Ultragenyx's Angelman Syndrome Drug Fails Phase 3 Trial, Shares Plunge 40%
- Ultragenyx's Phase 3 ASPIRE trial tested apazunersen (GTX-102), an antisense oligonucleotide, in children and adolescents with Angelman syndrome.
- The therapy failed to separate from sham on the primary endpoint, a Bayley-4 cognitive score change, and also missed the key secondary Multidomain Responder Index.
- No consistent efficacy signal emerged across the individual measures making up that secondary endpoint.
- Safety data lined up with earlier Phase 1/2 findings, with no new red flags reported.
- Shares of Ultragenyx sank more than 40% in after-hours trading on the news.
- The company said it will decide the program's fate and cut costs while leaning on its approved commercial products.
Angelman syndrome is genetically validated (UBE3A) but remains a graveyard for CNS translation — another reminder that hitting the target biology doesn't guarantee a measurable cognitive readout on Bayley-4. No consistent signal across the Multidomain Responder Index components rules out an easy subgroup-rescue story; this reads as a clean miss, narrowing Ultragenyx to kill-or-redesign rather than reslice-the-data. GTX-102/apazunersen was Ultragenyx's flagship CNS asset for years — the >40% drop erases a large chunk of market cap and pressures near-term capital allocation, even with a clean safety profile. The commercial portfolio (Crysvita, Dojolvi) buys runway to absorb this rather than face an existential crisis, but expect cost cuts and tighter pipeline focus. Broader signal: one more data point against intrathecal ASOs cracking cognitive endpoints in neurodevelopmental CNS disease.
Ultragenyx drug to treat Angelman syndrome, a rare disease, fails late-stage trial ↗