Benign recurrent intrahepatic cholestasis (BRIC): evidence of genetic heterogeneity and delimitation of the BRIC locus to a 7-cM interval between D18S69 and D18S64

The ascending pathophysiology of cholestatic liver disease

In this review we develop the argument that cholestatic liver diseases, particularly primary biliary cholangitis and primary sclerosing cholangitis (PSC), evolve over time with anatomically an ascending course of the disease process. The first and early lesions are in "downstream" bile ducts. This eventually leads to cholestasis, and this causes bile salt (BS)-mediated toxic injury of the "upstream" liver parenchyma. BS are toxic in high concentration. These concentrations are present in the canalicular network, bile ducts, and gallbladder. Leakage of bile from this network and ducts could be an important driver of toxicity. The liver has a great capacity to adapt to cholestasis, and this may contribute to a variable symptom-poor interval that is often observed. Current trials with drugs that target BS toxicity are effective in only about 50%-60% of primary biliary cholangitis patients, with no effective therapy in PSC. This motivated us to develop and propose a new view on the pathophysiology of primary biliary cholangitis and PSC in the hope that these new drugs can be used more effectively. These views may lead to better stratification of these diseases and to recommendations on a more "tailored" use of the new therapeutic agents that are currently tested in clinical trials. Apical sodium-dependent BS transporter inhibitors that reduce intestinal BS absorption lower the BS load and are best used in cholestatic patients. The effectiveness of BS synthesis-suppressing drugs, such as farnesoid X receptor agonists, is greatest when optimal adaptation is not yet established. By the time cytochrome P450 7A1 expression is reduced these drugs may be less effective. Anti-inflammatory agents are probably most effective in early disease, while drugs that antagonize BS toxicity, such as ursodeoxycholic acid and nor-ursodeoxycholic acid, may be effective at all disease stages. Endoscopic stenting in PSC should be reserved for situations of intercurrent cholestasis and cholangitis, not for cholestasis in end-stage disease. These are arguments to consider a step-wise pathophysiology for these diseases, with therapy adjusted to disease stage. An obstacle in such an approach is that disease stage-defining biomarkers are still lacking. This review is meant to serve as a call to prioritize the development of biomarkers that help to obtain a better stratification of these diseases. (Hepatology 2017;65:722-738).

Progressive familial intrahepatic cholestasis: genetic disorders of biliary transporters

Progressive familial intrahepatic cholestasis types 1, 2 and 3 are childhood diseases of the liver. Benign recurrent intrahepatic cholestasis is predominantly an adult form with similar clinical symptoms that spontaneously resolve. These genetic disorders have significantly helped to unravel the basic mechanisms of the canalicular bile transport processes. Progressive familial intrahepatic cholestasis type 1 involves a gene also linked to benign recurrent intrahepatic cholestasis. The gene codes for an aminophospholipid translocase protein that maintains the integrity of the membrane. How a mutation in this protein causes cholestasis is unknown but is thought to involve the enterohepatic recirculation of bile acids. Progressive familial intrahepatic cholestasis types 2 and 3 involve the canalicular bile salt export pump and a phospholipid translocase, respectively, both of which are fundamental to bile secretion. This review covers the clinical manifestations, genetics, treatment and mechanism of each disease.

Benign recurrent intrahepatic cholestasis

Benign recurrent intrahepatic cholestasis is a rare autosomal recessive disorder characterized by repeated episodes of intense pruritus, profound elevations in serum alkaline phosphatase and bilirubin, with normal or nearly normal values for serum gamma-glutamyl transferase. Attack lasts from several weeks to months and resolve spontaneously. Between attacks patients remain asymptomatic for months to years. The disorder does not lead to progressive liver injury and is not fatal. Genetic studies have demonstrated that the disorder is the result of a mutation in ATP8BI, a gene that codes for the FIC1 (familial intrahepatic cholestasis) protein, which is also affected in other forms of familial intrahepatic cholestasis. It is believed this protein plays a role in bile acid secretion, in aminophospholid transport, and in maintaining fluidity of the cell membrane. Therapy is supportive and aimed at relieving pruritus and other complications of severe cholestasis until the episode resolves spontaneously.

