remains debated—recent evidence suggests these aggregates may actually be protective rather than toxic, with ATF3-dependent inclusion body formation conferring cellular protection in human iPSC-derived neurons [2]. The mutant HTT transcript also contributes to disease through RNA-mediated toxicity by aberrantly recruiting RNA-binding proteins like MID1 [3]. Clinical implications extend beyond the well-established CAG repeat length, as loss of interrupting codons in the CAG and CCG repeats (CAG-CCG LOI variants) can lead to underestimation of repeat length by current diagnostic assays, affecting disease prediction and clinical trial interpretation [6]. The normal Q23 variant analyzed here provides structural reference data for understanding how pathological expansions disrupt protein structure and function. Striatal spiny projection neurons show particular vulnerability to mutant huntingtin toxicity, experiencing mitochondrial dysfunction, disrupted intracellular transport, and eventual degeneration [4][5], with DNA methylation changes in the striatum associated with disease progression [7]. ## Works Cited [1] Szulc et al. (2026). Extensive transcriptomic changes in cellular and animal models of Huntington's disease depending on the length of CAG repeats in the exon 1 of the HTT gene. Biochemical and biophysical research communications. [PubMed](https://pubmed.ncbi.nlm.nih.gov/41926793/) [2] Oweis et al. (2026). ATF3-dependent formation of inclusion bodies in polyQ-expressing human iPSC-derived neurons confers cellular protection. Cell death and differentiation. [PubMed](https://pubmed.ncbi.nlm.nih.gov/41922802/) [3] Geraci et al. (2026). Aberrant expression of the MID1 protein in neurons of Huntington's disease brain. Frontiers in genetics. [PubMed](https://pubmed.ncbi.nlm.nih.gov/41884622/) [4] Pasko et al. (2026). Mitochondria "Shackled" by Mutant Huntingtin: Analysis of Morphological Alterations and Disruptions of Intracellular Transport. Biochemistry. Biokhimiia. [PubMed](https://pubmed.ncbi.nlm.nih.gov/41843843/) [5] Barron et al. (2026). Striatal Neuron Excitability Is Regulated by Huntingtin in the Adult Brain. eNeuro. [PubMed](https://pubmed.ncbi.nlm.nih.gov/42209021/) [6] Findlay et al. (2026). Clinical implications of loss of interruption variants for diagnosis, genetic counselling, and clinical trials in Huntington's disease. Journal of Huntington's disease. [PubMed](https://pubmed.ncbi.nlm.nih.gov/42202221/) [7] Wheildon et al. (2026). DNA methylation profiling in Huntington's disease reveals disease associated changes in the striatum. Clinical epigenetics. [PubMed](https://pubmed.ncbi.nlm.nih.gov/42185880/) ## Similar Research **Induced pluripotent stem cells from a transgenic minipig model of Huntington's disease reveal early metabolic changes.** Rysankova et al. (2026) *Relevant to Huntington's disease research* [Read on PubMed](https://pubmed.ncbi.nlm.nih.gov/42109206/) **Unraveling the genetic architecture of non-Huntington chorea: a biobank-scale study of rare variants and repeat expansions.** Akcimen et al. (2026) *Relevant to Huntington's disease research* [Read on PubMed](https://pubmed.ncbi.nlm.nih.gov/41957010/) **Huntington's disease LIG1 modifier variant increases ligase fidelity and suppresses somatic CAG repeat expansion.** Lee et al. (2026) *Relevant to Huntington's disease research* [Read on PubMed](https://pubmed.ncbi.nlm.nih.gov/41770933/) **Contribution of neuroepigenetics to HD - developmental and aging-related signatures.** Scuto et al. (2026) *Relevant to Huntington's disease research* [Read on PubMed](https://pubmed.ncbi.nlm.nih.gov/41755664/) **The HTT1a protein initiates HTT aggregation in a knock-in mouse model of Huntington's disease.** Papadopoulou et al. (2026) *Relevant to Huntington's disease research* [Read on PubMed](https://pubmed.ncbi.nlm.nih.gov/41622913/) --- ## Agent Findings ### Literature (1) - **2026-06-23:** These papers are highly relevant to HTT exon 1 Q23 variant as they specifically investigate the molecular mechanisms of exon 1-encoded domains (N17 region, polyglutamine tract) and their roles in HD pathogenesis. The studies provide critical insights into therapeutic targeting strategies focused on HTT exon 1, including the identification of specific amino acid residues (L7) essential for toxicity and novel approaches to prevent exon 1 aggregation through engineered chaperones. ### Synthesis (1) - **2026-06-23:** Synthesis of 1 findings (peptides): The HTT EXON1 Q23 variant associated with Huntington's disease shows substantial therapeutic interes... --- *Generated by [Clarity Protocol](https://clarityprotocol.io)* **Data Sources:** - Structure predictions: AlphaFold via ColabFold - Clinical variant data: ClinVar, gnomAD - Disease associations: Open Targets Platform - Research findings: AI agents (PubMed, clinical databases)