Effect of Bitopertin on the Liver and on Levels of Protoporphyrin IX in Bile, Blood, Liver, and Stool in Patients With Erythropoietic Protoporphyria/X-linked Protoporphyria and Increased Liver Stiffness and/or Liver Enzymes at Baseline

Inclusion Criteria: * Diagnosis of EEP or XLP that has been biochemically and genetically verified prior diagnosis of EPP or XLP * Age 18-75 years * Increased liver stiffness at baseline, defined as stiffness measurement \[E value\] by: Fibroscan \>7 kPa; MRE that is \>3.0 kPa; Velacur/Sonicincyte that is \>6.0 kPa; and/or elevated liver enzymes: serum ALT \> 2 X upper limit of normal (ULN), but not greater than 5 X ULN and/or serum AP \> 2 X ULN, but not greater than 5 X ULN * INR \< 1.4 * Compensated liver disease at baseline, defined as lack of clinically evident ascites, encephalopathy, hepatocellular carcinoma, clinically evident icterus or jaundice, peripheral edema. * Willingness and ability to volunteer and provide informed consent for a long-term study that will include liver biopsies and collection of bile from the second portion of the duodenum, at baseline and at the end of study. In addition, follow-up visits will be planned every 26 weeks throughout the study, with plans for repeat routine/safety labs at each visit and for measures of liver stiffness and markers of hepatic status and fibrosis (Fib-4, APRI, ELF, Fibrotest) performed once every 6 months. Exclusion Criteria: * Chronic hepatitis B, C, D, or E; * Human immunodeficiency (HIV) infection; * Alcohol use \> 14 units/week for men or \> 7 units/week for women; * Pregnancy or breast feeding among women; * Any known active malignancy other than small and localized squamous or basal cell carcinoma of the skin; * Advanced or decompensated heart, lung, kidney, liver, or neuro-psychiatric disease; * History of diagnosed depression or suicidality; * History of diagnosed substance abuse or poor impulse control; * Any other conditions that, in the opinion of the Investigator, renders the individual unfit to participate