Progressive familial intrahepatic cholestasis

Other names:ABCB4-related intrahepatic cholestasis;ABCB11-related intrahepatic cholestasis;ATP8B1-related intrahepatic cholestasis;BSEP deficiency;Byler disease;Byler syndrome;FIC1 deficiency;low γ-GT familial intrahepatic cholestasis;MDR3 deficiency

Progressive familial intrahepatic cholestasis (PFIC) is a disorder that causes progressive liver disease, which typically leads to liver failure. In people with PFIC, liver cells are less able to secrete a digestive fluid called bile. The buildup of bile in liver cells causes liver disease in affected individuals.

Epidemiology

PFIC is estimated to affect 1 in 50,000 to 100,000 people worldwide. PFIC type 1 is much more common in the Inuit population of Greenland and the Old Order Amish population of the United States.

Types

There are three known types of PFIC: PFIC1, PFIC2, and PFIC3. The types are also sometimes described as shortages of particular proteins needed for normal liver function. Each type has a different genetic cause.

Cause

Mutations in the ATP8B1, ABCB11, and ABCB4 genes can cause PFIC.

ATP8B1 gene mutations cause PFIC1. The ATP8B1 gene provides instructions for making a protein that helps to maintain an appropriate balance of bile acids, a component of bile. This process, known as bile acid homeostasis, is critical for the normal secretion of bile and the proper functioning of liver cells. In its role in maintaining bile acid homeostasis, some researchers believe that the ATP8B1 protein is involved in moving certain fats across cell membranes. Mutations in the ATP8B1 gene result in the buildup of bile acids in liver cells, damaging these cells and causing liver disease. The ATP8B1 protein is found throughout the body, but it is unclear how a lack of this protein causes short stature, deafness, and other signs and symptoms of PFIC1.

Mutations in the ABCB11 gene are responsible for PFIC2. The ABCB11 gene provides instructions for making a protein called the bile salt export pump (BSEP). This protein is found in the liver, and its main role is to move bile salts (a component of bile) out of liver cells. Mutations in the ABCB11 gene result in the buildup of bile salts in liver cells, damaging these cells and causing liver disease.

ABCB4 gene mutations cause PFIC3. The ABCB4 gene provides instructions for making a protein that moves certain fats called phospholipids across cell membranes. Outside liver cells, phospholipids attach (bind) to bile acids. Large amounts of bile acids can be toxic when they are not bound to phospholipids. Mutations in the ABCB4 gene lead to a lack of phospholipids available to bind to bile acids. A buildup of free bile acids damages liver cells and leads to liver disease.

Some people with PFIC do not have a mutation in the ATP8B1, ABCB11, or ABCB4 gene. In these cases, the cause of the condition is unknown.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

Signs and symptoms of PFIC typically begin in infancy and are related to bile buildup and liver disease. Specifically, affected individuals experience severe itching, yellowing of the skin and whites of the eyes (jaundice), failure to gain weight and grow at the expected rate (failure to thrive), high blood pressure in the vein that supplies blood to the liver (portal hypertension), and an enlarged liver and spleen (hepatosplenomegaly). In addition to signs and symptoms related to liver disease, people with PFIC1 may have short stature, deafness, diarrhea, inflammation of the pancreas (pancreatitis), and low levels of fat-soluble vitamins (vitamins A, D, E, and K) in the blood. Affected individuals typically develop liver failure before adulthood.

The signs and symptoms of PFIC2 are typically related to liver disease only; however, these signs and symptoms tend to be more severe than those experienced by people with PFIC1. People with PFIC2 often develop liver failure within the first few years of life. Additionally, affected individuals are at increased risk of developing a type of liver cancer called hepatocellular carcinoma.

Most people with PFIC3 have signs and symptoms related to liver disease only. Signs and symptoms of PFIC3 usually do not appear until later in infancy or early childhood; rarely, people are diagnosed in early adulthood. Liver failure can occur in childhood or adulthood in people with PFIC3.

Diagnosis

Biochemical markers include a normal GGT for PFIC-1 and -2, with a markedly elevated GGT for PFIC-3. Serum bile acid levels are grossly elevated. Serum cholesterol levels are typically not elevated, as is seen usually in cholestasis, as the pathology is due to a transporter as opposed to an anatomical problem with biliary cells.

PFIC1 should be suspected in children with a clinical history of cholestasis of unknown origin after exclusion of the other main causes of cholestasis presenting with normal serum gamma-GT activity and high serum bile acid concentration. Usually, serum alpha-fetoprotein level is normal and alanine aminotransferase values are below five times the upper limit of normal.

Liver ultrasonography is usually normal but may reveal a huge gallbladder. Liver histology reveals canalicular cholestasis and the absence of true ductular proliferation with only periportal biliary metaplasia of hepatocytes. When performed, cholangiography shows a normal biliary tree and allows bile collection. Biliary lipid analysis reveals mildly decreased biliary bile salt concentration. Genotyping confirms the diagnosis.

Treatment

Ursodeoxycholic acid therapy (UDCA) should be initiated in all patients to prevent liver damage but is not fully effective. Rifampicin is helpful to control pruritus. Nasobiliary drainage may help to select potential responders to biliary diversion. However, because of severe cholestasis, half of patients are ultimately candidates for liver transplantation (LT). Diarrhea often worsens after LT and might be favorably managed by bile adsorptive resin treatment. LT does not prevent extrahepatic progression of the disease, and does not lead to catch-up growth. Furthermore, severe steatohepatitis of the liver graft has been reported. Specialized follow-up is mandatory lifelong. FIC1 defect predisposes to development of intrahepatic cholestasis of pregnancy.

Prognosis

The disease is typically progressive, leading to fulminant liver failure and death in childhood, in the absence of liver transplantation. Hepatocellular carcinoma may develop in PFIC-2 at a very early age; even toddlers have been affected.

NIH genetic and rare disease info

• NIH info on Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis is a rare disease.

Progressive familial intrahepatic cholestasis Resources
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