Figure 13.1 Diagram of mechanisms of bile flow. Cartoon depiction of hepatocyte couplet with vectorial flow of bile from sinusoidal blood to bile canaliculus via basolateral and canalicular transporters. (Reproduced with permission from Kleinman RE, et al., Walker’s Pediatric Gastrointestinal Disease, 6th ed., People’s Medical Publishing House, Shelton, CT, 2015.)

Table 13.1 Summary of biliary transport diseases

The FIC1 protein is expressed in a variety of tissues, including pancreas, small intestine, stomach, bladder, heart, placenta, lung, liver, colon and kidney, with greatest expression in pancreas and intestine [8,27–29]. Immunohistochemistry shows that FIC1 is expressed on the apical surface of many of these cells and has expression in bile duct epithelium, which may be relevant for the hepatic manifestations of the disease [27,28,30]. Expression in the intestine appears to be along the entire length of the small intestine.

Given the broad tissue distribution of FIC1, it is reasonable to ask why patients with FIC1 disease are diagnosed with cholestasis, rather than a more systemic disease. The development of cholestasis as the seemingly primary feature of FIC1 disease is likely explained by a relative lack of proteins that can replace the function of FIC1 in the liver or a greater sensitivity of the liver, in comparison with other organs, to loss of FIC1 function. It is also becoming clear, however, that FIC1 deficiency does encompass extrahepatic features, consistent with an important role for FIC1 in a number of tissues, thus resembling a syndromic disorder.

In many ways, the biochemical markers in FIC1 disease are quite similar to those seen in BSEP disease, including relatively normal transaminase levels, variably elevated bilirubin levels depending upon the phase of the disease and normal cholesterol and γ-GT levels; however, serum transaminase, bile salt and serum albumin levels tend to be lower in patients with FIC1 disease than in those with BSEP disease, while serum alkaline phosphatase is higher [13,21,31–33]. Severe and sometimes disabling diarrhoea and malabsorption may also be present, as may, more rarely, pancreatic insufficiency or pancreatitis. Wheezing and elevated sweat chloride levels have been described in some patients with FIC1 disease [33,34]. An elevated prevalence of hearing loss has also been reported in FIC1 disease, as has resistance to parathyroid hormone [19,31,33,35].

Findings of light and transmission EM suggest that, at presentation, patients with FIC1 disease tend to manifest bland intracanalicular cholestasis with coarsely granular bile, termed Byler bile, in contrast to findings of ‘neonatal hepatitis’ and amorphous bile in patients with BSEP disease [32]. Immunohistochemical analysis of γ-GT and neutral endopeptidase (CD10) in FIC1 patient liver suggests a dearth of these ectoenzymes in the canalicular membrane of hepatocytes in patients with severe FIC1 disease [36,37].

13.3.1  Bile salt export pump deficiency

The genetic defect in BSEP was initially determined by studying a subset of Saudi Arabian patients with PFIC and led to the identification of the ABCB11 gene [38,39]. A number of gene mutations in ABCB11 have been described [13,40–47]. Physiologic function of BSEP is evident by the types of mutations present. BSEP mutations may result in the severe, progressive disease; intermittent disease; or non-progressive disease (or diseases of intermediate severity, such as in drug-induced cholestasis [DIC] and intrahepatic cholestasis of pregnancy [ICP]) [48–52]. Disease mutations in BSEP encompass a variety of mutation types, including missense, nonsense, deletions, insertions and splice site mutations. Most of these mutations result in greatly reduced or absent BSEP staining at the bile canaliculus [47] (Figure 13.2). Several BSEP mutations may affect the processing and stability of the protein [49,53].

The diagnosis of a defect in BSEP should be suspected in any infant or young child with cholestasis, usually manifest by pruritus, who has normal serum γ-GT and cholesterol levels. Biliary bile salt levels have been reported to be very low; however, this is typically unavailable for routine clinical analysis. Cholestasis in patients with severe BSEP disease is often manifest by pruritus and jaundice early in life, typically before 1 year of age. The inability of infants to scratch may translate into irritability as a first feature of this disorder. Biochemical findings are consistent with progressive intrahepatic cholestasis (Table 13.1). Studies of children with BSEP disease demonstrate hepatocellular cholestasis, canalicular bile plugs and centrizonal/sinusoidal fibrosis, often with periportal fibrosis. Portal fibrosis has been noted to worsen over time. Transmission EM shows canalicular dilatation, microvilli loss, abnormal mitochondrial internal structure and varying intracanalicular accumulation of finely granular bile [54]. Immunohistochemical assessment of hepatic γ-GT and other canalicular markers reveals strong staining at the bile canaliculus, in contrast to the diminished staining observed in FIC1 disease. Given the key role of BSEP in bile formation, it is not surprising that the clinical progression of liver disease in patients with severe mutations is relatively rapid.

