Porphyria attacks were defined as meeting all of the following criteria: an acute episode of neurovisceral pain in the abdomen, back, chest, extremities and/or limbs, no other medically determined cause, and required treatment with intravenous (IV) dextrose or hemin, carbohydrates, or analgesics, or other medications such as antiemetics at a dose or frequency beyond the participant's usual daily porphyria management. The annualized rate of porphyria attacks is a composite endpoint which included porphyria attacks requiring hospitalization, urgent healthcare visit, or IV hemin administration at home.