NIH

Zebra of the Week: Erythropoietic protoporphyria

February 19, 2026

Erythropoietic protoporphyria (EPP) is a rare congenital metabolic disorder characterized by an inborn error of porphyrin–heme biosynthesis. Clinically, EPP is defined by painful cutaneous photosensitivity that can lead to blistering and scarring of sun‑exposed skin. Additional associated findings include erythrodontia, red discoloration of urine, hemolytic anemia, and splenomegaly. Because symptom onset timing is not well‑defined and presentations are variable, EPP can be diagnostically challenging.

FDA recently issued a complete response letter (CRL) for bitopertin, an investigational treatment for EPP, delaying approval pending results from the phase 3 APOLLO trial (NCT06910358).

Sources:

(Accessed 2026, February 18). NIH Genetic and Rare Diseases Information Center (GARD). Erythropoietic protoporphyria. https://rarediseases.info.nih.gov/diseases/7476/erythropoietic-protoporphyria

(2026, February 13). Disc Medicine. Disc Medicine Receives Complete Response Letter from FDA for Bitopertin for the Treatment of EPP [News release]. https://ir.discmedicine.com/news-releases/news-release-details/disc-medicine-receives-complete-response-letter-fda-bitopertin