Emily Pearson was diagnosed at 17 with erythropoietic protoporphyria (EPP), a rare condition that causes severe pain after sun exposure. She joined a Phase 2 trial of bitopertin in July 2025 and reported rapid improvement in sunlight tolerance, enabling her to run marathons and enjoy extended outdoor time. Disc Medicine reported reduced protoporphyrin-IX levels and improved sunlight tolerance with no notable safety concerns; bitopertin moved into Phase 3 with 183 patients enrolled and data expected in Q4 2026. The FDA has requested additional patient-impact data before expedited review.
Clinical Trial Drug Restores Sunlight Freedom for Woman With Rare Photosensitivity
Emily Pearson runs in layers. / Credit: Emily Pearson
Emily Pearson developed debilitating, sun-triggered pain at age eight that left her hands and feet burning and numb for days. For years doctors were unable to explain the episodes, until a Mayo Clinic diagnosis at 17 identified erythropoietic protoporphyria (EPP), a rare disorder that causes extreme sensitivity to sunlight.
Sun protection and lifestyle changes helped, but severely limited her life. Pearson avoided daytime runs, layered clothing, and largely stayed indoors. Running remained a refuge she treasured, but she believed a full marathon was out of reach.
Emily Pearson in protective gear. / Credit: Emily Pearson
Hope From a Clinical Trial
In 2025, while volunteering at Sun Escape — a camp for children with EPP and related disorders — Pearson learned about a clinical trial for a drug called bitopertin. She enrolled in the Phase 2 study and began taking the pill daily in July 2025, with regular follow-ups at clinical sites in Boston.
“It was just insufferable pain. I would never wish that pain upon anyone,” Pearson said. After starting the trial, she added: “Within weeks I started feeling really, really well.”
What Bitopertin Does
Experts involved in the trial explain that bitopertin lowers levels of protoporphyrin IX, a naturally occurring molecule in the skin that becomes reactive when exposed to sunlight. In people with EPP, genetic mutations cause excessive protoporphyrin IX, producing painful reactions on sun exposure. Disc Medicine reported in April that bitopertin "significantly reduced protoporphyrin-IX levels" and led to "improved measures of sunlight tolerance" with no notable safety concerns in available data.
Emily Pearson runs her first marathon. / Credit: Emily Pearson
Trial Status and Regulatory Context
Bitopertin advanced to Phase 3 trials with 183 patients enrolled; full data were expected in Q4 2026. The U.S. Food and Drug Administration declined to consider the drug for expedited approval, requesting additional evidence of patient-level benefit. Disc Medicine has said it expects the Phase 3 data to address the agency's questions.
Life Changes and Ongoing Follow-Up
Pearson continues on the drug through an open-label extension. Her tolerance for sunlight has improved markedly: she completed her first marathon in October 2025, ran another in June (year stated in the trial account), and spent an entire week at her family’s Minnesota cabin in July without the severe reactions that once ruined vacations. She still reports occasional mild symptoms after prolonged exposure, but overall pain and anxiety have dropped substantially.
Emily Pearson, in pink shorts, after running her first marathon. / Credit: Emily Pearson
“I was outside the whole day, running and having fun… I’m 20 times happier. I’m more energetic. My life has literally changed so much,” Pearson said.
Looking Ahead
Pearson plans to run another marathon in June 2027 and hopes to train for a triathlon. While larger Phase 3 results and regulatory review will determine whether bitopertin becomes widely available, the drug has given trial participants — and Pearson in particular — a glimpse of life with far fewer limits from EPP.
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