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BACKGROUNDLiver disease in urea cycle disorders (UCDs) ranges from hepatomegaly and chronic hepatocellular injury to cirrhosis and end-stage liver disease. However, the prevalence and underlying mechanisms are unclear.METHODSWe estimated the prevalence of chronic hepatocellular injury in UCDs using data from a multicenter, longitudinal, natural history study. We also used ultrasound with shear wave elastography and FibroTest to evaluate liver stiffness and markers of fibrosis in individuals with argininosuccinate lyase deficiency (ASLD), a disorder with high prevalence of elevated serum alanine aminotransferase (ALT). To understand the human observations, we evaluated the hepatic phenotype of the AslNeo/Neo mouse model of ASLD.RESULTSWe demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD. In addition, ultrasound with shear wave elastography and FibroTest revealed increased echogenicity and liver stiffness, even in individuals with ASLD and normal aminotransferases. The AslNeo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen noted before death (3-5 weeks of age). This excessive hepatic glycogen is associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase and is rescued with helper-dependent adenovirus expressing Asl using a liver-specific (ApoE) promoter.CONCLUSIONOur results link urea cycle dysfunction and impaired hepatic glucose metabolism and identify a mouse model of liver disease in the setting of urea cycle dysfunction.TRIAL REGISTRATIONThis study has been registered at ClinicalTrials.gov (NCT03721367, NCT00237315).FUNDINGFunding was provided by NIH, Burroughs Wellcome Fund, NUCDF, Genzyme/ACMG Foundation, and CPRIT.

Objectives: Hepatocellular carcinoma (HCC) has been linked to chronic viral or metabolic liver disease and other conditions. The characteristics of children with HCC have not been fully elucidated and outcomes in children with predisposing liver disease are not well defined., Methods: Patients ≤21 years old with HCC managed at our institution and through external consultation between 1996 and 2016 were included. Demographics, clinical history, and pathology were tabulated. Fisher exact test and Wilcoxon test were employed for subgroup comparison, and survival differences were evaluated by Kaplan-Meier method., Results: Sixty-one cases of HCC were identified. Seven of 16 patients (44%) at our institution and 18 of 45 consult patients (40%) had a predisposing condition: cryptogenic cirrhosis/steatosis (9), genetic (7), biliary pathology (4), viral hepatitis (1), and other (4). Thirteen of 27 patients with de novo HCC had fibrolamellar HCC. Clinical characteristics were grouped by presence or absence of predisposing conditions: age at diagnosis (7.2 vs 10.2 years, P < 0.05), metastatic disease at presentation (15% vs 44%, P = n.s), and tumor size >4 cm (20% vs 100%, P < 0.05). In patients treated at our institution, 5 of 7 with predisposing conditions received liver transplant and achieved complete remission, whereas only 3 of 9 patients with de novo HCC received curative surgery and this group had decreased median overall survival (P < 0.05)., Conclusions: The majority of children with HCC did not have predisposing liver or associated disease. These patients were diagnosed later with more advanced stage disease and had significantly decreased overall survival.

Objectives: Systematic study of allograft liver histology in children undergoing orthotopic liver transplantation (LT) for cystic fibrosis-related liver disease (CFLD)., Methods: Retrospective clinicopathologic review of explants and allograft liver biopsies from 13 children and adolescents with CFLD., Results: In this study, the median age at LT for CFLD was 15.7 years. Notably, 10 of 13 (77%) CF explants had >5% steatosis and 8 of 13 (61.5%) demonstrated variable fibrosis. The median age, sex, type of transplant (liver vs liver-lung), pancreatic insufficiency status, body mass index (BMI) percentile, genotype, and prevalence of diabetes were comparable in those with and without explant steatosis. More than half of allograft biopsies showed significant steatosis (17/31, 54.8%) and lobular inflammation (16/31, 51.6%). Hepatocyte ballooning was less frequent (5/31, 16.1%). Overall, 6 patients (46.2%) had allograft steatosis that worsened over time in 2 patients (33%). None had advanced fibrosis (≥stage 3). Patients with allograft steatosis had significantly more biopsies, were more likely to be "liver only" recipients, had a shorter interval since transplant and higher body mass index percentile (although <85). Patients without explant steatosis never demonstrated allograft steatosis, whereas 60% of patients with explant steatosis (n = 6) developed varying degrees of allograft steatosis. The degree of explant steatosis did not predict its severity in allografts (P = 0.3)., Conclusion: This is the first study highlighting the development of allograft steatosis in CF patients. Our findings suggest that allograft steatosis in patients with CF may be related to pre-existing steatosis in native livers, regardless of other risk factors and may have implications on patient management and long-term graft/patient survival.

