Huntington's Disease (HD)
Autosomal-dominant CAG trinucleotide repeat expansion in the HTT gene (chromosome 4p16.3, mean adult onset ~40) — chorea, cognitive decline, and psychiatric features in a defined progressive trajectory — where genetic counseling is the load-bearing precondition, VMAT2 inhibitors (tetrabenazine 2008, deutetrabenazine 2017, valbenazine / Ingrezza FDA August 2023 for HD-associated chorea) anchor symptomatic chorea management, SSRI / SNRI and antipsychotic layers manage psychiatric features, the HTT-lowering trial program (tominersen GENERATION HD1 paused 2021 then restarted in lower-dose / younger-patient cohorts, branaplam discontinued 2022, pridopidine PROOF-HD missed primary endpoint 2023, AMT-130 AAV5-miRNA Phase 1/2 ongoing) drives the disease-modifying conversation, and the editorial honest answer for this trigger is that no peptide in the Juno library has a defensible discovery-card case.
What changes during this transition
Huntington's disease is a defined clinical disease — autosomal-dominant trinucleotide-repeat-expansion neurodegeneration caused by a pathogenic CAG repeat expansion in exon 1 of the HTT gene on chromosome 4p16.3, with the resulting polyglutamine-expanded huntingtin protein driving selective medium spiny neuron loss in the striatum (caudate and putamen) and subsequent cortical involvement. Repeat-length biology is editorially load-bearing: 26 or fewer CAG repeats is normal; 27-35 is intermediate (no clinical HD risk in the individual but expansion-instability risk for offspring); 36-39 is reduced-penetrance HD (variable adult onset); 40 or more is fully-penetrant HD with mean adult onset around age 40 and an inverse relationship between repeat length and age of onset that drives the genetic-anticipation pattern across generations (paternal transmission carries higher expansion-instability risk). The juvenile HD subtype (Westphal variant, onset under age 20, typically inherited from an affected father with very high repeat counts) presents with rigidity, bradykinesia, dystonia, seizures, and rapid cognitive decline. The clinical triad — motor (chorea evolving to dystonia, rigidity, and gait disorder; impaired saccade initiation; dysarthria; dysphagia), cognitive (executive dysfunction predominating early, with psychomotor slowing, progression to subcortical dementia), and psychiatric (depression with disproportionately high suicide risk especially at the time of genetic-test disclosure and at functional decline transitions, anxiety, irritability, apathy, obsessive-compulsive features, and a documented psychosis subset) — is the diagnostic frame. Mean survival from motor symptom onset is roughly 15-20 years. Genetic counseling is the load-bearing precondition. The HDSA (Huntington's Disease Society of America), HSC (Huntington Society of Canada), EHDN (European Huntington's Disease Network), and counterpart organizations across jurisdictions maintain testing protocols that are not optional — predictive (presymptomatic) testing in at-risk individuals follows a multi-visit protocol with pretest counseling, mental-health screening, partner involvement, and explicit acknowledgment of the suicide-risk window around result disclosure; diagnostic testing in symptomatic individuals confirms the clinical impression; prenatal testing and preimplantation genetic diagnosis (PGD) are reproductive options that families navigate with genetic counselors; non-disclosing PGD allows reproductive testing without revealing the prospective parent's own status. Test uptake among at-risk individuals globally runs around 10-20%, reflecting how heavy this decision is. Standard-of-care is symptomatic and supportive across the disease course, with the disease-modifying conversation centered on trial enrollment because no registered disease-modifying therapy exists. The chorea-management