Genotype–phenotype correlations in BSEP disease are becoming clearer. Patients with homozygous protein truncating mutations or missense mutations often have severe and relentlessly progressive disease. A subset of patients may have mutations in BSEP that lead to a partially active protein that may show defects in protein trafficking or stability [55,56]. These patients may have a more moderate disease course and could potentially be amenable to nontransplant surgical interventions like partial biliary diversion or ileal bypass [33]. An intermittently symptomatic phenotype has been described in partially inactivating mutations, which some have referred to as BRIC2 [42,43,57]. Unlike mild FIC1 disease, cholelithiasis has been observed in a number of the patients with mild BSEP disease [21,33,42]. Hepatic expression of BSEP may be quite variable and related to polymorphisms in BSEP [58]. Several studies have evaluated possible correlation between different mutations in BSEP and the spectrum of disease, from severe and progressive (PFIC) through intermittent and nonprogressive (BRIC), and including ICP [21,33,48,59,60]. Hepatocellular carcinoma (HCC) has been identified in many children with severe BSEP disease, with the largest study showing malignancy in 15% of patients. HCC has also been identified even in patients with biochemical and symptomatic improvement following partial external biliary diversion (PEBD). Protein-truncating mutations conferred particular risk compared with less severe genotypes [44,47]. Other malignancies in children with BSEP disease have been described, including cholangiocarcinoma and pancreatic adenocarcinoma [61,62]. With the exception of tyrosinaemia, this is an unprecedented number of cases of liver-related malignancies in a paediatric population. As such, clinicians must consider the increased risk of cancer in decision-making and surveillance procedures for children with BSEP disease.

Figure 13.2 Immunohistochemical staining in BSEP deficiency. Three images from a PFIC2 patient’s liver biopsy at presentation. (a) No immunostaining of BSEP is present. (b) The distorted canalicular network is visible in material immunostained for the Dubin–Johnson protein (multidrug resistance–associated protein 2 [MRP2]). (c) Giant cell hepatitis is apparent. (d) Normal control from a patient without cholestasis haematoxylin/eosin, anti-BSEP antibody (diaminobenzidine chromogen [DAB])/haematoxylin (two images), anti-MRP2 antibody (DAB)/haematoxylin (one image); all images 200× original magnification. (From Kleinman RE, et al., Walker’s Pediatric Gastrointestinal Disease, 6th ed., People’s Medical Publishing House, Shelton, CT, 2015. With permission from Dr. Alex Knisely.)

Surgical approaches that utilise depletion of the bile salt pool can be effective in some BSEP patients and involve significantly less risk than liver transplantation. Transplant is a good option for children with severe BSEP deficiency and should be considered in patients with progressive liver dysfunction or who continue to have symptoms of pruritus, cholestasis, liver cirrhosis and growth retardation, despite receiving external biliary diversion [63]. Outcomes of living donor liver transplantation for BSEP disease are quite good [64,65]. Patients with BSEP disease have shown good graft survival with rapid increase in growth acceleration [66]. Further studies show that patients with BSEP deficiency have significant catch-up growth after transplantation [67]. Hepatocyte transplantation has been proposed for BSEP disease, but studies are still preliminary [68].

Recently, recurrence of low-γ-GT cholestasis in patients with BSEP deficiency who have had liver transplant have been reported. Keitel et al. reported the first case of a child with BSEP disease suffering from repeated posttransplant recurrence of progressive intrahepatic cholestasis due to autoantibodies against BSEP [69]. These antibodies occurred after transplantation and were detected in the patient’s serum and at the canalicular membrane of two consecutive liver transplants. The antibodies inhibited transport activity of BSEP, thus causing severe cholestasis. The patient had missense changes in the BSEP gene which resulted in the complete absence of BSEP, possibly accounting for the lack of tolerance towards BSEP in this patient after transplant, causing autoantibody formation towards BSEP [69]. Siebold et al. described the clinical course of six patients who developed recurrent low γ-GT cholestasis, mimicking BSEP disease, following transplantation. All had documented genetic defects in ABCB11 that were predicted to lead to a congenital absence of BSEP protein. The time to development of recurrence was variable; four underwent repeat transplantation for complications of recurrent disease, and all four developed recurrent disease after retransplantation, with three ultimately dying, two as a direct result of complications of their liver disease [70]. The liver biopsies in these patients showed canalicular cholestasis, giant hepatocytes and slight lobular fibrosis, without evidence of rejection or biliary complications [71]. Remission of these episodes may be achieved by intensifying the immunosuppressive regimen [72]. Clinicians should be aware of the possibility of recurrence in this population.

