Huntington's disease gene therapy: FDA reversal delays AMT-130

At the end of September 2025, a gene therapy company released results from a clinical trial showing that a breakthrough procedure reduced the progression of Huntington’s symptoms by 75 percent over three years. Researchers collected data from 12 participants who received the therapy and compared the data with two types of control groups.

The company’s drug, AMT-130, shows unprecedented outcomes, so why is the FDA slowing this treatment from reaching over 40,000 Americans living with this fatal condition?

Huntington’s disease is a genetic condition most often diagnosed midlife. Symptoms may begin as anxiety, forgetfulness, and other neurological changes, progressing to extreme personality changes and complete physical disability requiring around-the-clock care. Trial data indicate that AMT-130 slows progression enough that a decline seen in untreated patients after one year would take roughly four years in those who received the one-time infusion.

How the therapy works

AMT-130 uses an AAV (adeno-associated virus) to carry therapeutic genetic instructions into brain cells. This virus does not cause disease in humans, does not replicate, and is a preferred delivery tool in clinical gene therapy. Inside the virus is a small, engineered piece of genetic material called microRNA (miRNA). This miRNA is designed to recognize and silence the messenger RNA (mRNA) of the huntingtin gene (HTT), thereby reducing huntingtin protein production.

This procedure is a one-time, irreversible surgical brain infusion performed over several hours with MRI guidance. Study participants who received AMT-130 were first compared with a placebo group and later with individuals in the Enroll-HD database, the world’s largest observational study of Huntington’s disease.

The role of external control groups

Using the Enroll-HD as a control group is called an external control group and is often used when a randomized placebo-controlled trial is not feasible due to ethical considerations or other barriers, such as with extremely rare diseases, where finding enough participants is difficult.

In the case of the company’s AMT-130, the trial was randomized, with the placebo group receiving a sham procedure. After 12 months, the treatment was offered to all qualifying trial participants. The crossover of the placebo group to the treatment group was built into the study’s design and is considered more ethical when the treatment is potentially beneficial and the disease is progressive, like with Huntington’s.

Researchers continued to follow study participants who received AMT-130 and shifted to an external control group using data on over 20,000 Huntington’s disease families in the Enroll-HD database. The FDA agreed with this shift and supported moving to the next phase, allowing more patients access to this promising treatment.

Regulatory reversal

However, on November 3, 2025, the company announced that it is no longer aligned with the FDA on the regulatory pathway for AMT-130. Until recently, both parties agreed that the company could use data from its Phase I/II trials, compared with participants in the Enroll-HD database, to support a Biologics License Application (BLA) planned for early 2026.

A BLA is the formal request submitted to the FDA seeking approval to market a biologic product. Like a New Drug Application (NDA) for traditional pharmaceuticals, a BLA demonstrates that a product is safe, pure, and potent. BLAs are used for complex therapies such as vaccines and gene therapies and include data from preclinical research, clinical trials, and manufacturing practices to ensure the product meets the FDA’s standards before reaching patients.

The FDA unexpectedly reversed its support and now believes that external control data are not strong enough to serve as evidence for the BLA approval. This is a significant change. As recently as June 2025, the FDA supported this approach and even granted the treatment Breakthrough Therapy and RMAT (Regenerative Medicine Advanced Therapy) designations, in part based on these plans.

What this means for AMT-130

The data has not changed. AMT-130 remains safe, well-tolerated, and capable of slowing HD progression.
This is a regulatory setback, not a scientific setback.
The timeline to approval is now uncertain, particularly amid broader instability in the U.S. government.

Next steps

On January 9, 2026, the company announced it had scheduled a formal Type A meeting with the FDA to discuss the Biologics License Application (BLA) for AMT-130. This meeting is specifically to talk about a potential accelerated approval pathway for the therapy.
The company is engaging regulatory agencies in Europe and the UK, where progress there could benefit global efforts.

Bottom line

Despite the FDA’s sudden reversal, this is a detour, not an end for AMT-130. The therapy’s safety and efficacy signals remain strong; the challenge lies in satisfying shifting FDA regulatory expectations. While deeply disappointing, the company plans to continue engaging with the FDA while also advancing the therapy outside the United States.

Meghan Johnston is a laboratory scientist.