Bile Acid Synthetic Defects and Liver Disease: A Comprehensive Review

Bile acid synthetic defects (BASD), uncommon genetic disorders that are responsible for approximately 2% of persistent cholestasis in infants, are reviewed with emphasis on morphology of associated liver disease. The associated liver diseases may be life threatening, and are treatable, usually by replacement of deficient primary bile acids. Specific diagnosis is made by analysis of body fluids (bile, blood, and urine) using fast atom bombardment-mass spectroscopy (FAB-MS) and gas chromatography-mass spectroscopy (GC-MS). Inborn errors have been demonstrated for four single enzymes involved in modification of the sterol nucleus and in five steps in modification of the side-chain to form cholic and chenodeoxycholic acids, the primary bile acids. With few exceptions, BASD cause liver diseases that vary from severe to mild depending on the defect. In three of four known defects of sterol nucleus modification, liver disease is progressive. Progression of liver disease is most rapid when the defect results in accumulation of toxic monohydroxy and unsaturated oxo-bile acids. Liver disease may be transient, delayed in onset and mild. Reduced bile flow caused by atypical bile acids contributes to cholestasis and may be the dominant factor in defects of side-chain synthesis, peroxisomal abiogenesis and S-L-O syndrome. Pathological findings may include intralobular cholestasis with giant cell transformation, prevalence of necrotic hepatocytes including giant cell forms, and hepatitic injury confined to the portal limiting plate where the smallest bile ductules may be injured and where fibrosis typically develops. Interlobular bile ducts are usually spared. Ultrastructure of liver reveals nonspecific changes with the possible exception of unusual canalicular morphology in some defects. The course of BASD may be modified by replacement of deficient primary bile acids, which produces beneficial feedback inhibition of abnormal bile acid production and enhances choluresis. Giant cell transformation is present in all symptomatic infants with BASD and seems to have a more consistent association with BASD than with the many other liver diseases in infants where it occurs. We hypothesize that immature hepatocytes of infants may fuse to form multinucleate hepatocytes whenever atypical or toxic bile acids are present and the pool of normal bile acids is critically reduced. This review was supported by NCRR, NIH grant RR-08084.     

Mutation in the sterol 27-hydroxylase gene associated with fatal cholestasis in infancy

BACKGROUND: Inborn errors of bile acid synthesis are rare but potentially treatable causes of neonatal cholestasis. We here present a cholestatic infant with an ongoing cytomegalovirus infection who despite intensive treatment died of severe liver disease at 4 months of age. METHODS: The urinary steroids were investigated by electrospray mass spectrometry and gas chromatography mass spectrometry. Oxysterols in plasma were analysed by isotope dilution mass spectrometry. Mutations in the sterol 27-hydroxylase gene were detected by PCR. RESULTS: Glucuronidated bile alcohols, which are known to be excreted by patients with cerebrotendinous xanthomatosis (CTX) were detected in the urine. Analysis of plasma revealed markedly reduced levels of 27-hydroxycholesterol. Mutation analysis showed the presence of a stop codon in exon 7, confirming the diagnosis of CTX, a rare disease not previously diagnosed in Sweden. CONCLUSIONS: Fetal and neonatal deaths among siblings of patients with CTX have been reported previously and the present case supports the contention that reduced activity of the sterol 27-hydroxylase may predispose to the development of neonatal cholestasis. The associated viral infection may have further precipitated the liver disease. Since CTX, like other inborn errors of bile acid synthesis may be treated with bile acids an early diagnosis is essential. Thus, the analysis of urine by electrospray mass spectrometry is highly recommended in the investigation of patients with neonatal cholestasis.     