Differentiation of BSEP from FIC1 disease may be difficult; two studies of relatively large patient samples have provided insight on this topic [21,33]. Being a member of the Amish community is highly suggestive, but not diagnostic of FIC1 disease [73]. The slower clinical progression of FIC1 disease may help distinguish it from defects in BSEP. At presentation, patients with BSEP deficiency have higher serum aminotransferase, bile salt, albumin and α-fetoprotein levels, and lower alkaline phosphatase values, than do FIC1 disease patients; BSEP deficiency patients are also more likely to have elevated white blood cell counts. Patients with BSEP deficiency are more likely to demonstrate giant cells or multinucleate cells at liver biopsy and negative staining for BSEP upon liver immunohistochemistry, and are more prone to gallstone disease, portal hypertension, HCC and early liver failure. In contrast, patients with FIC1 disease tend to have more extrahepatic symptoms [21,33]. Exocrine pancreatic function and serum pancreatic enzymes are normal in patients with BSEP deficiency [74,75]. The characteristic EM appearance of bile (with the patient off ursodeoxycholic acid [UDCA] therapy) is highly suggestive of this FIC1 disease. Immunostaining of BSEP may rapidly identify whether diagnostic sequencing of ABCB11 should be performed [21,76]. The ultrastructural appearance of canalicular bile in patients who are not receiving UDCA may differentiate BSEP from FIC1 disease [32]. Localisation of canalicular markers like γ-GT may also be useful. A number of commercial tests are now widely available. Denaturing high-performance liquid chromatography (DHPLC) and gene resequencing chip technology have been used to identify mutations in ABCB11 [2,77]. Accuracy in assigning an appropriate diagnosis may be imperative, since patients with BSEP deficiency appear to respond well to liver transplantation, while those with FIC1 disease may not, and may require a more specialised surgical approach. In addition, the apparent increased risk of HCC in BSEP disease may necessitate surveillance or early liver transplantation in some patients.

The clinical consequences of a correct diagnosis are related to the appropriate choice of therapy. FIC1 deficiency is a systemic disease, and liver transplantation is not necessarily curative. Persistent diarrhoea, graft steatosis, growth failure and pancreatitis have all been observed after liver transplantation in children with FIC1 disease [16,20,64,65,78]. Instead, surgical approaches that utilise depletion of the bile salt pool can be effective in some FIC1 disease patients and involve significantly less risk than liver transplantation. Bezafibrate treatment favourably affected pruritus, dyslipidaemia and cholestasis in patients with severe FIC1 deficiency [79]. Use of pharmacologic chaperones such as 4-phenylbutyrate has also been proposed for treatment of patients with FIC1 mutations [80]. Clearly, at this time, surgical approaches are the treatment of choice for compensated FIC1 disease.

13.4  SURGICAL APPROACHES TO PFIC

Surgical approaches that utilise depletion of the bile salt pool can be effective in some PFIC disease patients and involve significantly less risk than liver transplantation. The principle was first reported in 1947 by Richard Varco,^* who reported use of a cholecystostomy for pruritus in ‘chronic disorders of the liver’, long before PFIC was actually described [81]. These methods now include principally partial biliary diversion and ileal bypass [82–89]. Both techniques lead to wasting of bile salts and presumed depletion of toxic bile salts, although this explanation of the therapeutic effect is likely incomplete. Interruption of the enterohepatic circulation may ameliorate some of the problems associated with possible gain of function in the ileal bile acid transporter. Both treatments have been shown to markedly improve pruritus and to stabilise or even improve both the biochemical and histological manifestations of the disease [90] (Box 13.2).

13.4.1  Partial external biliary diversion

PEBD involves creating a short (5–10 cm) free jejunal loop just distal to the ligament of Treitz.^† This isoperistaltic loop is anastomosed to the fundus of the gallbladder proximally, and the distal end is brought out as an end stoma (Figure 13.3). The stoma should be in the right lower quadrant to facilitate placement of a stomal appliance preventing bile seepage onto the skin. The stoma must be carefully everted to allow the appliance to fit as effectively as possible in providing a tight seal around the stoma. Seepage of bile can be extremely irritating to the child, and frustrating to the caregivers. Stomal problems can be a source of major morbidity even if the primary symptoms are improved. It is estimated that about 50% of bile is wasted by external diversion.

Stay updated, free articles. Join our Telegram channel

Join