Figure 3 Genetics of erythropoietic protoporphyria (EPP) and relationship between genotype and ferrochelatase activity (expressed as a percentage of normal). (A) Autosomal recessive inheritance. (B) Autosomal dominant inheritance due to co‐inheritance of low‐expression and mutant alleles. FECH, ferrochelatase; N, normal ferrochelatase gene; M, mutant allele; n, low‐expression allele.