Patients with EPP who develop liver disease usually have a mutation in one ferrochelatase allele that alters enzyme function, together with a polymorphism in the nonmutant allele that causes low gene expression.
Furthermore, no significant association of the liver complication with the location of the mutation within the FECH gene was found (Fisher exact test p = 0.46).
The mutant phenotype, which shows light-dependent hemolysis and liver disease, is similar to that seen in humans with erythropoietic protoporphyria, a disorder of ferrochelatase.
Erythropoietic protoporphyria (EPP) is a rare autosomal dominant disorder of heme biosynthesis characterized by partial decrease in ferrochelatase (FECH; EC 4.99.1.1) activity with protoporphyrin overproduction and consequent painful skin photosensitivity and rarely liver disease.