Form Of Familial Intrahepatic Cholestasis Research Articles

Molecular and Clinical Links between Drug-Induced Cholestasis and Familial Intrahepatic Cholestasis.

Idiosyncratic Drug-Induced Liver Injury (iDILI) represents an actual health challenge, accounting for more than 40% of hepatitis cases in adults over 50 years and more than 50% of acute fulminant hepatic failure cases. In addition, approximately 30% of iDILI are cholestatic (drug-induced cholestasis (DIC)). The liver's metabolism and clearance of lipophilic drugs depend on their emission into the bile. Therefore, many medications cause cholestasis through their interaction with hepatic transporters. The main canalicular efflux transport proteins include: 1. the bile salt export pump (BSEP) protein (ABCB11); 2. the multidrug resistance protein-2 (MRP2, ABCC2) regulating the bile salts' independent flow by excretion of glutathione; 3. the multidrug resistance-1 protein (MDR1, ABCB1) that transports organic cations; 4. the multidrug resistance-3 protein (MDR3, ABCB4). Two of the most known proteins involved in bile acids' (BAs) metabolism and transport are BSEP and MDR3. BSEP inhibition by drugs leads to reduced BAs' secretion and their retention within hepatocytes, exiting in cholestasis, while mutations in the ABCB4 gene expose the biliary epithelium to the injurious detergent actions of BAs, thus increasing susceptibility to DIC. Herein, we review the leading molecular pathways behind the DIC, the links with the other clinical forms of familial intrahepatic cholestasis, and, finally, the main cholestasis-inducing drugs.

Update on Progressive Familial Intrahepatic Cholestasis

Three distinct forms of familial intrahepatic cholestasis are the result of mutations in the ATP8B1, ABCB11, and ABCB4 genes. The pathophysiologies of the latter 2 of these diseases are well characterized and are the result of abnormalities in canalicular excretion of bile acids and phospholipids, respectively. The molecular pathophysiology of the systemic disease associated with mutations in ATP8B1 remains unclear. In all of these diseases, wide variations in clinical phenotypes have been observed. The variability can be ascribed at least in part to predicted genotype:phenotype correlations. Disease- and genotype-specific prognoses and therapeutic approaches may exist, although much more information needs to be ascertained before clinicians can confidently make decisions based on genetic information.

Identification of mutation-prone points in bile salt export pump

Background. The bile salt export pump mediates uphill canalicular bile acid secretion. Inherited dysfunction of the bile salt export pump causes a progressive and a benign form of familial intrahepatic cholestasis. Mutations within the bile salt export pump gene are reported. Presently, prediction of protein nanostructure and function is a great challenge in the proteomics and structural genomics era. Identification of the point vulnerable to mutation is a new trend to expand knowledge on disorders at the genomic and proteomic level of diseases. Materials and methods. A bioinformatic analysis was performed to study the positions that determine peptide motifs in the amino acid sequence of the bile salt export pump. To identify the weak linkage in bile salt export pump, a new bioinformatic tool named GlobPlot was used. Results. The positions 16–34, 119–127, 451–459, 550–561, 1084–1099, 1108–1118, 1135–1140, 1211–1217, and 1314–1321 were identified as the positions prone to mutation. Conclusion. Based on this study, the weak linkages in the bile salt export pump can be identified and can provide good information for expectation of possible new mutations that can lead to cross species jumping. In addition, the results from this study provide useful information for further research on the bile salt export pump.