Liver disease in the neonate, infant, child, and adolescent may manifest differently depending on the type of disorder. These disorders show marked overlap clinically and on light microscopy. Histology and ultrastructural examination are used in tandem for the diagnosis of most disorders. A final diagnosis or interpretation of the pediatric liver biopsy depends on appropriate and adequate clinical history, laboratory test results, biochemical assays, and molecular analyses, as indicated by the light microscopic and ultrastructural examination., (Copyright © 2017 Elsevier Inc. All rights reserved.)

A tribute to Pepper's lasting contributions to Hepatopathology., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Hepatocellular carcinoma (HCC) represents a classic example of inflammation-linked cancer. To characterize the role of the immune system in hepatic injury and tumor development, we comparatively studied the extent of liver disease and hepatocarcinogenesis in immunocompromised versus immunocompetent Fah-deficient mice. Strikingly, chronic liver injury and tumor development were markedly suppressed in alymphoid Fah(-/-) mice despite an overall increased mortality. Mechanistically, we show that CD8(+) T cells and lymphotoxin β are central mediators of HCC formation. Antibody-mediated depletion of CD8(+) T cells as well as pharmacological inhibition of the lymphotoxin-β receptor markedly delays tumor development in mice with chronic liver injury. Thus, our study unveils distinct functions of the immune system, which are required for liver regeneration, survival, and hepatocarcinogenesis., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The C19MC gene on chromosome band 19q13.4 encodes a cluster of 46 microRNAs; those microRNAs are normally only expressed from the paternal allele and in the placenta. Placental expression correlates with selective demethylation of the paternal C19MC promoter, in contrast to methylation of both maternal and paternal alleles in nonplacental tissues. Prior investigations demonstrated "ectopic" activation of this gene in most hepatic mesenchymal hamartomas, including sporadic tumors and others with androgenetic-biparental mosaicism (subset of cells are diploid, but contain only paternally derived chromosomes). In the present investigation of C19MC promoter methylation status in a series of 14 mesenchymal hamartomas, a demethylated allele was identified in 6 tumors, including all 4 with androgenetic-biparental mosaicism. Conversely, only methylated alleles were cloned from sporadic hamartomas, including 3 tumors with chromosomal rearrangements thought likely to activate C19MC expression independent of the native promoter. In conjunction with published data, the findings suggest multiple molecular mechanisms for C19MC activation in hepatic mesenchymal hamartoma, including the existence of a normal placental imprinting pattern in mesenchymal cells in a subset of cases. Some or all of the latter hamartomas may result from placental "grafting," a hypothesis supported by endothelial expression of the placental vascular marker, glucose transporter-1, in 1 of the 6 cases with a demethylated allele.

Hereditary tyrosinemia type I (HT1) is caused by deficiency in fumarylacetoacetate hydrolase (FAH), an enzyme that catalyzes the last step of tyrosine metabolism. The most severe form of the disease presents acutely during infancy, and is characterized by severe liver involvement, most commonly resulting in death if untreated. Generation of FAH(+/-) pigs was previously accomplished by adeno-associated virus-mediated gene knockout in fibroblasts and somatic cell nuclear transfer. Subsequently, these animals were outbred and crossed to produce the first FAH(-/-) pigs. FAH-deficiency produced a lethal defect in utero that was corrected by administration of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione (NTBC) throughout pregnancy. Animals on NTBC were phenotypically normal at birth; however, the animals were euthanized approximately four weeks after withdrawal of NTBC due to clinical decline and physical examination findings of severe liver injury and encephalopathy consistent with acute liver failure. Biochemical and histological analyses, characterized by diffuse and severe hepatocellular damage, confirmed the diagnosis of severe liver injury. FAH(-/-) pigs provide the first genetically engineered large animal model of a metabolic liver disorder. Future applications of FAH(-/-) pigs include discovery research as a large animal model of HT1 and spontaneous acute liver failure, and preclinical testing of the efficacy of liver cell therapies, including transplantation of hepatocytes, liver stem cells, and pluripotent stem cell-derived hepatocytes., (Copyright © 2014. Published by Elsevier B.V.)