Metabolic disorders presenting as liver disease

A wide range of inherited metabolic disorders lead to biochemical disturbances within the liver. A number of disorders of energy metabolism present as hepatomegaly with hypoglycaemia e.g. glycogen storage diseases or with hypoketotic hypoglycaemia e.g. disorders of fat oxidation. Other defects of carbohydrate metabolism also present with hypoglycaemia and liver disease either in neonates e.g. galactosaemia and fructose-1,6-bisphosphatase deficiency or at weaning i.e. hereditary fructose intolerance. Mitochondrial respiratory chain defects frequently present in neonates/infants as liver disease but often there is other (multi)-organ involvement and persistent lactic acidaemia. Many disorders of peroxisomal and lysosomal metabolism cause a spectrum of liver dysfunction. Urea cycle disorders manifest as hyperammonaemia often presenting acutely in neonates but also in older children and adults. Other causes of liver disease include disorders of copper, bile acid and bilirubin metabolism. Definitive diagnosis requires specialist expertise, however once clinical liver disease is apparent, most disorders are associated with characteristic findings on routine laboratory testing that should raise the suspicion of metabolic disease.     

Liver disease in cystic fibrosis

Liver involvement in Cystic Fibrosis (CF) is much less frequent than both pulmonary and pancreatic diseases that are present in 80-90% of CF patients; liver disease (LD) affects only one third of CF patients, however, because of the decreasing mortality from extrahepatic causes, its recognition and management is becoming a relevant clinical issue. Recent observations suggest that clinical expression of LD in CF may be influenced by genetic modifiers; their identification is an important issue because it may allow recognition of patients at risk for the development of LD at the time of diagnosis of CF and early institution of prophylactic strategies. Oral bile acid therapy, aimed at improving biliary secretion in terms of bile viscosity and bile acid composition, is currently the only available therapeutic approach for CF-associated LD. However, the impact of this therapy on the natural history of LD remains to be defined and long-term effectiveness on clinically relevant outcomes should be further investigated. Liver transplantation should be offered to CF patients with progressive liver failure and/or with life-threatening sequelae of portal hypertension, who also have mild pulmonary involvement that is expected to support long-term survival. The 1-year survival rate after transplantation in CF patients is approximately 80%, with beneficial effects on lung function, nutritional status, body composition and quality of life in most cases.     

Treatment of chronic liver disease caused by 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase deficiency with chenodeoxycholic acid.

Deficiency of 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase, the second enzyme in the sequence that catalyses the synthesis of bile acids from cholesterol, leads to chronic liver disease in childhood as well as to malabsorption of fat and fat soluble vitamins. A 4 year old boy with this condition has been successfully treated by oral administration of a bile acid--chenodeoxycholic acid. He had been jaundiced since birth, grew poorly because of rickets, and had severe pruritus. Plasma transaminase activities were persistently raised. Chenodeoxycholic acid 125 mg twice daily for two months, and then 125 mg daily, cured his jaundice and pruritus, returned his transaminase activities to normal, and eliminated the need for calcitriol for prevention of rickets. On this treatment he has so far remained well for two years. A diagnosis of 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase deficiency should be considered in any child with unexplained chronic hepatitis or cirrhosis, especially if the liver disease is accompanied by a clinically obvious malabsorption of fat soluble vitamins. A simple colorimetric test of the urine confirms the diagnosis and effective treatment can be started.     

Neonatal cholestasis

The spectrum of diseases causing neonatal cholestasis presents intriguing problems for future investigation. There are many causes, and the eventual outcome of the specific entity has unique individual features, despite the wide areas of overlap. For example, extrahepatic biliary atresia may be the result of the sporadic occurrence of a virus-induced, progressive obliteration of the extrahepatic bile ducts with some degree of intrahepatic bile duct injury. This same sequence of viral infection with persisting injury may account for sporadic (nonfamilial) cases of neonatal hepatitis, as suggested by the Landing hypothesis. Conversely, the familial forms of cholestasis, either neonatal hepatitis or instances of intrahepatic cholestasis, are most likely genetic diseases that represent specific defects in the hepatic excretory process or in the bile secretory apparatus. The persistent nature of these presumed enzymatic or structural defects may explain the less favorable prognosis. Elucidation of the nature of these inborn errors of liver function may allow a better understanding of biliary physiology, and improved therapy.     

