Approximately 95% of patients with EPP have a rare, pathogenic missense, nonsense, spliced, or deleted FECH allele in trans of a common intronic variant c.315-48T>C (rs2272783) that increases the use of an aberrant splice site, resulting in a premature stop codon (Figure 1A). This evidence concerns the gene FECH and autosomal erythropoietic protoporphyria.