Total parenteral nutrition (TPN) is associated with the development of parenteral nutrition-associated liver disease (PNALD) in infants. Fish oil-based lipid emulsions can reverse PNALD, yet it is unknown if they can prevent PNALD. We studied preterm pigs administered TPN for 14 days with either 100% soybean oil (IL), 100% fish oil (OV), or a mixture of soybean oil, medium chain triglycerides (MCTs), olive oil, and fish oil (SL); a group was fed formula enterally (ENT). In TPN-fed pigs, serum direct bilirubin, gamma glutamyl transferase (GGT), and plasma bile acids increased after the 14 day treatment but were highest in IL pigs. All TPN pigs had suppressed hepatic expression of farnesoid X receptor (FXR), cholesterol 7-hydroxylase (CYP7A1), and plasma 7α-hydroxy-4-cholesten-3-one (C4) concentrations, yet hepatic CYP7A1 protein abundance was increased only in the IL versus ENT group. Organic solute transporter alpha (OSTα) gene expression was the highest in the IL group and paralleled plasma bile acid levels. In cultured hepatocytes, bile acid-induced bile salt export pump (BSEP) expression was inhibited by phytosterol treatment. We show that TPN-fed pigs given soybean oil developed cholestasis and steatosis that was prevented with both OV and SL emulsions. Due to the presence of phytosterols in the SL emulsion, the differences in cholestasis and liver injury among lipid emulsion groups in vivo were weakly correlated with plasma and hepatic phytosterol content.

The role of the pathologist in dealing with common problems of liver disease in children is likely to change dramatically as the molecular genetic revolution progresses. For example, microchip arrays for genes involved in bile salt synthesis and transport will pinpoint the specific mutations responsible for infantile cholestasis and similar methods will sort out infectious agents of acute and chronic hepatitis. But even as biochemistry, microbiology, and immunology laboratories already provide essential diagnostic information in such settings, informed histopathologic interpretation will continue to guide investigations of etiology and therapeutics and will remain an important medical necessity [95,96,100,102,104].

Background: Tributyltin (TBT) is a persistent and bioaccumulative environmental toxicant. Developmental exposure to TBT has been shown to cause fatty liver disease (steatosis), as well as increased adiposity in many species, leading to its characterization as an obesogen. Objective: We aimed to determine the long-term effects of developmental TBT exposure on the liver. Methods: C57BL/6J mice were exposed to a dose of TBT (0.5 mg/kg body weight per day; 3.07 [micro]M) below the current developmental no observed adverse effect level (NOAEL) via drinking water, or drinking water alone, provided to the dam from preconception through lactation. Sires were exposed during breeding and lactation. Pups from two parity cycles were included in this study. Animals were followed longitudinally, and livers of offspring were analyzed by pathological evaluation, immunohistochemistry, immunoblotting, and RNA sequencing. Results: Developmental exposure to TBT led to increased adiposity and hepatic steatosis at 14 and 20 weeks of age and increased liver adenomas at 45 weeks of age in male offspring. Female offspring displayed increased adiposity as compared with males, but TBT did not lead to an increase in fatty liver or tumor development in female offspring. Liver tumors in male mice were enriched in pathways and gene signatures associated with human and rodent nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). This includes down-regulation of growth hormone receptor (GHR) and of STAT5 signaling, which occurred in response to TBT exposure and preceded liver tumor development. Conclusions: These data reveal a previously unappreciated ability of TBT to increase risk for liver tumorigenesis in mice in a sex-specific manner. Taken together, these findings provide new insights into how early life environmental exposures contribute to liver disease in adulthood. https://doi.org/10.1289/EHP5414, Introduction Environmental exposures during development have emerged as a significant risk factor for liver disease (Foulds et al. 2017). Some of the clearest demonstrations of the impact of early life [...]

