Pediatric Liver Disease

From the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition’s 2009 Annual Meeting

Educational Objectives

The goal of this program is to improve the management of liver disease in children. After hearing and assimilating this pro­gram, the clinician will be better able to:

1.   Recognize neonatal liver failure, based on symptoms, laboratory findings, and liver histology.

2.   Review the genes involved in mitochondrial DNA depletion syndrome.

3.   Describe tests utilized in the diagnosis of acute liver failure.

4.   Discuss the treatment options for the management of intracranial hypertension in hepatic encephalopathy.

5.   List and describe currently available bioartificial liver support devices.

Faculty Disclosure

In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning committee to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of in­terest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, the following has been disclosed: Dr. Rosenthal has received re­search support from Roche, Gilead, and Bristol-Myers Squibb, is on the Speakers’ Bureaus for GlaxoSmithKline and Merck, and is a consultant for HepaLife, Roche, and Salix Pharmaceuticals. Drs. Sokol and Squires and the planning committee re­ported nothing to disclose. In their lectures, Drs. Sokol and Rosenthal present information that is related to the off-label or in­vestigational use of a therapy, product, or device.

Acknowledgments

Drs. Sokol, Squires, and Rosenthal were recorded at North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition’s 2009 Annual Meeting, held November 12-14, 2009, in National Harbor, MD, and sponsored by the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition. The Audio-Digest Foundation thanks the speakers and the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition for their cooperation in the production of this program.

Mitochondrial Liver Disease

Ronald J. Sokol, MD, Professor and Vice Chair, Department of Pediatrics, University of Colorado Denver School of Medicine, and the Children’s Hospital, Aurora, CO

Mitochondrial cytopathies: occur in £1/2000 individuals; involve tissues with high oxidative metabolism in which cells contain large numbers of mitochondria; most prevalent in central nervous system (CNS), peripheral nervous system (PNS), skeletal and cardiac muscle, and liver; lack of mitochondrial function causes adenosine triphosphate depletion and oxidative stress, leading to tissue injury, apoptosis, and necrosis of cells

Mitochondrial hepatopathies: disorders in which dysfunction of hepatocyte mitochondria plays key role in etiology or pathogenesis of liver injury or failure; primary disorders  —  mitochondria primary targets of gene mutation (de­fective critical mitochondrial protein or enzyme); secondary disorders  —  mitochondria target of endogenous or ex­ogenous toxin

Primary mitochondrial hepatopathies: involve respiratory chain disorders or oxidative phosphorylation defects; neonatal liver failure  —  most common; due to specific respiratory chain deficiencies, protein deficiencies, or mitochondrial deple­tion syndrome; later-onset liver dysfunction or failure  —  includes Alpers-Huttenlocher syndrome (AHS), Navajo neuro­hepatopathy (mitochondrial DNA [mtDNA] depletion syndrome), and specific enzyme defects in mitochondria

Neonatal liver failure: typical presentation, with vomiting, hypotonia, and developmental delays; liver function initially not severely affected, but rapid progression to failure seen; laboratory findings  —  high serum lactate (2.0-2.5 mmol/L), increased lactate-to-pyruvate ratio (L/P; >20), hypoglycemia, signs of altered liver synthetic function (eg, increased pro­thrombin time [PT]/international normalized ratio [INR]), and modest increase in aspartate aminotransferase (AST), ala­nine aminotransferase (ALT), and bilirubin; liver histology  —microvesicular steatosis, cholestasis, iron accumulation, and eventually, cirrhosis; abnormalities in cristae and other mitochondrial structures; many patients have normal-looking but excessive numbers of mitochondria per cell; liver biopsy helpful in diagnosis; low respiratory chain enzymes; positive test for mtDNA depletion; imaging possibly abnormal; autosomal recessive inheritance

Alpers-Huttenlocher syndrome (AHS): later-onset disease; abrupt change in previously normal-appearing child; more common in boys; causes vomiting, intractable seizures, and loss of developmental milestones; ataxia, blindness, and death due to involvement of CNS; liver tests moderately abnormal; seizures usually unresponsive to anticonvulsants, and patient frequently placed on valproic acid (affects mitochondria), which precipitates rapid onset of coma and death; characteristic neurologic features seen on autopsy; almost all patients have defect in DNA polymerase gamma gene (POLG; mitochondria-specific DNA polymerase)