Potential etiologies of biliary atresia

Biliary atresia is the most common cause of neonatal cholestasis and the leading indication for pediatric liver transplantation worldwide. The disease is caused by a progressive inflammatory and fibrosing obliteration of the extrahepatic bile ducts. Although the cause of this obstruction is largely unknown, patient-based studies have identified environmental and genetic factors that may interact and orchestrate disease pathogenesis. Chief among these factors are infectious and immunologic processes. While infectious agents have varied in different patient populations, studies of liver specimens at different phases of disease point to a pro-inflammatory commitment of lymphocytes at the time of diagnosis, and to their potential role in regulating bile duct obstruction. A review of these studies is the focus of this article.     

Clinical approach to inherited metabolic disorders in neonates: an overview

There are almost one hundred inborn errors of metabolism which can start in the neonatal period, but less than 20 are amenable to treatment. In general, an extremely evocative clinical setting is the course of a full-term baby born after normal pregnancy and delivery who, after an initial symptom-free period deteriorates relentlessly for no apparent reason and does not respond to symptomatic therapy. Investigations routinely performed in all sick neonates yield normal results. Emergency treatment must be undertaken in parallel with investigations. Five main presentations can be observed: a neurologic deterioration ‘intoxication’ type mostly suggests maple syrup urine disease, methylmalonic, propionic, isovaleric acidaemias and urea cycle disorders. Isolated seizures is the revealing symptom of pyridoxine-responsive and folinic acid responsive seizures. A jaundice or a liver failure suggest galactosaemia, fructosaemia, tyrosinaemia type I (after 3 weeks), phosphomannoisomerase deficiency or bile acid synthesis defects. Cardiac failure and heartbeat disorders should first suggest mitochondrial fatty acid oxidation (FAO) disorders. Persistent hypoglycaemia is the presenting sign of glyco/ gluconeogeneis defects, hyperinsulinism and FAO disorders. The first line investigation relies upon the collection at the same time of a few samples including blood gases electrolytes, prothrombin time, transaminases, ammonia and lactic acid, and the search for ketonuria. The storage of plasma, urine and blood (on filter paper) is an important element in the diagnosis. The utilization of these samples should be carefully planned after taking advice from specialists in inborn errors.     

Hepatic function and physiology in the newborn

The liver develops from progenitor cells into a well-differentiated organ in which bile secretion can be observed by 12 weeks' gestation. Full maturity takes up to two years after birth to be achieved, and involves the normal expression of signalling pathways such as that responsible for the JAG1 genes (aberrations occur in Alagille's syndrome), amino acid transport and insulin growth factors. At birth, hepatocytes are already specialized and have two surfaces: the sinusoidal side receives and absorbs a mixture of oxygenated blood and nutrients from the portal vein; the other surface delivers bile and other products of conjugation and metabolism (including drugs) to the canalicular network which joins up to the bile ductules. There is a rapid induction of functions such as transamination, glutamyl transferase, synthesis of coagulation factors, bile production and transport as soon as the umbilical supply is interrupted.Anatomical specialization can be observed across the hepatic acinus which has three distinct zones. Zone 1 borders the portal tracts (also known as periportal hepatocytes) and is noted for hepatocyte regeneration, bile duct proliferation and gluconeogenesis. Zone 3 borders the central vein and is associated with detoxification (e.g. paracetamol), aerobic metabolism, glycolysis and hydrolysis and zone 2 is an area of mixed function between the two zones.Preterm infants are at special risk of hepatic decompensation because their immaturity results in a delay in achieving normal detoxifying and synthetic function. Hypoxia and sepsis are also frequent and serious causes of liver dysfunction in neonates.Stem cell research has produced many answers to the questions about liver development and regeneration, and genetic studies including studies of susceptibility genes may yield further insights. The possibility that fatty liver (increasingly recognized as non-alcoholic steatohepatitis or NASH) may have roots in the neonatal period is a concept which may have important long-term implications.     