ladder is VMAT2 inhibitors: tetrabenazine (Xenazine, FDA-approved 2008, with depression and suicidality black-box warnings and the CYP2D6 metabolism interaction); deutetrabenazine (Austedo, FDA-approved 2017, deuterated for longer half-life and improved tolerability profile); and valbenazine (Ingrezza, FDA-approved August 2023 for chorea associated with Huntington's disease on the basis of the KINECT-HD Phase 3 trial). All three carry depression / suicidality / parkinsonism / akathisia class concerns. Antipsychotics (olanzapine, risperidone, quetiapine, haloperidol, aripiprazole) cover chorea plus psychiatric symptoms. SSRIs (sertraline, citalopram, escitalopram) and SNRIs are first-line for the depression and anxiety burden. Mood stabilizers (valproate, carbamazepine) cover irritability and impulsivity. The disease-modifying trial story is editorially load-bearing. Tominersen (Roche / Genentech / Ionis IONIS-HTTRx, an antisense oligonucleotide intrathecally administered to lower huntingtin mRNA and protein production) entered the GENERATION HD1 Phase 3 trial after positive Phase 1/2 biomarker data, and the trial was paused in March 2021 by the independent data-monitoring committee for futility and possible signal of clinical worsening at the higher-dose arm. Tominersen was subsequently restarted in 2022 with a different program design (GENERATION HD2) targeting lower-dose / younger-patient cohorts. Branaplam (Novartis LMI070, an oral splice modulator originally developed for spinal muscular atrophy and repurposed for HD) had its HD program discontinued in 2022 after a Phase 2b safety signal of peripheral neuropathy. Pridopidine (Prilenia PRIDE-HD and PROOF-HD Phase 3, a sigma-1 receptor agonist) missed the primary endpoint in the PROOF-HD Phase 3 readout in April 2023. AMT-130 (uniQure, AAV5-delivered microRNA-based intrathecal HTT-lowering gene therapy) is the most editorially current ongoing disease-modifying program, with Phase 1/2 dose-finding data reported through 2024-2025 showing CSF neurofilament light-chain (NfL) signal and tolerability findings, and is the actionable gene-therapy trial-enrollment route at the editorial cutoff. The EAN / MDS joint guideline, the HSG (Huntington Study Group) recommendations, and the Enroll-HD observational registry are the cross-jurisdictional anchors. Where Juno's library fits — narrowly and with deliberate non-elevation. No peptide in the library has a discovery-card-defensible HD case. The five drafted substrate entries (Cerebrolysin, Semax, SS-31, NMN, BPC-157) exist for honest /ask answers when users probe specific compounds, not for browse elevation. Cerebrolysin's registered dementia and stroke indications across 50+ jurisdictions do not propagate to a monogenic autosomal-dominant trinucleotide-repeat-expansion disorder. Semax has a Russian Ministry of Health registered indication for cerebrovascular insufficiency that does not engage the HTT-driven polyglutamine toxicity pathway. SS-31 / elamipretide is the most mechanistically defensible peptide-class HD case because striatal mitochondrial dysfunction is well-characterized in HD postmortem tissue and animal models — but there is no published SS-31 HD trial in any jurisdiction. NMN's NAD+-precursor biology does not propagate to a monogenic polyglutamine disease. BPC-157 is community framing only — the Sikiric Zagreb corpus does not engage huntingtin biology, and the WADA S0 status matters for any HD-gene-carrier athlete who is still presymptomatic and competing. The honest editorial frame: genetic counseling, HDSA / EHDN / equivalent multidisciplinary clinic coordination, the VMAT2-inhibitor chorea-management ladder and the SSRI / antipsychotic psychiatric-management layers, AMT-130 trial enrollment, and the Enroll-HD natural-history registry placement drive outcomes; no peptide in the library substitutes.