Hereditary forms of intrahepatic cholestasis

Several genes that are mutated in hereditary forms of intrahepatic cholestasis have been identified or mapped, providing new insights into the process of enterohepatic bile acid circulation in health and disease and new tools with which to study this process. Murine models of several of these disorders have been generated. Unanticipated genetic heterogeneity has been identified.

Benign recurrent intrahepatic cholestasis progressing to progressive familial intrahepatic cholestasis: low GGT cholestasis is a clinical continuum

Benign recurrent intrahepatic cholestasis (BRIC) is an autosomal recessive liver disease, characterised by intermittent attacks of cholestasis, which can start at any age and last for several weeks to months. Characteristically serum GGT activity is low and normal liver structure is preserved. Progressive familial intrahepatic cholestasis (PFIC) is another liver disease, characterised by severe cholestasis, starting almost invariably before 6 months of age. All patients progress to cirrhosis, liver failure and death, unless a liver transplantation is performed. We now identified four patients who presented in childhood with recurrent attacks of cholestasis, while in the course of the disease the cholestasis gradually became permanent. Although liver biopsies performed in the early stages of the disease showed normal liver architecture, late stage biopsies revealed evident fibrosis with porto-portal septa formation. In conclusion, the disease of these patients started with the clinical and histopathological characteristics of BRIC but progressed to PFIC.

A case of severe benign intrahepatic cholestasis treated with liver transplantation

A male patient with benign recurrent cholestasis since age 2.5 yr developed unremitting cholestasis with incapacitating pruritus and hepatic fibrosis by age 21. He was tried on numerous medical therapies for pruritus with transient or no relief. He responded only temporarily to biweekly plasmapheresis, which was carried out for 4 yr. He underwent orthotopic liver transplantation at age 25 with immediate resolution of his pruritus. At age 30 he is a happy, asymptomatic, fully employed professional.

Autosomal dominant benign recurrent intrahepatic cholestasis (BRIC) unlinked to 18q21 and 2q24

Benign recurrent intrahepatic cholestasis (BRIC) is an autosomal recessive liver disease characterized by multiple episodes of cholestasis without progression to chronic liver disease. On the basis of recent evidence of locus heterogeneity, we studied 19 subjects (7 affected members) of a BRIC family. Male-to-male transmission and the presence of affected females suggested autosomal dominant inheritance. Blood samples were collected after informed consent. Subjects were genotyped by using markers mapping to 18q and 2q24 region, respectively, where the genes FIC1 and FIC2 have been mapped. Segregation of haplotypes excluded the two regions in our family. These findings suggest further genetic heterogeneity of the origin of BRIC.

A missense mutation in FIC1 is associated with greenland familial cholestasis

Greenland familial cholestasis is a severe form of intrahepatic cholestasis described among indigenous Inuit families in Greenland. Patients present with jaundice, pruritus, bleeding episodes, and steatorrhea, and die in childhood due to end-stage liver disease. We investigated the possibility that Greenland familial cholestasis is caused by a mutation in FIC1, the gene defective in patients with progressive familial intrahepatic cholestasis type 1 and many cases of benign recurrent intrahepatic cholestasis. Using single-strand conformation polymorphism analysis and sequencing of the FIC1 exons, a missense mutation, 1660 G-->A (D554N), was detected and was shown to segregate with the disease in Inuit patients from Greenland and Canada. Examination of liver specimens from 3 Inuit patients homozygous for this mutation revealed bland canalicular cholestasis and, on transmission electron microscopy, coarsely granular Byler bile, as previously described in patients with progressive familial intrahepatic cholestasis type 1. These data establish Greenland familial cholestasis as a form of progressive familial intrahepatic cholestasis type 1 and further underscore the importance of unimpeded FIC1 activity for normal bile formation.