The changing pattern of diagnosis of infantile cholestasis

OBJECTIVE: Cholestatic liver disease in infancy is caused by a wide range of conditions. This study reviews the pattern of diagnosis of infants with cholestasis presenting to a tertiary referral paediatric hospital in Sydney, Australia, during a 12-year period (1985-96). METHODOLOGY: Infants aged less than 6 months with cholestasis were identified retrospectively from hospital records and data retrieved from the medical records. RESULTS: There were 205 infants identified as having cholestatic liver disease. The aetiology of the cholestasis was idiopathic in 25%, metabolic/genetic in 23%, and due to obstruction in 20%, parenteral nutrition in 20%, infection in 9% and bile duct hypoplasia in 3%. CONCLUSIONS: This study highlights the changing patterns of diagnosis of cholestatic liver disease in infants at a tertiary paediatric facility, demonstrating that up to 50% of cases are now due to genetic/metabolic diseases or parenteral nutrition, and a high proportion are due to idiopathic disease.     

Diagnostic determination system for high-risk screening for inborn errors of bile acid metabolism based on an analysis of urinary bile acids using gas chromatography–mass spectrometry: Results for 10 years in Japan

Background:  Some patients with cholestasis of unknown cause may have inborn errors of bile acid metabolism (IEBAM) thus causing abnormalities of bile acid biosynthesis. Although seven types of bile acid synthetic defects have thus far been reported for this disorder, no detailed information on its incidence and so on in Japan is yet available. In order to elucidate the current status of IEBAM in Japan, in July 1996 a diagnostic determination system was established for high-risk screening for IEBAM.
Methods:  Urinary bile acids were analyzed on gas chromatography–mass spectrometry (GC-MS) and quantitative analysis was done using selected ion monitoring (SIM).
Results and conclusions:  In a total of 576 samples analyzed over the 10 year period prior to June 2005, 159 patients were found with cholestasis of unknown etiology. Of these patients, 10 (6.3%) were found to have IEBAM by this system, while 91 (61.1%) had cholestasis without a definitive diagnosis. This diagnostic determination system with GC-MS of urinary bile acids is therefore considered useful for detecting IEBAM.     

Neonatal cholestatic syndromes associated with alterations in bile acid synthesis

In summary, the conditions discussed above are examples of diseases that result in deficient bile acid synthesis and production of abnormal bile acids. Although the relationship between the production of these abnormal bile acids and the pathogenesis of these diseases remains unknown, they continue to provide us with a better understanding of normal pathways of bile acid production. Clearly, more studies are needed before these interesting metabolic defects and normal infantile bile acid metabolism itself are well understood.     

Caroli's disease in children: Is it commonly misdiagnosed?

Aim: Caroli's disease is a simple form of intrahepatic bile duct ectasia. It can be complicated with the involvement of liver parenchyma and portal hypertension. Herein, the difficult management of delayed presentation of Caroli's disease is reported. Methods and results: We report on four different forms of clinical presentation of Caroli's disease: an infant with fulminant liver failure, a teenager with persistent biliary fistula, a boy with hypersplenism in the face of portal hypertension and a girl with variceal bleeding.

Conclusions: Caroli's disease must be included in the differential diagnosis of cystic lesions in the liver. Delayed diagnosis of Caroli's disease is difficult to manage and appropriate investigations are warranted before planning a surgical approach.     