Clinical features of mitochondrial hepatopathies: hepatic steatosis (almost all cases); lactic acidosis in many but not all; ketosis in some; liver failure in many; multisystem disease suggests mitochondrial etiology; causes failure to thrive; most of diseases caused by mutations in nuclear genes (control replication, transcription, translation, and repair of mtDNA; can result in insufficient mtDNA [mtDNA depletion]); may also involve other organs

mtDNA depletion syndrome: abnormally low levels of mtDNA, but normal levels of nuclear DNA; impaired synthesis of mtDNA or abnormal pathway for regeneration of deoxynucleosides (necessary for mtDNA replication); leads to abrupt decrease in respiratory chain function; 2 forms, ie, hepatocerebral and myopathic; liver not involved in myopathic form; 9 associated genes have been identified (3 associated with hepatic failure); deoxyguanosine kinase (dGUOK) deficiency  —  probably most common cause of neonatal liver failure in patients with lactic acidosis; nystagmus common, usually hypo­tonic; DGUOK gene controls protein involved in salvage of deoxynucleoside; mutations specific to family (>40 known; no common mutation); must sequence entire gene; some patients mildly affected and able to survive without liver trans­plantation, with mild neurologic problems; liver transplantation offers no advantage in patients with neurologic involve­ment; hepatocellular carcinoma (HCC) seen in some patients who survived without liver transplantation; survival without liver transplantation good in patients without neurologic features; those with neurologic features succumb within 2 yr; POLG deficiency  —  if POLG gene abnormal, not enough DNA produced, leading to depletion of mitochondrial respira­tory chain elements; all cases of AHS and isolated cases of neonatal liver failure have genetic basis; normal serum lactate seen in ³50% of patients; liver transplantation contraindicated because CNS involvement almost always present; Navajo neurohepatopathy  —  PNS disease caused by mutation in MPV17 gene that codes for mitochondrial inner membrane pro­tein; mtDNA depleted; liver involved in all patients; isolated cases with only liver involvement described; poor results seen in those who underwent liver transplantation (neurologic findings developed after transplantation if not present be­fore); TRMU deficiency  —  gene controls mtDNA translation; mitochondria-specific transfer RNA (tRNA) thiol-modify­ing enzyme that depends on presence of cysteine and sulfur groups; proposed that between 1 and 4 mo of age, before cystathionase activity starts and decreasing metallothionein levels seen, infant susceptible to liver failure (not before and not after)

Screening: best single test plasma lactate >2.5 mmol/L if patient not in shock and L/P ratio >20 (not seen in many patients); magnetic resonance (MR) spectroscopy helpful; proton spectroscopy can define lactate peaks in brain and cerebrospinal fluid (CSF; portends CNS involvement); imaging necessary if considering liver transplantation; respiratory chain enzyme analysis requires frozen liver muscle fibroblast biopsy; if mitochondrial liver disease highly suspected, obtain genotyping within 2 wk (rather than biopsy); tissue or circulating white blood cells tested for mtDNA depletion; complete mtDNA sequencing available but not necessary

Treatment: support oxidative metabolism by removing or detoxifying drug or toxin and using metabolic substrates or antioxidants; vitamin E, coenzyme Q10 and carnitine used without evidence of benefit; liver transplantation in carefully selected patients; future therapy  —  supplementation with nucleosides or small molecules; correction of enzyme defect; genetic therapy; liver transplantation  —  considered if complete evaluation (including MR proton spectroscopy to rule out lactate peak in brain) indicates disease limited to liver; better outcome probable in patients with dGUOK deficiency (with no other tissue involvement); contraindicated in those with POLG and MPV17 defi­ciencies and Navajo neurohepatopathy; inform family (regardless of presence of extrahepatic involvement before transplantation) of possible evolution after transplantation

Recognition and Referral for Acute Liver Failure

Robert H. Squires Jr, MD, Professor of Pediatrics, University of Pittsburgh School of Medicine, and Clinical Direc­tor, Gastroenterology, Children’s Hospital of Pittsburgh, University of Pittsburgh Medical Center, Pittsburgh, PA

Definition of acute liver failure (ALF): acute hepatic dysfunction, jaundice, and encephalopathy (development within 8 wk)

Tests: PT used to assess coagulation factors; INR  —  more uniform; determined from patient’s PT, normal PT, and inter­national sensitivity index (assigned by manufacturer of tissue factor used to determine PT); better measure across sites for uniformity; PT and INR developed for vitamin K antagonists and not designed to assess ALF; not good marker for bleeding risk; bleeding episodes occur from imbalance between pro- and anticoagulants; renal failure, portal hyperten­sion, or sepsis may precipitate imbalance; study suggested that determining liver histology of no benefit in treatment; severity of necrosis may not predict potential recovery