The pathophysiology of cholestasis with special reference to primary biliary cirrhosis

Cholestasis in primary biliary cirrhosis results from impairment of bile flow either by reduced transport at the level of the canaliculi or by disturbed bile flow through damaged intrahepatic bile ductules. Whatever its cause, the expression of hepatic transport proteins will be affected. In cholestatic rats: the expression of the multispecific organic anion transporter mrp2 is decreased; the bile salt export pump bsep and the phospholipid transporter mdr2 are less affected; the carrier protein for hepatic uptake of bile salts ntcp is sharply down-regulated; Mrp3, a basolateral ATP-dependent transporter for glucuronides and bile salts, is upregulated. Thus, bile salts that cannot exit the hepatocyte because of the cholestasis are effectively removed across the basolateral membrane. These may be adaptive responses in defence against overloading of hepatocytes with cytotoxic bile salts. These responses show that the expression of hepatic transporter proteins is highly regulated. This occurs by transcriptional and post-transcriptional mechanisms. Primary biliary cirrhosis starts as a disease of the small intrahepatic bile ducts and therefore the experimental evidence for 'cross-talk' between hepatocytes and cholangiocytes is of great interest for this disease and needs to be further investigated. New insights in bile physiology may enable the development of new therapies for cholestatic liver diseases as primary biliary cirrhosis.

Advances in familial and congenital cholestatic diseases. Clinical and diagnostic implications

Recent progress in liver cell biology and molecular genetics revealed that a number of familial and congenital cholestatic disorders are caused by mutations in genes coding for hepatobiliary-transporter or for signalling proteins involved in morphogenesis. The status of the field is reviewed in the light of its impact on current diagnostic and clinical practice. The heterogeneous progressive familial intrahepatic cholestasis can now be separated into different genetic diseases. FIC1-defective progressive familial intrahepatic cholestasis (previously Byler disease) is determined by mutations in the FIC1 gene, coding for P-type ATPases of unknown physiological function, while a second form (bile salt export pump defective progressive familial intrahepatic cholestatis) is caused by a defective function of the canalicular bile salt export pump. Furthermore, a group of progressive familial intrahepatic cholestasis patients with high serum gamma glutamyltranspeptidase have mutations in the gene (PGY3) coding for the MDR3 protein, a canalicular ATP-dependent phopshatidylcholine translocator. Recurrent intrahepatic cholestasis (previously benign recurrent cholestasis), is also linked to specific mutations in the FIC1 gene. Finally, in Alagille syndrome, mutations in the JAG1 gene cause deficiency Jagged 1, a ligand for Notch 1, a receptor determining cell fate during early embryogenesis. Diagnosis of Alagille syndrome, a condition that should be suspected in all patients with unexplained cholestasis, will thus be confirmed by genetic analysis for mutations of JAG1. In children with cholestasis and low serum bile acid levels, an inborn error of bile acid synthesis should be excluded by urinary bile acid analysis by means of fast atom bombardment-ionization mass-spectrometry. In contrast, in children with cholestasis and high serum bile acid concentrations, a high serum gamma glutamyltranspeptidase value would indicate MDR3 deficiency, which should be excluded through biliary phospholipid determination and genetic analysis of PGY3 gene. Finally, in those children with cholestasis, high serum bile acids and low gamma glutamyltranspeptidase activity, analysis of mutation in FIC1 and bile salt export pump genes may lead to the diagnosis of progressive familial intrahepatic cholestasis either from bile salt export pump or FIC1 deficiency.

Hepatocanalicular bile salt export pump deficiency in patients with progressive familial intrahepatic cholestasis

BACKGROUND & AIMS

Progressive familial intrahepatic cholestasis (PFIC), an inherited liver disease of childhood, is characterized by cholestasis and either normal or increased serum gamma-glutamyltransferase activity. Patients with normal gamma-glutamyltransferase activity have mutations of the FIC1 locus on chromosome 18q21 or mutations of the BSEP gene on chromosome 2q24. Also, patients with bile acid synthesis defects have low gamma-glutamyltransferase activity. We investigated expression of the bile salt export pump (BSEP) in liver samples from patients with a PFIC phenotype and correlated this with BSEP gene mutations.

METHODS

BSEP and multidrug resistance protein 2 (MRP2) expressions were studied by immunohistochemistry in liver specimens of 28 patients and BSEP gene mutation analysis in 19 patients. Bile salt kinetics were studied in 1 patient.

RESULTS

Sixteen of 28 liver samples showed no canalicular BSEP staining. Staining for MRP2 showed a normal canalicular pattern in all but 1 of these samples. Ten of 19 patients showed BSEP gene mutations; BSEP protein expression was lacking in all 10 patients. No mutations were found in 9 of 19 patients, and in all except 1, BSEP protein expression was normal. Bile salt concentration in bile of BSEP-negative/MRP2-positive PFIC patients was 0.2 +/- 0.2 mmol/L (n = 9; <1% of normal) and in BSEP-positive PFIC patients 18.1 +/- 9.9 mmol/L (n = 3; 40% of normal). The kinetic study confirmed the dramatic decrease of bile salt secretion in BSEP-negative patients.

