PFIC is a rare genetic disorder that causes progressive liver disease, which typically leads to liver failure. The disease is inherited in an autosomal recessive pattern, meaning mutations in both copies of the gene are necessary to cause the disorder. The disease is estimated to affect one in every 50,000 to 100,000 births in the United States and Europe, and we estimate that there are approximately 3,000 patients with PFIC in the United States and approximately 5,000 in Europe.
In patients with PFIC, liver cells have a diminished ability to secrete bile due to mutations in proteins that control bile flow. The resulting buildup of bile in liver cells causes liver damage in affected individuals. Six types of PFIC have been genetically identified, all of which are similarly characterized by impaired bile flow and progressive liver disease. Our initial focus is on the PFIC2 patient population, which accounts for approximately 60% of the PFIC patient population. PFIC2 is caused by a mutation in the ABCB11 gene, which normally encodes a bile salt export pump, or BSEP, protein that transports bile acids out of the liver. Mutations in the ABCB11 gene result in the buildup of bile salts in liver cells, damaging these cells and causing liver disease.
Signs and symptoms of PFIC typically begin in infancy and are related to buildup of toxic bile acid in the liver. Patients with PFIC experience pruritus, jaundice, failure to gain weight and to grow at the expected rate, enlarged livers and spleens and progressive liver disease. Elevation of sBA is a common feature of the disease. Children with PFIC2 often develop liver failure within the first few years of life and have an increased risk of developing liver cancer. The most prominent and troublesome ongoing symptom of PFIC is severe pruritus, leading to a greatly diminished quality of life.
There remains a substantial unmet medical need for therapeutic options for PFIC, as PEBD and liver transplantation are often the sole options available for patients. Children with PFIC2 are our initial target patient population for treatment with maralixibat. We believe the opportunity exists to broaden beyond this initial patient population, and we plan to evaluate the effectiveness of maralixibat in patients with other types of PFIC, such as PFIC1 and PFIC3, in a supplemental cohort in our Phase 3 MARCH trial.
Benign recurrent intrahepatic cholestasis, or BRIC, consists of two types, BRIC1 and BRIC2, which have the same underlying genetic mutations as PFIC1 and PFIC2, respectively. BRIC is characterized by intermittent episodes of cholestasis with pruritus. This condition is called benign because it typically does not cause lasting damage to the liver, but it can develop into a more severe, permanent form. There are no approved therapies for BRIC, but patients can achieve temporary relief of the severe pruritus by lowering bile acid levels through procedures such as naso-biliary drainage. We believe there is therapeutic potential for an ASBT inhibitor, or ASBTi, for the treatment of pruritus associated with BRIC.