ALF Study Group: outcome in patients with stage 0, 1, 2, 3, or 4 encephalopathy at presentation; 34% of patients without encephalopathy at presentation died or received transplant; 38% of those with stage 4 encephalopathy sur­vived; difficult to predict outcome and determine transplant candidacy; study  —  93 infants <4 wk of age with ALF; indeterminate rate significantly increases beyond 4 wk; indeterminate viral hepatitis and iron storage disease com­mon in this age group; indeterminate viral hepatitis seen in 60% of ALF patients between 1 and 5 yr of age; acet­aminophen toxicity dominant diagnosis in patients >10 yr of age; in those <7 mo of age, indeterminate viral hepatitis due to herpes, cytomegalovirus, and Epstein-Barr virus; of 830 patients with ALF, only 5 with acute hepa­titis A; metabolic disease dominates in patients 5 yr of age, Wilson’s disease predominant in those >5 yr of age; mi­tochondrial disease seen across all age groups; tyrosinemia seen beyond infancy; urea cycle defects also seen across all age groups; drug-induced liver disease  —  no effective way to identify; if diagnosis not known, transplantation performed more often; almost 45% of patients in indeterminate group not tested for metabolic disease; need age-appropriate diagnostic prioritization for potentially treatable patients to exclude them from transplantation; from in­fectious standpoint, in patients <8 wk of age, consider herpesvirus, enterovirus, and adenovirus (likelihood of hep­atitis A, B, and C small; obtain serologies from mother); testing for metabolic disease, obtaining drug history, and looking for vascular anatomic abnormalities important

Management of Acute Liver Failure

Philip Rosenthal, MD, Professor of Pediatrics and Surgery, University of California, San Francisco, School of Medi­cine, Medical Director, Pediatric Liver Transplant Program, and Director, Pediatric Hepatology, University of Cali­fornia, San Francisco, Children’s Hospital

Acute liver failure: approach using team from gastroenterology, hepatology, neurology, transplant surgery, and in­tensive care unit (ICU) provides best results; timely diagnosis crucial; early referral to transplant center imperative

Neurologic assessment: frequent monitoring required in hepatic encephalopathy (HE); pediatric ICU indicated if pa­tient in stage 2 or early stage 3 coma; difficult to determine in infants, so electroencephalography (EEG) plays role; 25% risk for cerebral edema in patients with stage 3 HE; seizures may herald cerebral edema; computed tomogra­phy (CT) sometimes normal early in course

Management of intracranial hypertension: head-of-bed elevation; hyperventilation (effect wears off with time); osmotherapy  —  mannitol; not 100% effective; wears off over time; worsens edema if blood-brain barrier damaged; new and controversial therapies include use of hypertonic saline in mild hypothermia, plasmapheresis, and barbitu­rate infusions; hypertonic saline  —  may restore osmotic gradient across astrocyte membrane and improve micro­vascular blood flow by reducing endothelial swelling; possibly more effective than mannitol; maintain serum sodium at 145 to 155 mEq/L; in study, reducing intracranial pressure did not result in survival advantage; hypothermia  —  data from animal models; whole body cooling to 32 to 35°C; reduces cerebral blood flow and con­centration of ammonia in CSF; may improve brain oxidative metabolism of glucose and decrease cytokines; suc­cessful in uncontrolled trials; does not increase risk for infection; total plasma exchange  —  corrects coagulopathy and removes cytokines and hepatotoxins; results in »30% reduction in arterial ammonia; may replace with fresh frozen plasma; no anticoagulation necessary; may use in chronic viral-B hepatitis (CVBH) and serve as possible bridge to therapy

