Inherited disorders associated with conjugated hyperbilirubinemia

INTRODUCTION — 

Conditions that cause hyperbilirubinemia can be classified into those that result in a predominantly unconjugated hyperbilirubinemia and those that are associated with an elevation of both conjugated and unconjugated forms of bilirubin. (See "Classification and causes of jaundice or asymptomatic hyperbilirubinemia".)

This topic review will discuss inherited disorders associated with conjugated hyperbilirubinemia, especially Dubin-Johnson syndrome and Rotor syndrome. More commonly, conjugated hyperbilirubinemia is caused by an acquired condition, such as alcohol-related hepatitis, viral hepatitis, biliary obstruction, or cholestasis of pregnancy, which are discussed separately.

CLASSIFICATION — 

Several different inherited disorders are characterized by impaired elimination of conjugated bilirubin, with or without impaired excretion of other organic anions. They are caused by pathogenic variants in the following genes [1]:

●Dubin-Johnson syndrome – ABCC2 (MRP2) (see 'Dubin-Johnson syndrome' below)

●Rotor syndrome – SLCO1B1 and SLCO1B3 (coincident pathogenic variants) (see 'Rotor syndrome' below)

●Progressive familial intrahepatic cholestasis (PFIC):

•PFIC type 1 (FIC1 deficiency) – ATP8B1 (see 'PFIC type 1 (FIC1 deficiency)' below)

•PFIC type 2 (bile salt export pump [BSEP] deficiency) – ABCB11 (see 'PFIC type 2 (BSEP deficiency)' below)

•PFIC type 3 (multidrug resistance protein-3 P-glycoprotein [MDR3] deficiency) – ABCB4 (see 'PFIC type 3 (MDR3 deficiency)' below)

•Other forms of PFIC (see 'Other forms of PFIC' below)

●PFIC-related cholestatic phenotypes (see 'Related disorders' below):

•Benign recurrent intrahepatic cholestasis (BRIC)

•Low phospholipid-associated cholestasis syndrome (LPAC)

●Alagille syndrome – JAG1 or NOTCH2 (see "Alagille syndrome")

Dubin-Johnson syndrome and Rotor syndrome have similar phenotypes (mild fluctuating elevation of both unconjugated and conjugated bilirubin in plasma). However, in Dubin-Johnson syndrome, the biliary excretion of organic anions (except bile acids) is impaired, while Rotor syndrome is a disorder of reuptake of bilirubin glucuronides. Other inherited conditions such as PFIC and BRIC cause conjugated hyperbilirubinemia as a consequence of reduced bile flow and are therefore associated with biochemical cholestasis [1].

DUBIN-JOHNSON SYNDROME — 

Dubin-Johnson syndrome (MIM #237500) is a benign inherited disorder characterized by impaired bilirubin excretion from the hepatocyte and mild fluctuating conjugated hyperbilirubinemia. The disorder occurs in males and females of all races and nationalities [2-5]. It is rare, except in Sephardic Jews, in whom the incidence is approximately 1:3000 [5].

Clinical features — Dubin-Johnson syndrome is characterized clinically by mild icterus, without pruritus. Otherwise, patients are asymptomatic, although some have mild constitutional complaints such as vague abdominal pains and weakness. The physical examination is usually normal except for the icterus, although hepatosplenomegaly is occasionally noted [6-8]. The icterus can be so mild as to be noted only during intercurrent illnesses, pregnancy, or consumption of oral contraceptives [4]. This disorder is often first diagnosed during adolescence or adulthood but occasionally presents with neonatal cholestasis, with favorable outcomes [9,10].

During pregnancy, serum bilirubin levels may be further elevated, requiring differentiation from cholestasis of pregnancy. The latter is usually associated with pruritus, which is not a feature of Dubin-Johnson syndrome [11]. (See "Intrahepatic cholestasis of pregnancy".)

Reduced prothrombin activity, resulting from lower levels of clotting factor VII, is found in 60 percent of patients with Dubin-Johnson syndrome. Factor VII deficiency is most common among Sephardic Jews originating from Iran, Iraq, and neighboring areas [12-14]. However, reduced factor VII levels are also found among patients from other communities. In some families, the two disorders segregate independently, indicating that the linkage is not tight.

Altered drug metabolism — The causative gene ABCC2 (MRP2) has a large number of substrates, including endogenous metabolites, drugs, and other xenobiotics [15], which may have consequences in the their pharmacokinetics. Although these interactions are weak and the information is mostly based on small studies or case reports, caution should be used when using certain drugs in each of the following categories, including:

●Human immunodeficiency virus (HIV) protease inhibitors – eg, tenofovir, indinavir (but not nelfinavir).

●Antibiotics – eg, erythromycin, rifampin.

●Antiepileptic drugs – eg, carbamazepine, valproic acid.

●Nonsteroidal antiinflammatory drugs – eg, ibuprofen, naproxen, salicylates.

●Anticancer agents – eg, methotrexate, tamoxifen, docetaxel, irinotecan, vincristine (but not doxorubicin) [16]. Case reports describe the association of ABCC2 variants with reduced clearance of methotrexate [17] and vincristine [18] that required dose reduction.

Laboratory tests

●Routine laboratory tests – Serum bilirubin concentrations are usually between 2 and 5 mg/dL (34 to 85 micromol/L) but may decline to normal levels or be as high as 20 to 25 mg/dL (340 to 2125 micromol/L). Approximately 50 percent of the serum bilirubin is conjugated. In addition, covalently albumin-bound fraction is found in plasma. Bilirubinuria is common.

Other routine clinical laboratory tests, including complete blood count, serum albumin, cholesterol, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, and prothrombin time, are normal [3-5] (except in patients who have coexistent factor VII deficiency (see 'Clinical features' above)) [12-14]. Fasting and postprandial bile acid levels, which are sensitive indices of liver disease, are also normal, reflecting the fact that the genetic abnormality does not affect the transport of most bile acids.