Impaired expression and function of the bile salt export pump due to three novel ABCB11 mutations in intrahepatic cholestasis

Inherited dysfunction of the bile salt export pump BSEP (ABCB11) causes a progressive and a benign form of familial intrahepatic cholestasis, denominated as PFIC2 and BRIC2, respectively. We functionally characterized novel ABCB11 mutations encountered in two patients with a PFIC2 and a BRIC2 phenotype, respectively. BSEP expression was determined in liver biopsies by immunohistochemistry. ABCB11 mutations were functionally characterized by taurocholate transport in SF9 cells transfected with human ABCB11. The PFIC2 patient was compound heterozygous for a splicing mutation in intron 4 ((+3)A > C) combined with an early stop codon at position 930 (R930X), while the BRIC2 patient was compound heterozygous for two nonsynonymous mutations in exon 9 (E297G) and exon 12 (R432T), respectively. Hepatic BSEP expression was absent in PFIC2 and preserved in BRIC2. In BRIC2, taurocholate transport was decreased to 13% and 20% of reference levels for R432T and E297G, respectively. The intron 4 (+3)A > C, R930X and R432T represent previously undescribed mutations of the ABCB11 gene that confer a PFIC2 and a BRIC2 phenotype, respectively. By combining functional in-vitro characterization with immunohistochemical detection of variant BSEP we provide direct evidence for the role of ABCB11 mutations in the pathogenesis of different forms of intrahepatic cholestasis.

Hepatocellular Transporters and Cholestasis

The secretion of bile is the result of active hepatocellular transport processes, most of which occur across the canalicular membrane of liver cells. Disturbance of the function and/or expression of these transporters leads to the intracellular accumulation of toxic bile acids, thereby promoting cholestatic liver cell injury. Genetically determined alterations of hepatobiliary transporter function are increasingly recognized as important risk factors for an individual's susceptibility to develop cholestasis. It has become evident that, besides the established pathogenic role of mutations in canalicular transporter genes in progressive and benign forms of familial intrahepatic cholestasis, genetics may also play an important role in acquired cholestatic syndromes, such as intrahepatic cholestasis of pregnancy or drug-induced cholestasis. This overview summarizes the physiologic function and regulation of human hepatobiliary transport systems and discusses the impact of their genetic variations for the pathophysiology of different cholestatic syndromes.

Another form of familial intrahepatic cholestasis, another new gene.

Another form of familial intrahepatic cholestasis, another new gene.

Progressive familial intrahepatic cholestasis (PFIC): evidence for genetic heterogeneity by exclusion of linkage to chromosome 18q21-q22.

Progressive familial intrahepatic cholestasis (PFIC) is the second most common form of familial intrahepatic cholestasis. The genes for PFIC and for a milder form of the disease, benign recurrent intrahepatic cholestasis (BRIC), were recently mapped to a 19-cM region on chromosome 18q21-q22. The results suggest that PFIC and BRIC are allelic diseases. We have studied 11 Swedish patients from eight families with clinical and biochemical features consistent with PFIC. The families were genotyped for markers D18S69, D18S64, D18S55 and D18S68, spanning the PFIC candidate region. Unexpectedly, the segregation of haplotypes excluded the entire region in three families, and no indications for shared haplotypes were found in the patients of the six remaining families. A four-point linkage analysis of all families excluded linkage from D18S69 to D18S55 (Zmax < -5). Thus, our data strongly suggest the presence of a second, yet unknown, locus for PFIC. The results indicate that great care should be taken when using 18q markers for prenatal diagnosis and genetic counseling for the disease.

Ocular Ultrasound in Alagille Syndrome: A New Sign

Alagille syndrome (AS) is one of six forms of familial intrahepatic cholestasis, all of which present with neonatal jaundice and paucity of intrahepatic bile ducts. Differentiation of these individual syndromes is crucial as their treatments and prognoses vary. It is the ophthalmic features, posterior embryotoxon on particular, that distinguish AS. The authors performed full ocular examination, including A- and B-scan ultrasound, refraction, and, where possible, fluorescein angiography in 20 unrelated children with AS and 8 with non-AS-related cholestasis. There was ultrasound evidence of optic disc drusen in at least one eye in 95% and bilateral disc drusen in 80% of patients with AS but in none of the patients who were non-AS at the time of examination. Independent review of hard-copy scans suggested drusen in at least one eye in 90% of the cases and bilateral drusen in 50%, although this latter figure rose to 65% on review of the angiograms. This is markedly higher than the incidence in the normal population (0.3%-2%). Axial lengths were shorter than expected for the older age group (older than 10 years of age), but this was not associated with gross ametropia. This strong association of AS and optic disc drusen has not been reported previously and represents not only the first significant association between a systemic condition and disc drusen but also a possibly useful tool in the diagnosis of AS, especially in young children.