N-acetylcysteine (NAC): intravenous (IV) NAC proven antidote for acetaminophen toxicity; can improve hemody­namics in ALF; Adult United States ALF Study Group  —IV NAC vs placebo for nonacetaminophen ALF; primary outcome overall survival at 3 wk; secondary outcomes included spontaneous (transplant-free) survival, transplanta­tion rate, length of ICU or hospital stay, and number of organ system failures; expected results  —  spontaneous sur­vival in placebo group »25% vs 45% in NAC group; overall survival »57% in placebo group vs 75% in NAC group; actual results  —  no difference in overall survival at 3 wk between NAC and placebo; advantage seen in transplant-free survival, specifically in grades 1 and 2 encephalopathy; trend for fewer transplantations in NAC group (not sta­tistically significant), with shorter lengths of stay; no difference in serious adverse events between 2 groups (more nausea and vomiting seen in NAC group); conclusion  —  IV NAC should be considered for adult patients with early stages of ALF, but not substitute for early referral for transplantation; adults with late-stage disease typically sur­vive only 4 days without transplantation; NAC use in children  —  acute acetaminophen toxicity still only indication; awaiting results of trial looking at NAC for nonacetaminophen ALF

Cell-based approaches to ALF: hepatocyte transplantation; extracorporeal devices; implantable constructs; trans­genic xenografts; hepatocycte transplantation  —  minimally invasive alternative to organ transplantation; stem cell-derived hepatocyctes delivered to liver to populate or injected into spleen; fetal or adult hepatocytes used; must be fresh (not cryopreserved); require ³109 hepatocytes for efficacy; <40 patients treated so far; of 11 children (3 wk to 16 yr of age) treated with conventional immunosuppression for drug, idiopathic, or viral ALF, 20% recovered with­out liver transplantation and 30% as bridge to liver transplantation; however, assessment difficult

Bioartificial liver support devices: molecular adsorbents recirculation system (MARS)  —  approved by Food and Drug Administration; used for drug overdose and poisoning; efficacy decreases over time unless filters changed; extracorporeal liver assist device (ELAD)  —  use of C3A hepatoblastoma cell line problematic (potential for hepa­toblastoma if cells escape device and enter patient); Chinese study demonstrated statistically significant improve­ment in transplant-free survival for chronic and ALF patients (mostly with hepatitis B) treated with ELAD; not currently approved for use; HepaMate system  —  third-generation; 2 clinical trials using cryopreserved porcine he­patocytes demonstrated survival without transplant; reduced risk for pretransplantation death in fulminant hepatic failure; benefit seen in patient survival and maintenance of neurologic status before, during, and immediately after transplant; improved survival in fulminant hepatic failure patients with drug-induced liver toxicity; study showed 77% 30-day survival, compared to 51% survival with standard of care

Volume 24, Issue 07   April 7, 2010

Pediatric Liver Disease

From the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition’s 2009 Annual Meeting

Mitochondrial Liver Disease

Ronald J. Sokol, MD, Professor and Vice Chair, Department of Pediatrics, University of Colorado Denver School of Medicine, and the Children’s Hospital, Aurora, CO

Mitochondrial cytopathies: occur in £1/2000 individuals; involve tissues with high oxidative metabolism in which cells contain large numbers of mitochondria; most prevalent in central nervous system (CNS), peripheral nervous system (PNS), skeletal and cardiac muscle, and liver; lack of mitochondrial function causes adenosine triphosphate depletion and oxidative stress, leading to tissue injury, apoptosis, and necrosis of cells

Mitochondrial hepatopathies: disorders in which dysfunction of hepatocyte mitochondria plays key role in etiology or pathogenesis of liver injury or failure; primary disorders  —  mitochondria primary targets of gene mutation (de­fective critical mitochondrial protein or enzyme); secondary disorders  —  mitochondria target of endogenous or ex­ogenous toxin

Primary mitochondrial hepatopathies: involve respiratory chain disorders or oxidative phosphorylation defects; neonatal liver failure  —  most common; due to specific respiratory chain deficiencies, protein deficiencies, or mitochondrial deple­tion syndrome; later-onset liver dysfunction or failure  —  includes Alpers-Huttenlocher syndrome (AHS), Navajo neuro­hepatopathy (mitochondrial DNA [mtDNA] depletion syndrome), and specific enzyme defects in mitochondria

Neonatal liver failure: typical presentation, with vomiting, hypotonia, and developmental delays; liver function initially not severely affected, but rapid progression to failure seen; laboratory findings  —  high serum lactate (2.0-2.5 mmol/L), increased lactate-to-pyruvate ratio (L/P; >20), hypoglycemia, signs of altered liver synthetic function (eg, increased pro­thrombin time [PT]/international normalized ratio [INR]), and modest increase in aspartate aminotransferase (AST), ala­nine aminotransferase (ALT), and bilirubin; liver histology  —microvesicular steatosis, cholestasis, iron accumulation, and eventually, cirrhosis; abnormalities in cristae and other mitochondrial structures; many patients have normal-looking but excessive numbers of mitochondria per cell; liver biopsy helpful in diagnosis; low respiratory chain enzymes; positive test for mtDNA depletion; imaging possibly abnormal; autosomal recessive inheritance