CCAAT/Enhancer Binding Proteins family proteins are important regulators of liver functions. Here, we show the critical role of C/EBPα-mediated chromatin remodeling in the age-associated dysfunctions of the liver and in the maintenance of physiological homeostasis. Because ph-S193 isoform of C/EBPα is increased in livers of old mice, we have generated C/EBPα-S193D knockin mice, which mimic the ph-S193 isoform of C/EBPα. Analyses of these mice showed that the S193D mutation causes chromatin remodeling leading to histological appearance of ‘foci-like’ nodules, which are also observed in livers of old mice. These ‘foci-like’ structures contain K9 trimethylated histone H3, a marker of heterochromatin. The increase of heterochromatin regions in S193D mice correlates with the elevation of S193D-C/EBPα-HDAC1 complexes and with dys-regulation of gene expression including epigenetic silencing of cyclin D1 and D2 promoters and the inhibition of liver proliferation. The elimination of C/EBPα-HDAC1 complexes in S193D mice by inhibition of HDAC1 corrects chromatin structure and normalizes expression of cyclin D1 and D2. We found that epigenetic dys-regulation is also associated with the elevation of C/EBPβ and with the increase of C/EBPα/β heterodimers in S193D mice. The C/EBPα/β heterodimers activate transcription of Glut4 and increase the levels of Glut4. As the result, S193D livers have accelerated uptake of glucose and accumulation of glycogen in the liver. Thus, this study demonstrates that the phosphorylation of C/EBPα at S193 leads to the appearance of heterochromatin regions, which correlates with the development of age-related dysfunctions of the liver. [ABSTRACT FROM AUTHOR]

How organ size is controlled in mammals is not currently understood. In Drosophila the Hippo signaling pathway functions to suppress growth in imaginal discs and has been suggested to control organ size. To investigate the role of hippo signaling in regulation of mammalian organ size we have generated conditional alleles of Sav1, mst1, and mst2, orthologs of Drosophila Salvador and hippo, respectively. Specific deletion of both mstl and mst2 in hepatocytes results in significantly enlarged livers due to excessive proliferation. By the age of 5-6 months, mst1/2 conditional mutant livers have multiple foci of liver tumors, indicating that the combined activjties of mst1 and mst2 act as redundant tumor suppressors in hepatocytes. Similar findings were obtained with liver-specific deletion of Sav1, a second core Hippo signaling component that facilitates activation of mstl and mst2. Tumors from savi mutants exhibited varied morphology, suggesting a mixed-lineage origin of tumor-initiating cells. Transcriptional profiling of liver tissues from both mst1/2 and savi conditional mutants revealed a network of Hippo signaling regulated genes with specific enrichment for genes involved in immune and inflammatory responses. Histâlogical and immunological characterization of mst1/2 double mutant liver tissues revealed abundant accumulation of adult facultative stem cells termed oval cells in periductal regions. Because oval cells induction is commonly associated with liver injury and tumorformation, it is likely that these cells contribute to the enlarged livers and hepatomas that we observe in savi and mst1/2 mutants. Taken together, our results demonstrate that the Hippo signaling pathway is a critical regulator of mammalian liver growth and a potent suppressor of liver tumor formation. [ABSTRACT FROM AUTHOR]

Liver repopulation with bone marrow-derived hepatocytes (BMHs) can cure the genetic liver disease fumarylacetoacetate hydrolase (Fah) deficiency. BMHs emerge from fusion between donor bone marrow-derived cells and host hepatocytes. To use such in vivo cell fusion efficiently for therapy requires knowing the nature of the hematopoietic cells that fuse with hepatocytes. Here we show that the transplantation into Fah-/- mice of hematopoietic stem cells (HSCs) from lymphocyte-deficient Rag1-/- mice, lineage-committed granulocyte-macrophage progenitors (GMPs) or bone marrow-derived macrophages (BMMs) results in the robust production of BMHs. These results provide direct evidence that committed myelomonocytic cells such as macrophages can produce functional epithelial cells by in vivo fusion. Because stable bone marrow engraftment or HSCs are not required for this process, macrophages or their highly proliferative progenitors provide potential for targeted and well-tolerated cell therapy aimed at organ regeneration. [ABSTRACT FROM AUTHOR]

Presenting characteristics, long-term outcome, and techniques used in the diagnosis of 143 infants with suspected biliary obstruction are reviewed. Sixty-nine patients had surgically confirmed extrahepatic disease and 74 had intrahepatic disorders. A disproportionate number of infants with intraphepatic disease were boys (p = 0.013), low birthweight (p = 0.001), or had siblings with liver disease (p = 0.017). An initial total bilirubin of 20 mg/dl or greater was rare except in the intrahepatic disease category of neonatal hepatitis of known cause (p = 0.006). The initial percutaneous liver biopsy correctly predicted the ultimate diagnosis in 94 percent of all 143 patients. A methodological outline to diagnosis is presented, emphasizing early recognition of symptoms and careful follow-up with hepatobiliary imaging, liver biopsy, and surgical exploration, if required, until definitive diagnosis is made. This approach has aided us in reducing the age of diagnosis of biliary atresia from 12.8 ± SD 7.3 weeks during the period 1971 through 1979 to 6.8 ± SD 2.6 weeks from 1980 to 1982 (p = 0.0015). Eighteen-month survival has improved from 25 to 60 percent. [ABSTRACT FROM AUTHOR]

