Why Is Ultragenyx (RARE) Stock Down Today?
The Aspire trial of GTX-102 missed both its endpoints — and the measured crater took 43.65% out in fifteen minutes.
- Phase 3 Aspire study of GTX-102 in Angelman syndrome missed its primary and key secondary endpoints.
- Measured from the 20:01 UTC print: -26.01% in one minute, -43.65% by minute fifteen, from $26.53.
- A two-endpoint pivotal miss removes the program's approval value from the stock in real time.
Reaction by asset (real prices)
| Asset | 2m before | At release | +1m | +15m | +1m % | +15m % | Vol vs normal |
|---|---|---|---|---|---|---|---|
| RARE | 26.53 | 26.53 | 19.63 | 14.95 | -26.01% | -43.65% | — |
Ultragenyx's lead Angelman-syndrome program failed its pivotal trial, and the stock cratered. The company reported that its Phase 3 Aspire study of GTX-102 missed both the primary cognitive endpoint and the key secondary measure. Measured from the instant the result crossed our tape at 20:01 UTC on Wednesday 2 September 2026, the stock fell -26.01% in the first minute and stood -43.65% fifteen minutes later, from $26.53 — one of the sharpest single-name reactions we have measured this year.
Key points
- The Phase 3 Aspire study of GTX-102 in Angelman syndrome missed its primary Bayley-4 cognitive endpoint and its key secondary Multidomain Responder Index endpoint.
- Measured reaction: -26.01% in the first minute, -43.65% by minute fifteen, from $26.53.
- The CEO framed the outcome as a loss for the patient community after a program that had shown encouraging Phase 1/2 results.
Why a trial miss repriced almost half the company in minutes
A single-asset pivotal readout is the cleanest binary event in equities: before the print, the price carries a probability-weighted value for the program's approval; the moment the data lands, that probability resolves to near zero and the value attached to it leaves the stock. GTX-102 had generated encouraging Phase 1/2 data, so the market was carrying real approval odds into the readout — which is exactly why missing both the cognitive primary and the responder-index secondary took -43.65% out in fifteen minutes. There is no partial credit in a two-endpoint miss: without the primary, the cognitive-benefit claim has no statistical footing in this study.
What is left after the readout
Ultragenyx is a multi-asset rare-disease company, not a single-program biotech, so the crater prices the loss of one pipeline value rather than the end of the business. The CEO's statement — disappointment for a global patient community that invested in early research — is the language of a company absorbing a setback and continuing, not closing. For a reader tracking the name, the measured -43.65% sets the reference: the market has now removed the Angelman program's contribution, and the next catalysts are the rest of the portfolio.
Why is Ultragenyx (RARE) stock down today?
Its Phase 3 Aspire trial of GTX-102 in Angelman syndrome failed, missing both the primary cognitive endpoint and the key secondary measure. Measured from the instant the failure crossed at 20:01 UTC, the stock fell -26.01% in the first minute and -43.65% within fifteen, from $26.53 — a binary trial readout repricing the asset in real time.
What endpoints did the Aspire trial miss?
The study did not achieve its primary endpoint — change from baseline in the Bayley-4 cognitive raw score — nor its key secondary endpoint, the net response on the Multidomain Responder Index. Missing both leaves no statistical basis for the drug's cognitive benefit in this trial.
What is GTX-102 and Angelman syndrome?
GTX-102 (apazunersen) is an antisense oligonucleotide Ultragenyx was developing for Angelman syndrome, a rare genetic disorder causing severe intellectual disability and developmental delay. The drug had shown encouraging Phase 1/2 results, which is why the confirmatory Phase 3 miss repriced the stock so sharply.
How far did the reaction extend?
Our tape measured -43.65% in the first fifteen minutes; coverage put the after-hours decline above 40%. A failed pivotal readout removes the value the market had assigned to the program's probability of approval, which for a single-asset catalyst is most of the move.
How these numbers were measured
Reaction figures are MoveSurge's own measurement: the price captured at the instant the headline crossed our tape, then one and fifteen minutes later. Trial and financial details are attributed to the company announcement and coverage. The pipeline is described on our editorial standards page.
Sources
-
Ultragenyx Announces Phase 3 Aspire results in Angelman Syndrome
— GlobeNewswire
The Phase 3 Aspire study of GTX-102 did not achieve the primary Bayley-4 cognitive endpoint nor the key secondary Multidomain Responder Index endpoint.
-
Ultragenyx stock plunges 40% on failed Angelman trial
— Investing.com
Ultragenyx shares fell over 40% in after-hours trading following the failed Phase 3 readout.
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