Alpers-Huttenlocher syndrome (AHS): later-onset disease; abrupt change in previously normal-appearing child; more common in boys; causes vomiting, intractable seizures, and loss of developmental milestones; ataxia, blindness, and death due to involvement of CNS; liver tests moderately abnormal; seizures usually unresponsive to anticonvulsants, and patient frequently placed on valproic acid (affects mitochondria), which precipitates rapid onset of coma and death; characteristic neurologic features seen on autopsy; almost all patients have defect in DNA polymerase gamma gene (POLG; mitochondria-specific DNA polymerase)

Clinical features of mitochondrial hepatopathies: hepatic steatosis (almost all cases); lactic acidosis in many but not all; ketosis in some; liver failure in many; multisystem disease suggests mitochondrial etiology; causes failure to thrive; most of diseases caused by mutations in nuclear genes (control replication, transcription, translation, and repair of mtDNA; can result in insufficient mtDNA [mtDNA depletion]); may also involve other organs

mtDNA depletion syndrome: abnormally low levels of mtDNA, but normal levels of nuclear DNA; impaired synthesis of mtDNA or abnormal pathway for regeneration of deoxynucleosides (necessary for mtDNA replication); leads to abrupt decrease in respiratory chain function; 2 forms, ie, hepatocerebral and myopathic; liver not involved in myopathic form; 9 associated genes have been identified (3 associated with hepatic failure); deoxyguanosine kinase (dGUOK) deficiency  —  probably most common cause of neonatal liver failure in patients with lactic acidosis; nystagmus common, usually hypo­tonic; DGUOK gene controls protein involved in salvage of deoxynucleoside; mutations specific to family (>40 known; no common mutation); must sequence entire gene; some patients mildly affected and able to survive without liver trans­plantation, with mild neurologic problems; liver transplantation offers no advantage in patients with neurologic involve­ment; hepatocellular carcinoma (HCC) seen in some patients who survived without liver transplantation; survival without liver transplantation good in patients without neurologic features; those with neurologic features succumb within 2 yr; POLG deficiency  —  if POLG gene abnormal, not enough DNA produced, leading to depletion of mitochondrial respira­tory chain elements; all cases of AHS and isolated cases of neonatal liver failure have genetic basis; normal serum lactate seen in ³50% of patients; liver transplantation contraindicated because CNS involvement almost always present; Navajo neurohepatopathy  —  PNS disease caused by mutation in MPV17 gene that codes for mitochondrial inner membrane pro­tein; mtDNA depleted; liver involved in all patients; isolated cases with only liver involvement described; poor results seen in those who underwent liver transplantation (neurologic findings developed after transplantation if not present be­fore); TRMU deficiency  —  gene controls mtDNA translation; mitochondria-specific transfer RNA (tRNA) thiol-modify­ing enzyme that depends on presence of cysteine and sulfur groups; proposed that between 1 and 4 mo of age, before cystathionase activity starts and decreasing metallothionein levels seen, infant susceptible to liver failure (not before and not after)

Screening: best single test plasma lactate >2.5 mmol/L if patient not in shock and L/P ratio >20 (not seen in many patients); magnetic resonance (MR) spectroscopy helpful; proton spectroscopy can define lactate peaks in brain and cerebrospinal fluid (CSF; portends CNS involvement); imaging necessary if considering liver transplantation; respiratory chain enzyme analysis requires frozen liver muscle fibroblast biopsy; if mitochondrial liver disease highly suspected, obtain genotyping within 2 wk (rather than biopsy); tissue or circulating white blood cells tested for mtDNA depletion; complete mtDNA sequencing available but not necessary

Treatment: support oxidative metabolism by removing or detoxifying drug or toxin and using metabolic substrates or antioxidants; vitamin E, coenzyme Q10 and carnitine used without evidence of benefit; liver transplantation in carefully selected patients; future therapy  —  supplementation with nucleosides or small molecules; correction of enzyme defect; genetic therapy; liver transplantation  —  considered if complete evaluation (including MR proton spectroscopy to rule out lactate peak in brain) indicates disease limited to liver; better outcome probable in patients with dGUOK deficiency (with no other tissue involvement); con