●Urinary coproporphyrin excretion – Quantification and fractionation of urinary coproporphyrin are practical approaches to diagnosing Dubin-Johnson syndrome and distinguishing it from Rotor syndrome. In Dubin-Johnson syndrome, total urinary coproporphyrin is normal (20 to 120 mcg/L [25 to 144 nmol/L]). However, over 80 percent of it is coproporphyrin I, in contrast with the general population, in which 75 percent of urinary coproporphyrin is coproporphyrin III [19-21]. By contrast, in Rotor syndrome, urinary coproporphyrin is greatly increased and coproporphyrin I is approximately 65 percent of the total (see 'Differentiation of Rotor syndrome from Dubin-Johnson syndrome' below). Chromatographic analysis of coproporphyrins can be obtained from frozen urine from ARUP Laboratories (Utah), Labor Berlin laboratory (Germany), and Laboratory of the University Hospital in Maastricht (Netherlands).

●Genetic testing – Dubin-Johnson syndrome is caused by pathogenic mutations in the ABCC2 gene, including gene deletions, nonsense or missense mutations, mutations affecting messenger ribonucleic acid (mRNA)-microRNA interactions, as well as exonic splice site mutations [6-8,22]. (See 'Molecular mechanisms' below.)

If urinary coproporphyrin analysis does not provide a firm diagnosis, genetic testing can confirm the diagnosis of Dubin-Johnson syndrome and distinguish it from Rotor syndrome. This can be accomplished with next-generation sequencing panels for cholestatic liver diseases. Although whole-exome sequencing would identify most of these gene variants [6,7], identication of intronic splice site mutation requires whole-genome sequencing [23]. A list of tests and laboratories is available at the Genetic Testing Registry.

●Imaging – The gallbladder is normal on ultrasonography. Oral cholecystography, using even a double dose of contrast material, is unsuccessful in visualizing the biliary system. However, the biliary system may be visualized on delayed views, four to six hours after intravenous administration of iodipamide [24,25]. Computed tomography of patients with Dubin-Johnson syndrome shows greater attenuation in the liver compared with the general population [26].

●Pathology – Grossly, the liver is black [2]. It is histologically normal, except for the presence of a dense pigment (picture 1). Electron microscopy reveals that the pigment is contained in the lysosomes [27]. Electron spin resonance spectroscopy suggests that the pigment is composed of polymers of epinephrine metabolites [28].

Diagnosis — Dubin-Johnson syndrome should be suspected in patients with mild conjugated hyperbilirubinemia in the absence of other abnormalities of standard liver tests (serum ALT, AST, alkaline phosphatase, gamma-glutamyl transpeptidase [GGTP], albumin, and prothrombin time).

The diagnosis of Dubin-Johnson syndrome is established by analysis of urinary coproporphyrin excretion (normal total coproporphyrin with elevated coproporphyrin I); this test also distinguishes it from Rotor syndrome (algorithm 1). Alternatively, genetic testing can be used to establish the diagnosis of Dubin-Johnson syndrome and distinguish it from Rotor syndrome. (See 'Laboratory tests' above and 'Differentiation of Rotor syndrome from Dubin-Johnson syndrome' below.)

Although Dubin-Johnson syndrome and Rotor syndrome are generally considered benign, making a definitive diagnosis is valuable because of the associated differences in drug metabolism. In addition, when Dubin-Johnson syndrome presents in the neonatal period, it must be distinguished from other causes of conjugated hyperbilirubinemia, such as biliary atresia [9,10]. In cases where Dubin-Johnson syndrome first presents during pregnancy, it should be distinguished from other causes of cholestasis of pregnancy [11].

Management — Dubin-Johnson syndrome is a benign condition, and no treatment is required. However, it is important to recognize the condition so as not to confuse it with other hepatobiliary disorders associated with conjugated hyperbilirubinemia. Also, it may be useful to establish or exclude Dubin-Johnson syndrome in patients with mildly elevated serum bilirubin levels because several drugs may require dose adjustment in this condition. (See 'Altered drug metabolism' above.)

Molecular mechanisms

●Genetics – Dubin-Johnson syndrome is caused by homozygosity or compound heterozygosity of pathogenic variants in the ABCC2 gene, which encodes the multidrug resistance related protein, MRP2 (also known as the canalicular multispecific organic anion transporter [cMOAT]) (figure 1) [29-33]. MRP2 transports nonbile acid organic anions, such as conjugated bilirubin and other glucuronidated, sulfated, or glutathione conjugated substances, from the hepatocyte into the bile canaliculus against a high concentration gradient. MRP2 is one of the adenosine triphosphate (ATP)-binding cassette transporters, which derive the energy from ATP hydrolysis [34].

The electrochemical gradient created by the negative intracellular potential (-35 mV) also contributes to the transport of bilirubin glucuronides into the bile canaliculus [35-37]. This explains why the syndrome is associated with relatively mild hyperbilirubinemia despite the marked reduction or absence of ABBC2 function.

Dubin-Johnson syndrome has been associated with 130 causative mutations within the ABCC2 gene, as listed in the Human Gene Mutation Database (figure 2) [7,38-49]. The pathogenic variants may interfere with ATP binding [39,41], impair protein maturation, or cause mislocalization of the protein (mutation "h" in the figure) (figure 2) [50]. A case report identified a variant at an intronic splice donor site [42]. Autosomal recessive inherence has been confirmed based on urinary coproporphyrin analysis in families of affected individuals [51,52].

●Clearance of bromsulphthalein (BSP) and other organic anions – Plasma clearance of intravenously administered BSP has a characteristic pattern in Dubin-Johnson syndrome, but this test is not used for clinical diagnosis. If it is performed, plasma clearance of BSP is greatly delayed [53,54] and there is a secondary rise in serum BSP approximately 90 minutes after BSP administration. Although the secondary rise is characteristic of Dubin-Johnson syndrome, it is not diagnostic by itself, because it is also seen in hepatobiliary cholestatic disorders.