Important caveat
HD is genetics-and-movement-disorder-neurology-managed standard-of-care disease — genetic counseling is the LOAD-BEARING PRECONDITION for nearly every decision on this axis, and that is not optional. Predictive (presymptomatic) testing in at-risk individuals follows the HDSA / EHDN multi-visit protocol with pretest counseling, mental-health screening with explicit suicide-risk assessment, partner and family involvement, and post-test follow-up at and around result disclosure (the disclosure window carries elevated suicide risk and is not a clinic visit to skip); diagnostic testing in symptomatic individuals confirms the clinical impression with CAG repeat sizing; prenatal testing and preimplantation genetic diagnosis (PGD) are reproductive-decision routes families navigate with genetic counselors. CAG repeat sizing matters: 26 or fewer normal; 27-35 intermediate; 36-39 reduced-penetrance HD; 40 or more fully-penetrant HD with mean adult onset around age 40 and the inverse repeat-length-to-onset-age relationship driving genetic-anticipation patterns. Juvenile HD (Westphal variant, under age 20) presents with rigidity, dystonia, bradykinesia, and seizures. Standard-of-care chorea management is VMAT2 inhibitors: tetrabenazine (Xenazine, FDA 2008, with depression and suicidality black-box warnings and CYP2D6 metabolism interactions); deutetrabenazine (Austedo, FDA 2017); valbenazine (Ingrezza, FDA August 2023 for chorea associated with HD on KINECT-HD Phase 3). All three carry depression / suicidality / parkinsonism / akathisia class concerns. Antipsychotics (olanzapine, risperidone, quetiapine, haloperidol, aripiprazole) cover chorea plus psychiatric symptoms; SSRIs (sertraline, citalopram, escitalopram) and SNRIs are first-line for depression and anxiety; mood stabilizers (valproate, carbamazepine) for irritability and impulsivity. The disease-modifying trial story is editorially load-bearing: tominersen (Roche / Ionis IONIS-HTTRx ASO) GENERATION HD1 Phase 3 paused March 2021 for futility and possible higher-dose worsening signal, restarted in 2022 (GENERATION HD2) with lower-dose / younger-patient / CAP-score-stratified cohorts; branaplam (Novartis LMI070 oral splice modulator) HD program discontinued 2022 after Phase 2b peripheral-neuropathy signal; pridopidine (Prilenia PROOF-HD Phase 3 sigma-1 agonist) missed primary endpoint April 2023; AMT-130 (uniQure AAV5-delivered miRNA intrathecal HTT-lowering gene therapy) Phase 1/2 ongoing through 2024-2025 with CSF NfL biomarker signal is the editorially load-bearing actionable gene-therapy enrollment route. EAN / MDS joint guideline, HSG recommendations, and the Enroll-HD international observational natural-history registry are the cross-jurisdictional anchors. Multidisciplinary clinic coordination runs through HDSA Centers of Excellence and the European Huntington's Disease Network and equivalent international networks. HD Buddies, HDYO (children and young adults in HD families), and patient-and-family-facing community organizations are part of the support and trial-enrollment infrastructure. No Juno library peptide is surfaced as an HD discovery card. Rule 6 non-propagation is editorially load-bearing on this trigger: cerebrolysin's registered dementia and stroke indications across 50+ jurisdictions do NOT propagate to monogenic autosomal-dominant trinucleotide-repeat-expansion neurodegeneration; semax's Russian cerebrovascular-insufficiency indication does NOT propagate to HTT-driven polyglutamine toxicity; SS-31's Barth syndrome FDA approval (March 2025) and dry-AMD ReCLAIM-2 Phase 2b miss (December 2023) do NOT propagate; NMN's NAD+-precursor general-aging case does NOT propagate to a monogenic polyglutamine disease, and the neighboring nicotinamide riboside small HD exploratory work does NOT propagate to NMN; BPC-157's Sikiric Zagreb gastric and tendon corpus does NOT propagate to striatal medium-spiny-neuron biology. WADA athletes who are gene-positive but still presymptomatic and competing: BPC-157 (S0 Non-Approved Substances) is prohibited at all times. Pregnancy and reproductive decision-making in HD families is a specialist conversation that runs through genetic counseling, with PGD and prenatal testing as the existing routes. The depression and suicide risk in HD is disproportionately elevated relative to general-population baseline — especially at the test-result-disclosure window and at functional-decline transitions — and any clinician conversation about adding a peptide on this axis runs alongside the standing psychiatric assessment, not in place of it.
Want this list to grow? The library is editorial — if there’s a peptide you think belongs on this page with documented or mechanistically-clear evidence, send us a note with the citation and we’ll review it under the same evidence-tier discipline as every other entry.