While approximately 4% of EPP patients carry two uncommon pathogenic FECH variants, the typical molecular abnormality found in around 96% of EPP patients involves a rare pathogenic FECH variant alongside a common intronic FECH variant known as c.315-48T>C (also historically referred to as IVS3-48T>C). Here, FECH is linked to autosomal erythropoietic protoporphyria.