●Animal models – The substrates of MRP2 have been characterized extensively in the most widely used model, the TR-rat [15,36,55-58]. In these rats, biliary excretion of conjugated bilirubin and other organic anions is impaired. The predominant coproporphyrin in urine is coproporphyrin I [19]. Other animal models are the Corriedale sheep (in which urinary coproporphyrin excretion patterns are similar to those of Dubin-Johnson syndrome, and lysosomal accumulation of black pigments in the liver occurs when the sheep are fed a diet enriched with amino acids [55]) and the golden lion tamarin monkey [59].

ROTOR SYNDROME — 

Rotor syndrome is a rare autosomal recessive disorder characterized by mild conjugated and unconjugated hyperbilirubinemia. It has been reported in small case series from multiple countries around the world [60].

Clinical features — Rotor syndrome is a benign condition characterized by chronic fluctuating conjugated and unconjugated hyperbilirubinemia without evidence of hemolysis [61]. Although this serologic phenotype is similar to Dubin-Johnson syndrome, Rotor syndrome involves impaired hepatic reuptake of conjugated bilirubin. By contrast, Dubin-Johnson syndrome is characterized by impaired biliary excretion of organic anions.

Altered drug metabolism — Rotor syndrome is caused by simultaneous inherited abnormalities of organic anion transporter proteins 1B1 and 1B3 (OATP1B1 and OATP1B3). Although Rotor syndrome is generally benign, affected individuals are at risk for serious drug toxicities from certain commonly used drugs that are substrates of one or both of these transporters (table 1) [62-65]. Therefore, great caution should be used in treating people with Rotor syndrome with drugs that undergo transport by these proteins. Individuals with reduced activity of only one of these transporter proteins also may be at increased risk for drug toxicities, although they do not have jaundice. (See 'Molecular mechanisms' below.)

Laboratory tests

●Standard laboratory tests – Serum total bilirubin usually ranges from 2 to 5 mg/dL (34 to 85 mmol/L) with over 50 percent direct-reacting (conjugated) fraction. Serum alkaline phosphatase, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transpeptidase (GGTP) levels are normal. Serum bile acid levels may be mildly elevated because of the retention of bile acid 3-C glucuronides [66].

●Urinary coproporphyrin excretion – Measurement of urinary coproporphyrin is a practical approach to diagnosing Rotor syndrome and distinguishing it from Dubin-Johnson syndrome. In individuals with Rotor syndrome, total urinary coproporphyrin excretion is increased to 250 to 500 percent of normal (where the normal range is 20 to 120 mcg/L [25 to 144 nmol/L]) and coproporphyrin I constitutes approximately 65 percent of urinary porphyrins [67,68]. In obligate heterozygotes, the pattern of excretion is intermediate between that of patients with Rotor syndrome and controls. The pattern of coproporphyrin excretion is distinct from that of Dubin-Johnson syndrome [68], although this pattern may also be found in inherited or acquired cholestatic diseases. (See 'Differentiation of Rotor syndrome from Dubin-Johnson syndrome' below.)

●Genetic testing – Rotor syndrome is a digenic ressesive disorder caused by coexistent genetic abnormalities of the SLCO1B1 and SLCO1B3 genes, which encode OATP1B1 and OATP1B3, respectively. A number of missense or nonsense mutations of the coding regions (exons) have been found to cause Rotor syndrome. In addition, mutations or insertions within the intronic regions of the genes can cause abnormal splicing or exon inversion [69,70].

Genetic testing can confirm the diagnosis of Rotor syndrome and distinguish it from Dubin-Johnson syndrome. Making a definitive diagnosis of Rotor syndrome is important because of the associated differences in drug metabolism, which may require dose adjustment or elimination of certain drugs. A large number of commonly used drugs are substrates for OATP1B1, OATP1B3, or both (table 1). (See 'Altered drug metabolism' above.)

Genetic testing can be accomplished with next-generation sequencing panels for cholestatic liver diseases. Although whole-exon sequencing can identify a majority of the responsible mutations, whole-genome sequencing is required for identifying intronic mutations or insertions that can cause splicing abnormalities [70]. A list of tests and laboratories is available at the Genetic Testing Registry website.

●Imaging – If oral cholecystography is performed, the gallbladder is usually visualized, in contrast with the finding in Dubin-Johnson syndrome [71].

●Pathology – Liver biopsy is not required for diagnosis. If it is performed, liver histology is normal [71]. The absence of dark melanin-like pigments differentiates this disorder from Dubin-Johnson syndrome. However, distinguishing the two disorders can be done on the basis of urinary coproporphyrin analysis. (See 'Diagnosis' below.)

Diagnosis — Similar to Dubin-Johnson syndrome, Rotor syndrome should be suspected in patients with mild hyperbilirubinemia (with a direct-reacting fraction of approximately 50 percent) in the absence of other abnormalities of standard liver tests, including normal levels of serum alkaline phosphatase and GGTP. These normal laboratory results distinguish these conditions from disorders associated with inherited or acquired diseases associated with liver injury or biliary obstruction.

Differentiation of Rotor syndrome from Dubin-Johnson syndrome — Although both Rotor syndrome and Dubin-Johnson syndrome are generally benign conditions, they need to be distinguished because the two disorders affect the pharmacokinetics of different sets of drugs, thereby increasing their plasma exposure and consequent toxicity. (See 'Management' below.)

To distinguish between these disorders, we start with a urinary coproporphyrin test. If necessary and where available, genetic testing with a next-generation sequencing panel for cholestatic liver disease is an efficient and accurate way to establish the diagnosis of Rotor syndrome and to distinguish it from Dubin-Johnson syndrome (algorithm 1).

●Urinary coproporphyrin excretion – The urinary coproporphyrin excretion pattern can confirm the diagnosis and assist in the distinction between these disorders:

•Normally, approximately 75 percent of urinary porphyrins are coproporphyrin III and the remaining 25 percent are coproporphyrin I.

•In Dubin-Johnson syndrome, the total urinary coproporphyrin excretion is normal, but the ratio is inverted, with 80 percent coproporphyrin I and 20 percent coproporphyrin III. This pattern is unique to Dubin-Johnson syndrome and distinguishes it from Rotor syndrome and from other inherited and acquired cholestatic liver diseases.