Gallensäuren- und Gallelipidtransportdefekte

Bile acid- and bile lipid transporter defects are a heterogenous group of disorders characterized by familiarity, early onset with rapid progression to chronic end stage liver disease without bile duct anomalities. They are so called progressive familial intrahepatic cholestasis (PFIC). Today 3 types are known. Type 1 corresponds to “Byler disease” and is found in Amish people. It is characterized by high serum concentration of bile acids but low catalytic serum concentration of gGT. There is one mild variant of this disorder, the benign recurrent intrahepatic cholestasis (BRIC). PFIC-2 has the same clinical chemical findings and is observed in non-Amish people. It is called Byler syndrome. PFIC-3 is characterized by familiarity, high serum bile acids and in contrast to type 1 and 2 high catalytic serum concentration of γGT. Again, a mild variant has been found, the cholestasis of pregnancy. Therapeutic options are partial biliary diversion in PFIC-1 and 2 in the early stage. If this surgical therapy fails or if there is already a cirrhosis, liver transplantation is needed. Some patients with PFIC-3 respond to ursodesoxycholic acid therapy, the rest needs liver transplantation as well.     

Dysmorphology: an approach to a child with structural defects

An approach to children with structural defects has been presented. The ultimate goal of this approach is a specific overall diagnosis. In such cases appropriate genetic counseling for the parents, accurate prognostication relative to the child's future development and an appropriate plan to help the child reach his potential usually are possible. When an overall diagnosis is lacking, the most that can be expected is a better understanding of the nature and onset of the problem. That in itself can often be helpful to patients and to all others dealing with children having structural defects.     

RECENT ADVANCES IN THE UNDERSTANDING OF GENETIC CAUSES OF CONGENITAL HEART DEFECTS

The clinical approach to children with congenital heart defects (CHD) has been revolutionized during the past four decades by developments in diagnostics and therapeutics. In contrast, a profound understanding of the causes of the majority of CHD has only begun to emerge within the past few years. Prior epidemiological studies suggested that Mendelian disorders constituted a very small percentage of CHD and that polygenic inheritance was responsible for the majority of cases. Recent discoveries, largely achieved with molecular genetic studies, have provided new insights into the genetic basis of heart malformations. These studies have shown that CHD caused by single gene or single locus defects is more common than had been suspected. In addition, a higher percentage of heart malformations occur in the context of familial disease than was evident previously. In this review, molecular genetic studies of specific heart lesions and syndromes with CHD are reviewed. Progress on the Human Genome Project has accelerated identi cation of genes for Mendelian traits with heart defects, and it is anticipated that disease genes for most single gene traits will be known within a few years. Future challenges include utilizing this emerging genetic information to improve diagnosis and treatment of children with CHD, and harnessing the power of genomics to analyze isolated heart defects with complex inheritance patterns.     

Bile salt export pump gene mutations in two Japanese patients with progressive familial intrahepatic cholestasis

BACKGROUND: In recent years, progressive familial intrahepatic cholestasis has been classified into at least three types by genetic analysis: PFIC1, PFIC2, and MDR3. Liver transplantation is effective for treating patients with this intractable syndrome. Confirming the correct diagnosis is of paramount importance because prognosis after transplantation differs with the genetic type of the disease. METHODS: Synthesis of cDNA was accomplished using RNA extracted from liver tissue of two Japanese patients with progressive familial intrahepatic cholestasis. Polymerase chain reaction was performed using 13 primer sets designed for amplification of the bile salt export pump cDNA. Direct sequencing was undertaken, and identified sequences were compared with the sequence for bile salt export pump gene registered with GenBank. In addition, gene sequences for nonprogressive familial intrahepatic cholestasis patients were analyzed. RESULTS: Genetic analysis of patient 1 revealed that substitutions in bile salt export pump protein sequences, namely R575X and E636G, might be the cause of the disease. In patient 2, V330X and R487H might fulfill the same role. Results of gene analysis in parents and cholestatic controls supported these conclusions. CONCLUSIONS: Absence or presence of bile salt export protein gene mutations was confirmed as representing a useful prognostic marker for clinical course after liver transplantation.     