Syncytial giant cell hepatitis (SGCH) has recently been reported to be a cause of severe hepatitis, with little chance of patient recovery without orthotopic liver transplantation. We have recently seen a patient with multisystem disease and histologic features of SGCH. Upon reaching stage IV coma, she was treated with an extracorporeal liver assist device containing 200 g of cultured liver cells. There was an immediate improvement in her galactose elimination capacity, and her own liver recovered to the point that therapy could be discontinued after 58 h. The patient recovered slowly from her multisystem disease and was discharged with mildly elevated transaminases and biochemical evidence of homeostasis. All laboratory values are normal at 2 yr, and the patient appears to have no sequelae of her disease. [ABSTRACT FROM AUTHOR]

Wilson's disease (WD) is an autosomal recessive disorder that results in accumulation of copper in the liver as a consequence of mutations in the gene encoding the copper-transporting P-type ATPase (ATP7B). WD is a chronic liver disorder, and individuals with the disease present with a variety of complications, including steatosis, cholestasis, cirrhosis, and liver failure. Similar to patients with WD, Atp7b-/- mice have markedly elevated levels of hepatic copper and liver pathology. Previous studies have demonstrated that replacement of zinc in the DNA-binding domain of the estrogen receptor (ER) with copper disrupts specific binding to DNA response elements. Here, we found decreased binding of the nuclear receptors FXR, RXR, HNF4α, and LRH-1 to promoter response elements and decreased mRNA expression of nuclear receptortarget genes in Atp7b-/- mice, as well as in adult and pediatric WD patients. Excessive hepatic copper has been described in progressive familial cholestasis (PFIC), and we found that similar to individuals with WD, patients with PFIC2 or PFIC3 who have clinically elevated hepatic copper levels exhibit impaired nuclear receptor activity. Together, these data demonstrate that copper-mediated nuclear receptor dysfunction disrupts liver function in WD and potentially in other disorders associated with increased hepatic copper levels. [ABSTRACT FROM AUTHOR]

Hepatic glucose production is critical for basal brain function and survival when dietary glucose is unavailable. Glucose-6-phosphatase (G6Pase) is an essential, rate-limiting enzyme that serves as a terminal gatekeeper for hepatic glucose release into the plasma. Mutations in G6Pase result in Von Gierke's disease (glycogen storage disease-1a), a potentially fatal genetic disorder. We have identified the transcriptional coactivator SRC-2 as a regulator of fasting hepatic glucose release, a function that SRC-2 performs by controlling the expression of hepatic G6Pase. SRC-2 modulates G6Pase expression directly by acting as a coactivator with the orphan nuclear receptor RORα. In addition, SRC-2 ablation, in both a whole-body and liver-specific manner, resulted in a Von Gierke's disease phenotype in mice. Our results position SRC-2 as a critical regulator of mammalian glucose production. [ABSTRACT FROM AUTHOR]

Summary: Accumulation of toxic metabolites in hereditary tyrosinemia type I (HT1) patients leads to chronic DNA damage and the highest risk for hepatocellular carcinomas (HCCs) of any human disease. Here we show that hepatocytes of HT1 mice exhibit a profound cell-cycle arrest that, despite concomitant apoptosis resistance, causes mortality from impaired liver regeneration. However, additional loss of p21 in HT1 mice restores the proliferative capabilities of hepatocytes and renal proximal tubular cells. This growth response compensates cell loss due to uninhibited apoptosis and enables animal survival but rapidly leads to HCCs, renal cysts, and renal carcinomas. Thus, p21''s antiproliferative function is indispensable for the suppression of carcinogenesis from chronically injured liver and renal epithelial cells and cannot be compensated by apoptosis. [Copyright &y& Elsevier]

