Harderoporphyria is a rare disorder of heme biosynthesis, inherited in an autosomal recessive manner caused by specific mutations in the CPOX gene.

[2] In contrast with other porphyrias, which typically present with either cutaneous lesions after exposure to sunlight or acute neurovisceral attack at any age (most commonly in adulthood), harderoporphyria is characterized by jaundice, anemia enlarged liver and spleen, often presenting in the neonatal period.

Later in life, these individuals may present with photosensitivity similar to that found in cutaneous porphyrias.

[2] Biochemically, harderoporphyria presents with a distinct pattern of increased harderoporphyrin (2-vinyl-4,6,7-tripropionic acid porphyrin)[3] in urine and particularly in feces, a metabolite that is not seen in significant quantities in any other porphyria.

[2] Enzyme tests show markedly reduced activity of coproporphyrinogen oxidase, compared to both unaffected individuals and those affected with hereditary coproporphyria, consistent with recessive inheritance.