Effects of ursodeoxycholic acid therapy for liver disease associated with cystic fibrosis

The hydrophilic bile acid ursodeoxycholic acid (UDCA) has recently been shown to improve indexes of liver function in adult patients with various liver diseases. The clinical and biochemical responses to UDCA administration (10 to 15 mg/kg body weight per day) were therefore investigated in nine patients with cystic fibrosis and evidence of liver disease. All patients were receiving pancreatic enzymes and taurine supplementation. Liver function tests were done and serum bile acid concentrations and biliary bile acid composition were determined before and during UDCA therapy; fat balance studies and fecal bile acid excretion were carried out before and 6 months after UDCA treatment. After 2 months of bile acid therapy, biliary bile acid composition was enriched in UDCA from approximately 5% before treatment to 25%, at the expense of cholic and chenodeoxycholic acids, thus making the pool more hydrophilic. This enrichment is lower than that reported for adults with chronic liver diseases. Serum concentrations of UDCA increased significantly but variably. UDCA became the predominant fecal bile acid excreted (12% to 67%), indicating a variable absorption of the administered bile acid. Liver function improved in all patients after 2 to 6 months of therapy, although the degree of improvement (aspartate aminotransferase, -34%; alanine aminotransferase, -41%; gamma-glutamyltranspeptidase, -41% alkaline phosphatase, -19%) was lower than that observed in adults with chronic liver diseases. Mean coefficient of fat absorption and growth rate were, on average, unaffected by UDCA therapy, although an improvement was noted for three patients with greater severity of steatorrhea. The study indicates that UDCA can be used safely in this patient population but that higher doses of UDCA may be of greater benefit in the treatment of the liver disease associated with cystic fibrosis.     

Surgery for biliary tract problems in children

Jaundice in the neonate is common and when not associated with symptoms or signs of systemic illness may at first be regarded with some complacency by both mother and health professional alike. When the cholestatic nature of the jaundice becomes apparent, a cause must be identified, if possible within 2 weeks of onset. Biliary atresia, choledochal cyst, inspissated bile syndrome and spontaneous perforation of the bile duct are the most frequent surgical causes. An investigation protocol includes stool observation, ultrasound scanning, biochemical liver function tests, a screen for infective and metabolic causes, a radioisotope excretion scan (hydroxyiminodiacetic acid HIDA scan) and, if necessary, operative cholangiogram and liver biopsy. Surgical management, if performed timeously, may prevent progression of parenchymal disease and in many cases can be curative. Delayed diagnosis leads to inevitable progression of liver damage with a poor long-term outlook. Cholelithiasis is being seen more frequently both in the infant and older child. Surgical intervention is required for symptomatic disease and for stones in the common bile duct. Tumours of the bile ducts are rare but are most likely to be malignant and should be referred to specialist centres for management.     

先天性胆汁酸合成障碍2型一家系临床和遗传学分析:两个AKR1D1新突变的识别

先天性胆汁酸合成障碍2型(CBAS2)是编码Δ4-3-氧固醇5β-还原酶的AKR1D1基因突变导致的常染色体隐性遗传病,以胆汁淤积性黄疸为主要临床表现,伴脂肪和脂溶性维生素吸收障碍。本文报道了1例CBAS2患儿的临床特点及AKR1D1基因突变分析结果。患儿为8个月男婴,因发现全身皮肤、巩膜黄染7月余就诊。体查发现患儿发育、营养差;皮肤、巩膜轻度黄染;肝右肋下8 cm,质地中等,脾脏不大。血生化结果发现转氨酶和总胆红素升高,以结合胆红素升高为主,但γ-谷氨酰转肽酶和总胆汁酸水平基本正常。肝脏组织学检查见胆管排列紊乱,多核巨细胞易见,肝细胞内明显淤胆,伴间质纤维组织增生及淋巴细胞浸润。代谢性肝病组套二代测序及Sanger测序验证结果证实患儿AKR1D1基因型为c.579+2del T/c.853CT(p.Q285X),两个突变均为新突变,且分别来源于其母亲和父亲。患儿最终确诊为CBAS2,给予鹅去氧胆酸治疗后,肝功能明显好转,肝肿大逐渐改善。3个月后随访,肝脏右肋下2.5 cm可及,质软,肝功能各项指标已恢复正常。