HTT Gene and Huntington Disease: Mutations and Clinical Trials
The HTT gene sits on chromosome 4p16.3, and its full name is huntingtin. Orphanet links HTT to 3 rare conditions and lists variants in the gene as a cause of all of them. Trial Friend's Huntington Disease page lists HTT among the genes behind the condition. As of September 29, 2026, 3 recruiting or soon-opening trials on ClinicalTrials.gov name HTT as a gene.
Other symbols for HTT in gene databases: IT15.
What the HTT gene does
HTT makes huntingtin, a protein whose exact job is still unknown but which appears important for nerve cells in the brain and for development before birth. Part of the gene is a CAG repeat that normally appears 10 to 35 times.
Summarized from the HTT page on MedlinePlus Genetics, U.S. National Library of Medicine, checked September 29, 2026.
HTT and Huntington Disease
These condition pages list HTT among the genes behind the condition, checked against genetics references when each page was written.
One disease-causing variant can be enough to cause the condition.
Caused by a CAG repeat expansion in HTT; 40 or more repeats is fully penetrant, 36 to 39 is reduced penetrance.
HTT mutation clinical trials
These recruiting or soon-opening trials mention HTT as a gene in their title, summary, eligibility rules or keywords. Some want people with a variant in it, and others study it more broadly, which is why each trial's own words are shown. In cancer trials the gene change is usually one found in the tumor rather than one a person inherited.
3 trials, checked September 29, 2026. The list refreshes from ClinicalTrials.gov every few hours.
All conditions linked to HTT gene mutations
Orphanet records how each gene relates to each condition. Orphanet links HTT to 3 rare conditions and lists variants in the gene as a cause of all of them.
- Causes it. Disease-causing variants in this gene are a direct cause of the condition.
HTT genetic test results and what a variant can mean
Labs sort each variant they find into 5 groups, from pathogenic and likely pathogenic through uncertain significance to likely benign and benign. Only the first 2 are usually treated as the cause of a condition. A variant of uncertain significance, or VUS, is one without enough evidence either way yet, and labs can reclassify it as research builds.
A genetic counselor or your doctor can explain what a specific result means for you and your family. Our genetic testing guide covers the terms, and MedlinePlus Genetics from the National Library of Medicine has a plain-language page on HTT.
HTT gene questions
What does the HTT gene do?
HTT makes huntingtin, a protein whose exact job is still unknown but which appears important for nerve cells in the brain and for development before birth. Part of the gene is a CAG repeat that normally appears 10 to 35 times. This summary follows MedlinePlus Genetics from the U.S. National Library of Medicine.
Are there clinical trials for people with HTT gene variants?
As of September 29, 2026, 3 recruiting or soon-opening trials on ClinicalTrials.gov name HTT as a gene. Each one is listed on this page with the words from the trial that mention the gene. ClinicalTrials.gov also lists 47 open trials for Huntington Disease, and Match Me on Trial Friend can check those against age, sex, location and treatment history.
What conditions are linked to the HTT gene?
Orphanet links HTT to 3 rare conditions and lists variants in the gene as a cause of all of them. They include Huntington disease, Juvenile Huntington disease and Non-specific syndromic intellectual disability. Orphanet is the European rare disease database run by INSERM in Paris.
How is Huntington Disease inherited?
The inheritance pattern is autosomal dominant. One disease-causing variant can be enough to cause the condition. Caused by a CAG repeat expansion in HTT; 40 or more repeats is fully penetrant, 36 to 39 is reduced penetrance.
What does an HTT variant of uncertain significance mean?
A variant of uncertain significance, or VUS, is a change in the gene that labs don't yet have enough evidence to call disease-causing or harmless. It is not used on its own to diagnose a condition, and labs can reclassify it as research builds. A genetic counselor can explain what a specific result means for you and your family.
Sources
- Gene and condition links from Orphadata (Orphanet, INSERM US14), used under CC BY 4.0, read September 29, 2026.
- Trials from ClinicalTrials.gov, read September 29, 2026.
- HTT gene, MedlinePlus Genetics, U.S. National Library of Medicine.
- Inheritance and gene notes from the Trial Friend condition pages above, each checked against genetics references.
Other gene pages
The gene search covers every gene Orphanet links to a rare disease.