•In Rotor syndrome, total urinary coproporphyrins are increased to 250 to 500 percent of normal and approximately 65 percent is coproporphyrin I. However, unlike Dubin-Johnson syndrome, urinary porphyrin analysis does not definitively establish the diagnosis of Rotor syndrome, because this pattern may be found also in some inherited cholestatic disorders and acquired cholestatic liver diseases.

●Genetic testing – If urinary porphyrin analysis is not consistent with Dubin-Johnson syndrome, the diagnosis of Rotor syndrome should be confirmed by genetic testing, which also distinguishes it from Dubin-Johnson syndrome, as well as inherited or acquired cholestatic diseases. (See 'Laboratory tests' above.)

●Other – The plasma clearance of bromsulphthalein (BSP) can also be used to aid in the distinction between these disorders, although this test is no longer used for clinical diagnosis. In Rotor syndrome, BSP clearance is moderately delayed, with increased retention at 45 minutes and no secondary peak. Transport studies for BSP show a 50 percent reduction in transport maximum of this compound, compared with almost no biliary transport in Dubin-Johnson syndrome [72,73]. (See 'Molecular mechanisms' above.)

Liver biopsy is not necessary for the diagnosis of either condition. However, if a biopsy is performed for other clinical indications, the dense pigmentation of the liver seen in Dubin-Johnson syndrome (picture 1) distinguishes it from Rotor syndrome.

Management — As in Dubin-Johnson syndrome, Rotor syndrome does not require treatment. However, it is important to make the diagnosis to avoid confusion with other hepatobiliary diseases. In addition, individuals with Rotor syndrome are at risk for serious drug toxicities, necessitating the avoidance or dose reduction of certain drugs (table 1) [63-66,69,70]. (See 'Altered drug metabolism' above.)

Serum bilirubin levels may increase during pregnancy, requiring differentiation from cholestasis of pregnancy. The latter is usually associated with pruritus, which is not a feature of Dubin-Johnson or Rotor syndromes [11].

Molecular mechanisms — Rotor syndrome is caused by inactivating mutations or deletion of both SLCO1B1 and SLCO1B3, which encode organic anion transporter proteins 1B1 and 1B3 (OATP1B1 and OATP1B3) [62]. OATP1B1 or OATP1B3 also mediate the uptake of many other compounds, including statins and several other drugs. Reduced-activity OATP1B1 resulting from polymorphisms can result in life-threatening drug toxicities, including from statins, methotrexate, and certain other drugs [63]. (See 'Altered drug metabolism' above.)

Normally, bilirubin entering the liver sinusoids is extracted efficiently by hepatocytes that are closest to the points of entry: the portal vein and hepatic artery. Because canalicular excretion is normally rate-limiting in bilirubin throughput, a significant part of the bilirubin is transported back into the sinusoidal blood across the sinusoidal surface of the hepatocytes via the ATP-hydrolysis-dependent pump encoded by ABCC3. Subsequently, the bilirubin undergoes reuptake by hepatocytes downstream to the sinusoidal blood flow via OATP1B1 and OATP1B3. This efflux/reuptake process, called "hepatocyte hopping," results in recruitment of additional hepatocytes downstream to the sinusoidal blood flow, thereby increasing the bilirubin excretory capacity of the liver [62,74]. OATP1B1 and OATP1B3 have distinct but partially overlapping substrates (table 1). Bilirubin glucuronides and bile salts glucuronidated at the 3-carbon position are substrates for both transporters. Therefore, these molecules accumulate in plasma when both OATP1B1 and OATP1B3 are absent or functionally defective [62].

FAMILIAL HEPATOCELLULAR CHOLESTASIS

Progressive familial intrahepatic cholestasis — Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of disorders, characterized by defective secretion of bile acids or other components of bile (table 2). These disorders usually present during infancy or childhood and are associated with growth failure and progressive liver disease.

Related disorders that are associated with heterozygous variants in the same genes include benign recurrent cholestasis (BRIC), low phospholipid-associated cholestasis (LPAC) syndrome, and intrahepatic cholestasis of pregnancy. (See 'Related disorders' below.)

PFIC type 1 (FIC1 deficiency) — PFIC type 1 (PFIC-1; MIM #211600), also known as Byler disease, is caused by biallelic pathogenic variants in ATP8B1, which encodes FIC1 [75,76]. A subtype found in an Inuit population in Greenland and Canada has been called Greenland familial cholestasis [76,77]. FIC1 is located in the canalicular membrane of hepatocytes and in cholangiocytes and is involved with the translocation of acidic phospholipids, which helps maintain the integrity of the cellular membrane in the presence of detergents [78,79]. Additionally, it is critical for the organization of the apical membrane, participating in the membranar localization of proteins such as CDC42, CFTR, and SLC10A2 [80]. FIC1 is also expressed in extrahepatic locations such as the pancreas, small bowel, and cochlear hair cells in the inner ear [81], explaining the extrahepatic manifestations of PFIC-1, such as malabsorption and diarrhea, pancreatitis, neurosensorial hear loss, and increased sweat electrolyte concentration [82].

PFIC-1 usually presents during infancy with cholestatic liver disease, with normal or near-normal serum gamma-glutamyl transpeptidase (GGTP) concentrations. Intractable pruritus is a dominant feature and often presents in early infancy. Affected individuals also may have manifestations of fat-soluble vitamin deficiencies (eg, coagulopathy due to vitamin K malabsorption, rickets due to vitamin D malabsorption). PFIC-1 is probably not associated with an increased risk for hepatocellular carcinoma (HCC), in contrast with PFIC-2 [83].

PFIC type 2 (BSEP deficiency) — PFIC type 2 (PFIC-2; MIM #601847) is caused by biallelic pathogenic variants in ABCB11 which encodes the bile salt export pump (BSEP) (figure 1). BSEP is an ATP-dependent transporter of bile acids from the hepatocytes into the bile canaliculus [1]. Over 80 different mutations in ABCB11 have been described in patients with PFIC-2 [84]. Monoallelic mutations of ABCB11 are associated with a more benign and recurrent course often first presenting in adulthood. (See 'Related disorders' below.)

