FDA shift under acting commissioner lifts rare-disease biotech stocks

40,000 estimated US Huntington’s patients have no approved treatment shown to slow disease

The FDA under acting Commissioner Kyle Diamantas has walked back several high-profile drug decisions, opening an opportunity for investors in rare-disease biotechnology companies that had faced earlier agency skepticism.

In the first year of the current Trump administration, the FDA’s previous leadership had grown skeptical of approving drugs tested in tiny patient groups, sometimes without the usual features of large trials, such as placebo controls. Rare-disease shares plunged as companies in this corner of biotech struggled to navigate a more demanding evidentiary landscape.

That stance is now reversing. The FDA’s new leadership approved Replimune’s melanoma treatment on its third attempt, a case that had become a flashpoint under the previous FDA and drew White House involvement. Replimune’s stock soared in August after the approval but has since given back some of the gains as new questions emerged about whether insurers will pay for treatments that can cost millions of dollars and whether the drug will prove safe and effective enough for patients to take the risk.

Biotech uniQure sits at the preapproval moment of the trade. The company is developing a one-time gene therapy for Huntington’s disease that aims to slow progression of the neurodegenerative disorder. After releasing positive data in the fall of 2025, its stock quadrupled. Then came the reversal: FDA officials said the trial design their predecessors had accepted would no longer suffice for accelerated approval, questioning results drawn from a comparison with a historical database rather than a placebo group and pushing uniQure toward a lengthy randomized trial before refiling. The stock cratered.

In June, the FDA’s new leadership flipped again, agreeing to let uniQure file for approval. The company filed earlier this month, and its stock has more than doubled over the past six months while remaining well below last year’s high. By the end of this month, uniQure is expected to present four-year data from the clinical trial.

The FDA’s approval decision will rest on the three-year results already released, according to Joseph Thome, an analyst at TD Cowen. But the four-year data will still be closely scrutinized by investors and regulators. The earlier results suggested that a high dose of the therapy slowed disease progression by 75% compared with a historical database of patients. If that rate improves or stays relatively stable at four years, it would point to a durable effect, strengthening the case for the gene therapy, which is infused into the brain through a hole in the skull.

Thome said the odds of accelerated approval are “skewing positive,” in part because the FDA is going back to its “old body language.” At a market capitalization of about $3 billion, uniQure still isn’t priced for success, he added. Huntington’s affects an estimated 40,000 people in the U.S., and there are currently no approved treatments shown to slow the disease. A one-time gene therapy, at the prices such treatments command, could make even a relatively small share of that population worth billions of dollars in annual sales.

The Regenxbio case shows that more flexibility at the FDA is no guarantee of success. In June, the FDA reversed its rejection of the company’s gene therapy for a rare inherited disorder, clearing the way for a resubmission and sending the stock higher. Then in August, the shares plunged after the agency placed the therapy on clinical hold when spinal scans turned up abnormalities in some trial participants.

More broadly, willingness to expedite drugs to desperate patients does not mean standards have been lowered, according to Ipsita Smolinski, a healthcare policy consultant. The FDA has grown “more willing to separate approval now from proven clinical benefit later,” she said. The accelerated approval pathway still requires a drug approved on an interim measure of benefit to be studied in a more rigorous confirmatory trial, a step uniQure will still have to take.

The bet on the FDA’s shift is therefore not that uniQure’s therapy works — that question might not be settled for years, if a confirmatory trial ever fully settles it. The bet is that the FDA is once again willing to let patients and investors take that risk before all the evidence is in.