Summary of Situation
Bitopertin is an investigational therapy developed by Disc Medicine for people living with erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP), two ultra-rare diseases in which visible light exposure, including sunlight, can trigger severe phototoxic pain. For people living with EPP and XLP, everyday activities such as walking outside, going to school, working, traveling, or attending family events can come with risk, planning, and fear.
Submission to the US Food and Drug Administration
Bitopertin has shown promising results in two Phase 2 clinical trials, AURORA and BEACON, where it demonstrated clear impact on lowering metal-free protoporphyrin IX (PPIX), a key biomarker in protoporphyria. It is now being studied in the Phase 3 APOLLO trial, which is expected to complete enrollment in March 2026, with top-line results anticipated in the fourth quarter of 2026.
Encouraged by the data generated to date, Disc Medicine submitted a New Drug Application (NDA) to the US Food and Drug Administration(FDA)for bitopertin on September 29, 2025, through the FDA’s Accelerated Approval pathway. The application also received an FDA Commissioner’s National Priority Voucher, reflecting the seriousness of these diseases and the potential importance of this treatment.
FDA Complete Response Letter defers decision
On February 13, 2026, the FDA issued a Complete Response Letter (CRL) for bitopertin. While the agency acknowledged bitopertin’s effect on lowering PPIX, it stated that it wanted more evidence linking those biomarker reductions to meaningful clinical benefit, including improvement in sunlight tolerance. Disc Medicine has said the issues raised are addressable and are not related to chemistry, manufacturing, or controls - and that bitopertin has a strong safety profile.
This decision placed the EPP/XLP community at a critical moment. Unless a faster path is identified, patients may now be forced to wait until at least 2027 for a potential approval decision. For a community living with painful and life-limiting disease, that delay is deeply significant. It means more missed time, more isolation, and more seasons lost waiting for a treatment that could help people experience something most take for granted: time in the sun without pain.
Our community cannot afford to lose momentum now.
We must act -together, urgently, and visibly.
Next Steps
Here is what we do not know
Whether APOLLO results will fully meet the FDA’s threshold for demonstrating clinical benefit.
Whether the FDA will request additional analyses or studies beyond APOLLO.
If the bitopertin resubmission will be reviewed as part of the Commissioner’s National Priority Voucher (CNPV) pilot program.
What can you do?
If you are participating in APOLLO, complete all study tasks—your data is essential (and thank you!).
Use your voice publicly: call on the FDA and your legislators to apply the regulatory flexibility granted for rare diseases.
Share your story on this website and on social media to raise visibility and urgency.
Report from the February 17, 2026 UPA EPP/XLP Community Call
To help our community understand the FDA's decision and what comes next, UPA hosted a community call with Disc Medicine CEO John Quisel, regulatory expert James Valentine and porphyria expert Dr. Amy (Dickey) Yeung.
Key takeaways:
The FDA agreed that bitopertin is effective at lowering protoporphyrin IX, but would like to see more evidence that makes a difference to the amount of sun exposure
Additional data is already being collected through the phase 3 APOLLO study
Disc Medicine is meeting with the FDA to ensure they are on track
If you are a trial participant, please be sure to complete all study related tasks to ensure the APOLLO study has complete data!