PFIC-2 resembles PFIC-1 clinically but occurs in other families, mainly in the Middle East and Europe. Both disorders are associated with severe cholestasis and pruritus, with normal or near-normal GGTP [85]. The course of PFIC-2 is variable and partly predicted by the genotype. As examples, individuals with homozygous p.D482G or p.E297G variants tend to have a milder course, with a better response to surgical/medical interruption of the enterohepatic circulation, and may not require liver transplantation. By contrast, individuals with a protein-truncating mutation usually have rapidly progressive disease that often requires liver transplantation at an early age, as well as a high risk for HCC [86,87]. Indeed, HCC, which is rare in young children, is a frequent event, developing very early, with 70 percent of the cases occurring before the age of two years [86]. Thus, ABCB11 mutations represent a previously unrecognized risk for HCC in young children [86].

PFIC type 3 (MDR3 deficiency) — Biallelic pathogenic variants in the ABCB4 gene, which encodes multidrug resistance protein-3 P-glycoprotein (MDR3) (figure 1), cause PFIC type 3 (PFIC-3; MIM #602347) [88]. The disorder is characterized by markedly elevated serum GGTP activity, which distinguishes it from PFIC-1, PFIC-2, and BRIC [85]. Risks for complicated biliary stones, intrahepatic cholestasis of pregnancy, HCC, and cholangiocarcinoma has been reported [87,89,90].

MDR3 replenishes the phosphatidylcholine in the outer lipid membrane of the bile canaliculus by translocating ("flopping") it from the inner lipid layer [91]. In the absence of phosphatidylcholine translocation, bile acids are thought to damage the canalicular membrane, causing progressive destruction of small bile ducts [92,93]. However, bile salt secretion remains normal.

Other forms of PFIC

●TJP2 variants – Homozygous variants in TJP2 cause PFIC type 4 (PFIC-4; MIM #615878). This disorder is characterized by severe chronic cholestatic liver disease, with low serum GGTP levels for the degree of cholestasis (similar to PFIC-1 and 2). Truncation of the TJP2 protein results in failure of its incorporation into tight junctions delimiting the bile canaliculi. This causes the failure of claudin1 (CLDN1) to localize in the cholangiocyte-cholangiocyte borders and margins of bile canaliculi. Interestingly, the pathology appears to be limited to the liver. This disorder was described in two case series comprising 77 affected children [94,95]. As in many other rare monogenic disorders, there was a high incidence of consanguinity, which was present in a majority of families. HCC has been described in approximately 10 percent of people with PFIC-4 [83,96].

●ZFYVE19 variants – Biallelic pathgenic variants in ZFYVE19 cause PFIC type 9 (PFIC-9; MIM #619849). This neonatal-onset chronic cholestatic disease is characterized by hepatosplenomegaly; pruritus; and elevation of serum GGTP, alanine aminotransferase (ALT), and aspartate aminotransferase (AST), with retained hepatic protein synthetic function [97-100]. Liver histology reveals features seen in congenital hepatic fibrosis, and the condition often progresses to micronodular cirrhosis. Limited data from case reports suggest that pharmacologic treatment (ursodeoxycholic acid [UDCA], odevixibat) can be effective [97,99], but the natural history and prognosis are not well understood.

ZFYVE19 encodes ANCHR, which is important in protein sorting to appropriate cellular sites, including polarized trafficking of BSEP to hepatocyte canalicular membrane [101]. The interference with BSEP trafficking partly explains the phenotype. However, in contrast with PFIC-2, serum GGTP levels are consistely elevated, suggesting the presence of additional pathogenetic mechanisms. Interestingly, during interphase and early mitosis, ANCHR is located mainly in centrosomes, which stabilize the primary cilium of bile duct epithelial cells. Destabilization of these primary cilia has been proposed as an additional mechanism of high-GGT cholestasis and hepatic fibrosis [101].

●Other – Other forms of PFIC can be caused by pathogenic variants in NR1H4, SLC51A, USP53, KIF12, MYO5B, SEMA7A, and VPS33B [79].

Medical management — The general approach to treatment is similar for all types of PFIC, but response to treatment varies substantially, in part depending on genotype.

●General measures – Medical treatment, combined with nutrition support (high-calorie, medium-chain triglycerides and high-protein diet) and supplementation with fat-soluble vitamins, is typically the first-line approach in patients with all types of PFIC to prevent sequelae and complications of chronic cholestasis.

The most widely used initial medical therapy for all patients with PFIC is UDCA, which changes the bile acid composition, reducing the amount of toxic bile acids, increasing bile production, and also possibly having an immunomodulatory effect [102]. Together, these actions may improve cholestatic pruritus, decrease cholestasis, reduce bile acid toxicity, and reduce and prevent cholelithiasis. The efficacy of UDCA is generally low in PFIC-1 (FIC1 deficiency) and PFIC-2 (BSEP deficiency) and not sustained. The efficacy is variable in PFIC-3 (MDR3 deficiency), ranging from none to high, related to genotype. UDCA is not effective in individuals with truncated mutations, because it requires some residual MDR3 activity [79,102]. Nonetheless, a trial of UCDA is widely prescribed in patients with all types of PFIC, given its favorable side effect profile. UDCA dosing is provider dependent but generally similar to its off-label use in other cholestatic liver diseases. Our typical practice to dose at 20 mg/kg/day divided twice daily (maximum 300 mg twice daily) [103,104], but, for children, we may increase up to 25 to 30 mg/kg/day (maximum 300 mg twice daily) as needed. UDCA is well tolerated and associated with few adverse effects [105]. The most common adverse effect is diarrhea, which generally improves with lowering the dose.

Patients with cholelithiasis may require endoscopic or surgical removal of gallstones. Treatment with UDCA also may help prevent gallstone formation by replacing endogenous lithogenic bile acids with a hydrophylic bile acid [106,107].

