Porphyria caused by monoallelic and biallelic variants in UROD and presenting as a spectrum of disease (a semidominant inheritance pattern). Additionally, environmental factors almost always play a role in the disease. Monoallelic variants when exacerbated by environmental factors can result in episodic adult onset of photosensitivity. Biallelic variants that reduce WT enzyme activity <20% cause childhood onset of photosensitivity and sometimes liver damage.