Start with the molecule, because the molecule really is the story here. The human body makes a compound called protoporphyrin IX, which does various jobs. In people with erythropoietic protoporphyria, or EPP, a genetic mutation means the body makes far too much of it, and the excess collects in the skin, where it is activated by sunlight. The result, for the sufferer, is that a few minutes outdoors — walking to the car, pumping gas — can produce burning pain that lasts for days. If you were designing a treatment from first principles, there is roughly one idea available: get the patient to carry less of the molecule. A once-daily pill called bitopertin does exactly that, and it is now moving through human clinical trials in the United States. CBS News has the story of one of its trial patients, and hers is about as clear an illustration of the arithmetic as you could ask for.
Emily Pearson was 8 years old when the attacks started. Minutes in the sun left her hands and feet feeling, she told CBS News, like they were “in a hot oven” while being poked “with pins and needles.” A decade of uncertainty followed: sunblock didn’t help, so she wore protective clothing, stayed indoors, and treated the family vacations at a Minnesota cabin as endurance tests. At 17, a doctor at the Mayo Clinic in Rochester diagnosed EPP. Having an answer was a relief, she said — but it also meant accepting there wasn’t much that could be done. “It was just insufferable pain. I would never wish that pain upon anyone, because it’s so horrible,” said Pearson, who lives in Minneapolis.
Her outlet was running — half-marathons, logged at sunrise or after dark or under layers of protective gear. A full marathon, she assumed, was out of the question. “Going to the grocery store, going to get gas, going for any kind of car ride or working outside, you constantly have to think about what you’re doing and how it’s going to affect your health, and dealing with those consequences after,” Pearson, now 25, said. “It was a big mental load, and it was never-ending.”
The turning point came in 2025, when she volunteered at Sun Escape, a weekend camp for children with EPP and similar conditions, and heard about the bitopertin trial. Her reaction was the rational one, she recalled: “Does it really work? I know it works for other people, but will it work for me?” There was, she said, “that anxiety of the unknown.”
She enrolled in the trial’s second phase — the stage, under the U.S. Food and Drug Administration’s four-phase framework, where up to several hundred patients take a drug for months or years so researchers can measure both its effectiveness and its side effects, after Phase 1 has established safety and dosing and before Phases 3 and 4 expand to larger populations and the FDA weighs approval. Pearson began taking bitopertin daily in July 2025, with regular appointments with physicians in Boston. Within weeks, she said, she was doing “really, really well,” and her tolerance of the sun started rising.
That matches what Dr. Sioban Keel, a porphyria expert at the University of Washington who is involved in the trial — though she did not treat Pearson — told CBS News she has heard from other patients. “The impact I’ve seen it have on my patients has been a game changer. Patients that previously could never go out in the sun are able to go out in the sun ... You’re like, ‘I can’t believe I’m hearing this.’” Clinical trial data released in April by Disc Medicine, the drug’s developer, said bitopertin “significantly reduced protoporphyrin-IX levels,” produced “improved measures of sunlight tolerance” in EPP patients and raised “no notable safety concerns.”
Bitopertin is now in Phase 3, with 183 patients enrolled and data expected in the final quarter of 2026. The path to market is not frictionless: the FDA has declined to review the drug for expedited approval, saying in effect that it wants more evidence of the benefit to patients, according to a written statement from Disc Medicine. The company says it believes the Phase 3 data will supply what the agency asked for. Pearson, meanwhile, stays on the drug through an open-label extension — the optional phase where trial patients are offered the choice to continue taking it.
Which is where the denominator of this story changes. In October 2025, about three months after starting the pill, Pearson ran her first marathon. “I was outside the whole day, running and having fun,” she said. “I just got to wear shorts and a T-shirt.” She ran another marathon this June, then spent a July week at the family cabin — a trip that used to be what she calls a source of anxiety — “outside every day, sunup to sundown, no reactions.” She still sometimes feels minor reactions after long stretches outdoors, she noted, but the pain is far less and her tolerance far higher. “Now, I had the best week ever,” she said.
Next up: another marathon in June 2027, and possibly a triathlon, reviving her old life as a competitive swimmer. “I’m able to feel free and live without all the worry and anxiety that I was before,” she said. “I’m 20 times happier. I’m more energetic. My life has literally changed so much.”
The FDA, reasonably, would like a larger sample than one delighted Minnesotan before calling bitopertin a proven drug, and Phase 3 exists precisely to convert anecdotes into statistics. The statistics are coming. The shorts and T-shirt are already out of the drawer.