●Pruritus – Pruritus is often the predominant symptom in many patients with PFIC. Although the mechanism of pruritus of cholestasis is not fully understood, several classes of pruritogens have been recognized: bile acids; the enzyme autotaxin, which cleaves lysophosphatidylcholine, forming lysophosphatidic acid [108]; endogenous opioids; the neurotransmitter serotonin; and unidentified pruritogens.

We use a sequential approach for the medical treatment of pruritus [109]:

•UDCA – Initial therapy for pruritus is UDCA, as described above.

•Ilial bile acid transport (IBAT) inhibitors – An alternative approach to reduce serum bile acid levels consists of pharmacologic inhibition of ileal sodium/bile acid transport by the nonabsorbable small-molecule drugs odevixibat [110] or maralixibat [111], which are reversible IBAT inhibitors. Both drugs have been approved for the treatment of pruritus in patients with PFIC (odevixibat for age ≥3 months, maralixibat for age ≥12 months). They are not recommended for the subgroup of patients with PFIC-2 who have a protein-truncating variant of ABCB11. This genotype leads to a severe bile acid/salt transport defect, so that bile acid secretion into the bile is negligible. In a phase 3 clinical trial of 93 children with PFIC (excluding those with ABCB11 protein-truncating variants), maralixibat significantly improved pruritus scores and reduced serum bile acids compared with placebo [112]. Generally similar results were seen in a trial of odevixibat in children with PFIC [113]. Furthermore, preliminary data suggested that odevixibat was associated with a benefit in event-free survival, as compared with untreated control patients from a registry [114].

Adverse effects of IBAT inhibitors include diarrhea due to the effect of the unabsorbed bile acids on the colonic epithelium. Bile acid depletion can result in the deficiency of fat-soluble vitamins (A, D, E, and K), causing coagulation disorders and bone fracture. Therefore, baseline serum levels of these vitamins should be established before starting treatment and followed up intermittently to determine the need for supplementation and possible treatment interruption. These drugs also can cause hepatotoxicity. Therefore, serum ALT, AST, GGTP, bilirubin levels, and prothrombin time (international normalized ratio) should be determined before initiation of treatment and every six to eight months during the course of the treatment for potential dose adjustment or discontinuation of these drugs.

Both of these drugs are started at lower doses, then gradually increased as tolerated, as outlined in the UpToDate LexiDrug prescribing information (odevixibat and maralixibat). Note that dosing is different for PFIC compared with Alagille syndrome. If cholestyramine is used in addition to either odevixibat or maralixibat, it should be administered at least four hours apart from these drugs.

•Rifampin – The second line of therapy aims at increasing the metabolism and excretion of pruritogens using rifampin, a pregnane X-receptor agonist and a potent inducer of key enzymes in hepatic and intestinal detoxification, and the export pump MRP2 [115]. Rifampin reduces serum autotaxin levels. Because of an approximately 5 percent incidence of drug-induced liver injury in children, rifampin should be initiated at a low dose (150 mg/day for adults), with serial monitoring of serologic liver tests and blood count, before escalating the dose to maximum of 600 mg/day [115]. For children, a starting dose is 4 mg/kg/day orally, divided in two doses, escalating if needed to 10 to 20 mg/kg/day (maximum 600 mg/day).

•Naltrexone – If rifampin therapy fails to reduce itching, the third line of therapy should be naltrexone, the oral opioid antagonist [116]. Naltrexone should be started at a low dose and increased by one-quarter every three to seven days to avoid the self-limited withdrawal-like syndrome in the first days of treatment caused by dissociation of endogenous opioids from their receptors [117]. For adults, the starting dose is 12.5 mg, escalating to 50 mg/day. For children, the dose is 0.25 to 0.5 mg/kg orally once daily (maximum 50 mg/dose). To prevent a "breakthrough" phenomenon during long-term therapy, naltrexone may be withheld two days a week.

•Sertraline – Finally, the selective serotonin reuptake inhibitor sertraline, which increases neurotransmitter concentrations within the central nervous system [118], may be considered as a fourth-line treatment for patients resistant to the above mentioned treatments. Sertraline is started at 25 mg/day in adults, increasing gradually to 75 to 100 mg/day, and can be also used in addition to rifampicin therapy. For children, doses are 1 to 4 mg/kg/day orally (maximum 100 mg/day).

•4-phenylbutyrate – For some children with PFIC-1 (FIC1 deficiency) or PFIC-2 (BSEP deficiency), preliminary evidence from case reports suggests that 4-phenylbutyrate may be helpful. For the subset of patients with PFIC-2 that is caused by ABCB11 missense mutations, 4-phenylbutyrate improves BSEP trafficking to the canalicular membrane, based on experiments in transfected cell lines [119,120]. In a study of four patients with this type of mutation, treatment with 4-phenylbutyrate resulted in improvements in pruritus, serum bile acid concentration, and serum liver tests [121]. In addition, canalicular localization of BSEP was demonstrated by immunostaining of liver biopsies obtained in three of the patients after 4-phenylbutyrate therapy. In a case series of three children with PFIC-1, 4-phenylbutyrate improved pruritus but not biochemical indices of cholestasis [122,123]. In this type of PFIC, 4-phenylbutyrate appears to increase BSEP expression rather than trafficking.

•Cholestyramine – In the past, cholestyramine was sometimes used if pruritus was not relieved by UDCA. The goal was to deplete the bile acid pool by binding it in the intestine. However, this approach has low efficacy in children with PFIC, in which biliary excetion of bile is very low [124]. Moreover, use of cholestyramine in children is limited by nausea, constipation, and diarrhea, as well as decreased absortion of other drugs when administered less than four hours apart.

Surgical management — Despite medical management, many individuals with PFIC have intractable pruritus and/or progressive liver disease that ultimately require surgical management:

●Bile diversion – In some patients, pruritus may be refractory to pharmacologic intervention. In these patients, surgical procedures to interrupt the enterohepatic circulation of bile acids are often successful. This can be done by diverting part of the bile flow to an external fistula, where it is discarded [125-127]. Biochemical improvements are often seen, suggesting that the diversion procedure might slow the progression of liver disease [127-129].