CONCLUSIONS

The findings show a close correlation between BSEP gene mutations and canalicular BSEP expression. Biliary secretion of bile salts is greatly reduced in BSEP-negative patients.

Benign recurrent intrahepatic cholestasis

Benign recurrent intrahepatic cholestasis is a rare autosomal recessive disorder characterized by repeated episodes of intense pruritus and jaundice. Each attack lasts from several weeks to months before resolving spontaneously. Patients are completely asymptomatic for months to years between symptomatic periods. The disorder does not lead to progressive liver disease. Although attacks seem to be associated with a viral prodrome, an inciting viral agent or toxin has not been defined. Genetic studies have mapped the defect of this disorder to the long arm of chromosome 18 and a gene that codes for a P-type ATPase, which appears to be involved in aminophospholipid transport. Therapy during symptomatic periods is supportive and aimed at relief of severe pruritus until the episode resolves spontaneously.

Recurrent familial intrahepatic cholestasis in the Faeroe Islands. Phenotypic heterogeneity but genetic homogeneity

Recurrent familial intrahepatic cholestasis is an autosomal recessive disorder characterized by episodes of severe pruritus and jaundice lasting for weeks to months without extrahepatic bile duct obstruction. Symptom-free intervals may last for months to years, and chronic liver damage does not develop. We recently studied four of the five patients from the Faeroe Islands described by us 30 years ago (one had recently died) and an additional five patients that were identified after the initial report. The episodes of cholestasis were more frequent and severe in patients with early onset, but tended to reduce in frequency with age. The youngest patient, aged 25 years, who had had 16 episodes each lasting about 6 months, had a liver transplant after which no further episodes were recorded (1 year after surgery). Signs of chronic liver disease were absent in all patients. The FIC1 gene was investigated for mutations in the surviving patients. A single mutation (I661T) was found on both chromosomes in all nine patients, indicating that they are genetically identical for the disease-causing defect. Nevertheless, considerable differences among patients were observed clinically.

Other hereditary diseases and the liver

In this chapter, an abbreviated account is presented on the subject of hereditary diseases and the liver. However, it is incomplete because Alagille syndrome, storage disorders, alpha-1-antitrypsin deficiency and Wilson disease are not included as they appear in other chapters of this volume. Biliary atresia is omitted because all available evidence does not support any significant genetic association. Molecular biological techniques have enabled linkage of several liver cholestatic disorders to chromosomal loci, and further characterization of the canalicular bile salt transporter (cBST) will advance our understanding of pathogenetic mechanisms involved in benign and progressive cholestatic syndromes. Disorders that have been treated as separate entities may have common 'roots', exemplified by the concept of the ductal plate malformation in fibropolycystic disease. Whereas the majority of disorders referred to in this chapter present early in life, there are several that are associated with liver failure in the neonatal period, which makes early recognition particularly important. Liver transplantation offers a cure for many hereditary disorders affecting the liver but it is not applicable to all.

A gene encoding a P-type ATPase mutated in two forms of hereditary cholestasis

Cholestasis, or impaired bile flow, is an important but poorly understood manifestation of liver disease. Two clinically distinct forms of inherited cholestasis, benign recurrent intrahepatic cholestasis (BRIC) and progressive familial intrahepatic cholestasis type 1 (PFIC1), were previously mapped to 18q21. Haplotype analysis narrowed the candidate region for both diseases to the same interval of less than 1 cM, in which we identified a gene mutated in BRIC and PFIC1 patients. This gene (called FIC1) is the first identified human member of a recently described subfamily of P-type ATPases; ATP-dependent aminophospholipid transport is the previously described function of members of this subfamily. FIC1 is expressed in several epithelial tissues and, surprisingly, more strongly in small intestine than in liver. Its protein product is likely to play an essential role in enterohepatic circulation of bile acids; further characterization of FIC1 will facilitate understanding of normal bile formation and cholestasis.