JAMA Dermatol 153 (8): 789 - 796, 2017. doi: 10.1001 / jamadermatol.2017.1557 Diagnosis Red blood cell and plasma protoporphyrin measurement Genetic testing for FECH or ALAS 2 gene mutations Erythropoietic protoporphyria or X-linked protoporphyria should be suspected in children and adults with painful cutaneous photosensitivity who experience no blisters or scarring.