●Liver transplantation – Liver transplantation is an important option for patients with end-stage liver disease due to PFIC and for some patients with pruritus that is unresponsive to the measures described above [130]. In various series, between 20 and 80 percent of individuals with PFIC ultimately progressed to liver transplantation [131].

Liver transplantation is generally curative for patients with PFIC (graft survival approximately 75 percent, patient survival 85 percent [132]), with the following caveats:

•Patients with PFIC-1 may have ongoing disease after liver transplant due to the extrahepatic expression of FIC1 [133,134]. In a case report, post-liver transplantation steatohepatitis in a two-year-old patient with PFIC-1 was ameliorated after performing a total internal biliary diversion [135]. Transplantation also may be complicated by intractable chronic diarrhea, related to bile salt malabsorption [136,137].

•For patients with PFIC-2, liver transplantation generally resolves all disease manifestations. However, in approximately 8 percent of children with PFIC-2, the disease recurs after liver transplantation, probably as a consequence of the development of high titer antibodies against BSEP and deposition of these antibodies, as well as the complement component protein C4d in liver sinusoids [138-142]. Recurrent BSEP disease may be ameliorated by antibody-depletion therapies, such as a monoclonal antibody against the CD20 antigen of B cells (eg, rituximab) with or without plasmapheresis [141], but a second liver transplantation may be needed, which is associated with a high mortality rate. Antibody-induced BSEP deficiency has been reported to be reversed by allogeneic bone marrow transplantation in a patient with PFIC-2 who had received liver transplantation [142].

•For patients with PFIC-3, liver transplantation is also curative, with resolution of hepatic and extrahepatic symptoms. Patient and graft survival appear to be excellent, based on small case series [132,143-146].

Related disorders — Several phenotypes are associated with monoallelic pathogenic variants in the same genes that cause PFIC, as outlined below. These disorders are often triggered by environmental factors, including drugs or intercurrent illnesses. Affected individuals also have increased risk for intrahepatic cholestasis of pregnancy. (See "Intrahepatic cholestasis of pregnancy".)

Benign recurrent intrahepatic cholestasis

●Clinical manifestations – BRIC is characterized by intermittent cholestatic episodes [147]. Age at first presentation ranges from infancy to late adulthood. The number of attacks can range from several episodes per year to one episode in a decade [148-151]. During the attacks, the patient presents with conjugated hyperbilirubinemia, malaise, anorexia, pruritus, weight loss, and malabsorption. Laboratory tests reveal biochemical evidence of cholestasis without severe hepatocellular injury [149,152,153]. Such episodes last for weeks to months, followed by a complete clinical, biochemical, and histologic normalization. In a given patient, recurrent attacks resemble each other in symptoms, signs, and duration, although the severity and frequency of the episodes appear to decrease with age.

BRIC has long been thought to be associated with intrahepatic cholestasis of pregnancy and cholestasis associated with use of oral contraceptives. In one study, 11 members of kindred of whom three members had been affected by BRIC developed intrahepatic cholestasis of pregnancy, cholestasis associated with oral contraceptives, or both [148].

Liver histology reveals noninflammatory intrahepatic cholestasis without fibrosis, regardless of the number and severity of attacks. During remission, liver histology returns to normal whether examined by light or electron microscopy [154].

●Molecular pathogenesis – Family studies suggest a recessive inheritance pattern. Surprisingly, this relatively benign disorder was also found to be associated with mutations of the ATP8B1 (FIC1) and ABCB11 (BSEP) genes, which are associated with PFIC-1 and PFIC-2, respectively [155]. As an example, a patient with clinical features of BRIC was found to have two different mutations on the two alleles of the ABCB11: a E186G substitution (previously described in a BRIC-2 case) and a V444A substitution (linked to intrahepatic cholestasis of pregnancy). The compound heterozygosity led to the absence of BSEP in bile canaliculi of hepatocytes. Bile salt excretion was reduced [156].

It has been proposed that BRIC caused by mutations of ATP8B1 and ABCB11 should be termed BRIC-1 and BRIC-2, respectively [155]. There are clinical differences between these two subtypes, suggesting that it may be appropriate to subclassify BRIC into at least two distinct disorders (BRIC type 1 and 2). Pancreatitis is a known extrahepatic manifestation in BRIC caused by the ATPB1 mutations but not in BRIC patients with mutations in ABCB11. Similarly, cholelithiasis has been described in patients with the ABCB11 mutation but not in those with the ATP8B1 mutation [157].

●Treatment – There is no specific treatment for BRIC. Liver transplantation is generally not considered, because of the episodic and nonprogressive nature of the disease, although the pruritus can be severe enough for the patient to seek liver transplantation. Short-term nasobiliary drainage has been reported to improve pruritus in a patient with BRIC, presumably by normalizing serum bile salt concentrations [158]. Rapid termination of cholestatic episode was reported in a 34-year-old man with BRIC and secondary kidney function impairment, following extracorporeal albumin dialysis in a molecular adsorbent recirculating system (MARS) [159]. Administration of colestimide, an anion exchange resin that inhibits intestinal bile acid absorption, resulted in rapid remission of the cholestatic episode in one patient [160].

Low phospholipid associated cholestasis syndrome — LPAC syndrome is characterized by cholelithiasis before age 40, recurrence after cholecystectomy, and intrahepatic hyperechogenic foci compatible with sludge or microlithiasis [161]. Many patients have a family history of cholelithiasis in first-degree relatives or a clinical history of intrahepatic cholestasis of pregnancy [106]. Affected individuals are at increased risk for hepatobiliary malignancy [79]. (See "Intrahepatic cholestasis of pregnancy".)

LPAC syndrome is caused by heterozygous variants in ABCB4 (rather than the biallelic variants that cause PFIC-3). These variants can reduce biliary phospholipid concentration, resulting in increased risk for cholesterol stones, microlithiasis, or sludge. Approximately one-third of adult patients presenting with unexplained cholestasis have mutations in the coding region of at least one ABCB4 allele [107]. ABCB4 variants are also associated with acute recurrent biliary pancreatitis, biliary cirrhosis, and fibrosing cholestatic liver disease in adults, with or without biliary symptoms [107,162].

