The Gene Therapy That Worked for 3 Years, Then Stopped Working
uniQure's Huntington's gene therapy looked like a breakthrough at three years. Then the four-year data arrived, the stock lost $1 billion in value, and the entire promise of gene therapy in brain disease came under scrutiny.
A Billion Dollars, Gone Before Lunch
Imagine training for a marathon for three years. You're hitting every split, looking unbeatable. Then at mile 22, your legs just… stop. That's roughly what happened to uniQure's Huntington's disease gene therapy on September 29, 2026.
The company released four-year follow-up data for AMT-130, its one-time gene therapy for Huntington's disease, and the results told a very different story than the data from a year earlier. Investors panicked. uniQure's stock cratered 37% in a single day. Roughly $1 billion in market value vanished before most people had finished their morning coffee.
The kicker? The FDA is currently reviewing a marketing application for this exact therapy, based on the older, prettier data.
What Looked So Good at Three Years
To understand the meltdown, you need to rewind to the 36-month results. At three years, AMT-130 looked genuinely exciting. High-dose patients showed 80% slowing on a key measure called the cUHDRS (a composite score that tracks how fast Huntington's disease chips away at your motor and cognitive function). The p-value was 0.005, which in science-speak means "this probably isn't a fluke."
For a disease with essentially zero effective treatments, those numbers felt like a lighthouse in the dark. Huntington's is a genetic neurodegenerative disorder that slowly robs people of their ability to move, think, and eventually live. It's caused by a single faulty gene, which makes it a seemingly perfect target for gene therapy: deliver a corrective payload once, and maybe you're done forever.
That "forever" part is where things got complicated.
The 48-Month Reality Check
At four years, the cUHDRS benefit dropped to 44% slowing. Worse, the result was no longer statistically significant (p=0.144). In plain English: the data could no longer confidently rule out that the improvement was due to chance.
That's a brutal swing. Going from 80% slowing to 44% isn't a minor wobble; it's the kind of drop that makes you question whether the therapy's effect is fading with time.
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Now, uniQure pushed back on the doom-and-gloom interpretation. The company pointed to another measure called TFC (Total Functional Capacity, which tracks a patient's ability to handle daily life). On TFC, high-dose patients still showed 61% slowing with a nominal p-value of 0.008. That's not nothing.
uniQure also argued that the updated external control group (the comparison patients who didn't get the therapy) had substantial missing data and possible survivor bias, which could make AMT-130 look worse than it actually is. A post hoc analysis using the original control group showed a more encouraging 54% slowing on cUHDRS. But post hoc analyses are like grading your own homework: useful context, not proof.
The FDA's Awkward Timing
This is where it gets really interesting. The FDA is currently reviewing a BLA (Biologics License Application, basically the formal request for marketing approval) for AMT-130 under the accelerated approval pathway. uniQure submitted it in September 2026.
The application is built on the 36-month data, not the 48-month data.
The regulatory backstory has its own twists. Back in March 2026, the FDA told uniQure that its Phase I/II data versus an external control weren't strong enough for a marketing application. The agency pushed for a full-blown Phase III trial with sham surgery controls. Then, by June, the FDA reversed course and agreed that 36-month data from 15 high-dose patients could support an accelerated approval filing.
Fifteen patients. That's fewer people than a jury.
So now the FDA has to decide: does it approve a therapy based on 36-month data when the 48-month data looks significantly weaker? Accelerated approval lets drugs onto the market based on surrogate or intermediate endpoints, with the requirement that the company runs a confirmatory study afterward. But the optics of approving something whose signal appears to be fading in real time would be, to put it mildly, uncomfortable.
The Bigger Question for Gene Therapy
This isn't just a uniQure story. It's a stress test for the entire promise of gene therapy in brain diseases.
The pitch for AAV-based gene therapy (AAV is the viral delivery vehicle that carries the therapeutic gene into cells) in the brain has always been elegant: neurons don't divide, so once you get your genetic payload inside them, it should stick around for decades. In theory, one treatment could last a lifetime.
But theory and four-year clinical data are telling different stories. Experts acknowledge that while AAV expression can persist in neurons for years, persistent expression doesn't guarantee persistent clinical benefit. And if the effect does fade, you can't easily re-dose patients because their immune systems develop antibodies against the AAV capsid after the first treatment.
It's a bit like using a skeleton key that only works once. If the lock changes over time, you're stuck outside with no way back in.
A Competitive Landscape That Just Got More Interesting
uniQure isn't the only company chasing Huntington's treatments. Wave Life Sciences is advancing WVE-003, which selectively targets only the mutant copy of the huntingtin gene while leaving the healthy copy alone. PTC Therapeutics is developing an oral option that works through a completely different mechanism.
Each approach has tradeoffs. The RNA drugs and oral therapies require chronic dosing, so patients need repeated treatments. Gene therapy offers a one-shot approach, but only if the effect lasts. AMT-130's wobble at four years makes that "if" feel a lot heavier than it did a year ago.
Voyager Therapeutics is also working on an AAV-based gene therapy for Huntington's, though it's much earlier in development. If uniQure's durability concerns deepen, Voyager's program could face guilt-by-association skepticism from investors.
Where This Leaves Us
Analysts, interestingly, haven't abandoned ship. The consensus rating remains "Moderate Buy" with an average price target of $59.55, more than double where the stock landed after the selloff. That gap between analyst optimism and investor panic tells you something: Wall Street's long-term models still see a path, but the market's near-term confidence is shattered.
The next major catalyst is the FDA's decision on the BLA filing. If the agency accepts the application for review and grants priority review, that shortened timeline could give investors something concrete to rally around. If the FDA pushes back or requests additional data reflecting the 48-month results, the stock likely has further to fall.
For Huntington's patients and their families, the stakes are infinitely higher than any stock chart. AMT-130 may still work; a 44% slowing of disease progression, even if the statistical confidence has weakened, would be meaningful in a disease with no approved treatments that alter its course. But the gap between "may work" and "definitely works" is exactly the gap that clinical trials are supposed to close.
At four years, that gap is wider than anyone hoped.
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