ORTHOTOPIC LIVER TRANSPLANTATION FOR BYLER DISEASE

Byler disease is a rare form of familial intrahepatic cholestasis that is fatal before puberty. This retrospective study reviewed the results of orthotopic liver transplantation in 14 children with Byler disease using 12 whole-liver grafts and 2 reduced-size grafts. One post-operative death occurred after retransplantation for arterial thrombosis. In the other patients, infectious problems and rejection episodes were the most frequent complications during the postoperative period. In the 13 patients alive, graft function, growth, and quality of life were good after an average follow-up of 17 months without any sign of disease recurrence.

Hepatocellular Carcinoma in Alagilleʼs Syndrome

Alagille's syndrome is a common form of familial intrahepatic cholestasis. In addition to the hepatobiliary system, many other organ systems are affected. Most of the affected patients survive through adulthood. Hepatic involvement is the cause of death in about one-third of patients. Hepatocellular carcinoma complicating the course of this disease is very rare and has been reported previously in only three cases. We report a family in which three of four siblings with this syndrome developed hepatocellular carcinoma and died as a result of it. None of these children had a liver disease, other than Alagille's syndrome, that could account for the development of such a tumor. This experience suggests that Alagille's syndrome, or at least chronic cholestasis, may be a predisposing factor for the development of hepatocellular carcinoma. Annual determination of alpha-fetoprotein and abdominal computed tomography (CT) scan may detect the development of a hepatocellular carcinoma in such cases while they are still resectable.

Familial intrahepatic cholestatic syndromes.

This discussion has illustrated the enormous variety found within the category of familial intrahepatic cholestasis. It has also demonstrated how much more there is to learn about these fascinating disorders, which may be examples of experiments in nature on bile formation. This analysis should be recognized to be the author's own, and there is much debate about this classification. For example, some workers in this field contend that North American Indian cholestasis is in reality Byler's syndrome. Such an identity seems unlikely, given the differences between the two syndromes (Table 2). This is a field that is changing rapidly. Recently, a new cholestatic syndrome, bearing some similarities to benign recurrent intrahepatic cholestasis, but dissimilar in several ways, has been reported. There is evidence that cholestasis of pregnancy may be inherited as an autosomal dominant, sex-limited trait. If further studies confirm a genetic etiology, this syndrome would be the most common form of familial intrahepatic cholestasis. The assessment of any individual case remains difficult, particularly early in the course. Table 2 can serve as a guide to the differential diagnosis of these conditions. When faced with a neonate with jaundice, all of the usual causes must be ruled out first. The pattern of bile acids in serum is useful for ruling out Zellweger's syndrome. A good family history and physical examination, particularly of the heart, are important. An ophthalmologic examination by a specialist, often under anesthesia, and a spine radiograph can be useful in confirming a diagnosis of Alagille's syndrome. A liver biopsy, carefully interpreted with input from the clinician, is useful in pointing toward one direction or another. Often a firm conclusion cannot be reached, or is reached prematurely, so the clinician would be advised to inform the parents of all diagnostic possibilities in order to avoid false hopes or unwarranted depression. The diagnostic pitfalls to be avoided in this evaluation are many. No histologic findings are clearly pathognomonic for one syndrome or another. Giant cell transformation and paucity of intrahepatic bile ducts may be found in several syndromes. Biliary atresia, or at least failure to demonstrate a patent biliary tree from the liver to the cystic duct, may be present in patients with Alagille's syndrome. In that syndrome, the eye findings, particularly the posterior embryotoxon, may not be appreciated except on extensive ophthalmologic testing, including gonioscopy. Butterfly vertebrae may not be visible at birth and may be no longer evident in adulthood.(ABSTRACT TRUNCATED AT 400 WORDS)