These patients should be treated with UDCA at a dose of 13 to 15 mg/kg/day and annual surveillance with laboratory tests, noninvasive markers of liver fibrosis, and ultrasound (to screen for liver malignancy) [79].

BILE CANALICULAR AND STRUCTURAL ANOMALIES OF KNOWN GENETIC BASIS — 

The genetic basis of two disorders involving bile canalicular and structural anomalies has been described: Alagille syndrome and abnormalities of villin gene expression.

Alagille syndrome — Alagille syndrome is characterized by the paucity of interlobular bile ducts and chronic cholestasis, often with severe liver disease [163-166]. Most patients have associated anomalies including cardiac anomalies (eg, peripheral pulmonic stenosis), butterfly vertebrae, posterior embryotoxon, dysmorphic facies, and sometimes poor growth, developmental delay, kidney disease, and pancreatic insufficiency. The syndrome is inherited as an autosomal dominant characteristic. It is usually caused by pathogenic variants in the JAG1 gene or, occasionaly, by NOTCH2 variants.

The clinical manifestations, diagnosis, and management of Alagille syndrome are discussed in detail separately. (See "Alagille syndrome".)

Abnormal villin expression — This inherited disease is characterized by a biliary atresia-like presentation with special ultrastructural features. In a review of 50 children who underwent orthotopic liver transplantation for a clinical diagnosis of biliary atresia, three were found to have aberrant ultrastructural findings and a lack of villin expression in the bile canaliculi, as determined by immunohistochemical staining [167]. Each of these patients had clinical features of cholestasis including elevations in serum alkaline phosphatase (356 to 788 international units), gamma-glutamyl transpeptidase (GGTP; 76 to 203 U/L), and bilirubin (16 to 26 mg/dL). All patients had cirrhosis at the time of liver transplantation at the age of two to five years. Histologic examination of the liver showed paucity or absence of bile ducts and only a moderate degree of portal fibrosis at the age of three months, which distinguished these cases from classic biliary atresia. Electron microscopy revealed disordered canalicular microvilli, which were often inverted (ie, projected into the cytoplasm rather than the canalicular lumen).

Absence of villin gene expression is thought to be the mechanism causing this disorder. Villin is a protein involved in binding actin and arranging actin fibers in bundles, which are necessary for generating and maintaining anatomically normal microvilli. The human villin gene has been mapped to chromosome 2q35-36 [168]. The protein is expressed in the microvilli of brush-border surfaces in the gastrointestinal tract and kidney [169]. Interestingly, patients with abnormal villin gene expression do not exhibit clinical features of malabsorption, pancreatic abnormality, or kidney disease.

Villin gene knockout mice show an abnormal response to intracellular calcium and develop colonic ulcers when fed with dextran sulfate [170]. However, in contrast with the human cases, no obvious liver phenotype was found. The mechanistic basis of these discrepancies is unknown.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Genetic liver diseases".)

SUMMARY AND RECOMMENDATIONS

●Classification – Elimination of conjugated bilirubin in bile is affected in several inherited disorders that work through different mechanisms. In all of these situations, the abnormality of biliary excretion of bilirubin is shared with excretory defect of all or some other organic anions, bile salts, or phospholipids (figure 1). (See 'Classification' above.)

●Dubin-Johnson syndrome – Dubin-Johnson syndrome is a generally benign condition characterized by mild icterus and fluctuating conjugated hyperbilirubinemia that may be exacerbated by intercurrent illnesses, pregnancy, or consumption of oral contraceptives. Otherwise, patients are asymptomatic. It is caused by defective canalicular excretion of conjugated bilirubin and many other organic anions. The liver is black. No treatment is required. However, it is important to recognize the condition to distinguish it from Rotor syndrome and other hepatobiliary disorders characterized by conjugated hyperbilirubinemia (algorithm 1). Also, pharmacokinetics of a number of drugs may be altered in Dubin-Johnson syndrome, requiring dose adjustment. (See 'Dubin-Johnson syndrome' above.)

●Rotor syndrome – Rotor syndrome is another rare, generally benign condition characterized by mild icterus and fluctuating conjugated and unconjugated hyperbilirubinemia without evidence of hemolysis. The defect is in the reuptake of the fraction of conjugated bilirubin, which is secreted into the sinusoidal blood by hepatocytes. Similar to Dubin-Johnson syndrome, no treatment is required, but diagnosing the condition is important to avoid confusion with other hepatobiliary disorders characterized by conjugated hyperbilirubinemia. In addition, affected individuals are at risk for serious drug toxicities, including from statins, methotrexate, and many other drugs (table 1). (See 'Rotor syndrome' above.)

●Familial hepatocellular cholestasis – Familial hepatocellular cholestasis includes progressive familial intrahepatic cholestasis (PFIC), which is characterized by severe cholestatic liver disease and pruritus and is subclassified into several types (table 2). For most patients with PFIC, we suggest a trial of ursodeoxycholic acid (UDCA) (Grade 2C). Although UDCA has variable efficacy for pruritus and biomarkers of cholestasis, the drug has a favorable side effect profile. Options for addon therapy for pruritus includes antihistamines, rifampin, and ileal bile acid transport (IBAT) inhibitors (maralixibat or odevixibat). Other interventions include bile acid diversion for patients with refractory pruritus or liver transplantation for those with end-stage liver disease. (See 'Progressive familial intrahepatic cholestasis' above and 'Medical management' above.)

●Related disorders – Monoallelic pathogenic variants in the genes that cause PFIC are associated with milder cholestatic phenotypes, including benign recurrent intrahepatic cholestasis (BRIC), low phospholipid associated cholestasis (LPAC) syndrome, and some forms of intrahepatic cholestasis of pregnancy. (See 'Familial hepatocellular cholestasis' above and "Intrahepatic cholestasis of pregnancy".)

●Other – Genetic disorders characterized by bile canalicular and structural anomalies include Alagille syndrome and abnormal villin expression. (See "Alagille syndrome" and 'Bile canalicular and structural anomalies of known genetic basis' above.)