Disc Medicine said its GlyT1 inhibitor bitopertin cleared both co-primary endpoints in the Phase 3 APOLLO study for erythropoietic protoporphyria, addressing concerns it previously faced about efficacy biomarkers. The update follows scrutiny of earlier biomarker results, which Disc argued did not reflect meaningful clinical benefit. In APOLLO, bitopertin reduced whole-blood protoporphyrin IX pathway activity—measured as PPIX—by 41.4% versus placebo (p<0.0001) and increased average monthly time in light without pain by 12.2 hours at month six (p=0.001). The company reported the results sent shares up sharply after the readout. For investors and clinicians, the key next step is how regulators will weigh the clinical endpoints versus earlier biomarker uncertainty. The Phase 3 success also repositions Disc’s program as competitors have faced major setbacks in their own late-stage readouts.