Abstract: Transgenic mice expressing the full-length HCV coding sequence were crossed with mice that express the HBV X gene-encoded regulatory protein HBx (ATX mice) to test the hypothesis that HBx expression accelerates HCV-induced liver pathogenesis. At 16 months (mo) of age, hepatocellular carcinoma was identified in 21% of HCV/ATX mice, but in none of the single transgenic animals. Analysis of 8-mo animals revealed that, relative to HCV/WT mice, HCV/ATX mice had more severe steatosis, greater liver-to-body weight ratios, and a significant increase in the percentage of hepatocytes staining for proliferating cell nuclear antigen. Furthermore, primary hepatocytes from HCV, ATX, and HCV/ATX transgenic mice were more resistant to fas-mediated apoptosis than hepatocytes from nontransgenic littermates. These results indicate that HBx expression contributes to increased liver pathogenesis in HCV transgenic mice by a mechanism that involves an imbalance in hepatocyte death and regeneration within the context of severe steatosis. [Copyright &y& Elsevier]

Objectives. Fatty liver is a common cause of liver disease in children. However, the epidemiology of pediatric fatty liver is limited to single-center case series of nonalcoholic fatty liver disease (NAFLD). Obesity and insulin resistance are major established risk factors for NAFLD. The role of gender, race, and ethnicity on the prevalence of fatty liver in obese children is unknown. Methods. We recruited obese 12th-grade participants from the Child and Adolescent Trial for Cardiovascular Health in California, Louisiana, Minnesota, and Texas. Serum samples were collected at school when the participants were well. Alanine aminotransferase (ALT) was measured by kinetic enzymatic assay, and ALT >40 U/L was defined as abnormal. Causes of abnormal ALT other than NAFLD were excluded by serum testing. Results. A total of 127 obese students (73 female, 54 male) had a mean BMI of 35.2 kg/m 2 . Unexplained ALT elevation was present in 23% of participants overall. The mean ALT for participants with normal values was 28 U/L and for participants with an abnormal ALT was 56 U/L. Abnormal ALT was significantly more prevalent in boys (44%) than in girls (7%). The prevalence of abnormal ALT differed significantly by race and ethnicity (Hispanic: 36%; white: 22%; black: 14%). Serum ALT value was significantly predicted by the combination of gender, race/ethnicity, and BMI. After controlling for gender and BMI, Hispanic ethnicity significantly predicted greater ALT than black race. Conclusions. In a national, school-based sample of obese adolescents, boys were 6 times more likely than girls to have an unexplained elevated ALT. Given that participants were well and causes of chronic liver disease were excluded, we speculate that obese adolescent boys have an increased prevalence of fatty liver compared with obese adolescent girls. This population-based study also supports the hypothesis that NAFLD is more common in Hispanic adolescents. These findings have implications for ... [ABSTRACT FROM AUTHOR]

AAV-8 is currently the most efficient serotype to transduce hepatocytes and establish long-lasting transgene expression. However, most vectors remain episomal, integration events are rare and occur randomly. In our study we aimed to prove that targeted integration and homologous recombination by AAV is a feasible method for gene correction in vivo. We therefore used the Fah5961SB mouse model carrying a single bp splice-site mutation causing loss of an exon in the fumarylacetoacetate hydrolase (Fah) gene. Fah mutant mice are a model of the human disease hereditary tyrosinemia type 1 and develop progressive liver failure when the protective drug NTBC is withdrawn. An AAV-8 vector was constructed containing 4.5 kb of the wild-type genomic sequence 5 and 3 of the splice mutation. Importantly, this vector does not contain a Fah expression cassette, but can restore Fah expression only after homologous recombination with the mutant genome. Neonatal (n=6, day of birth, 2x10^11 copies/mouse, intraperitoneal-ip), newborn (n=6, 4 days old, 1x10^11 copies/mouse, ip) and adult mice (n=8, 1x10^11 copies/mouse, portal vein) of both sexes were injected. Corrected hepatocytes were selected in vivo by NTBC withdrawal. Neonatal mice injected at the day of birth showed stabilization or increase of weight at the end of the first cycle of NTBC withdrawal (25 days). Multiple macroscopicallly visible nodules of healthy hepatic tissue were seen when the liver was harvested and histological analysis confirmed Fah+ nodules and thus gene correction at high frequency. Newborns injected at age 4 days and adult mice also showed flattening of weight loss after 25 days off NTBC. Histological analysis in these older mice also showed Fah-positive nodules providing evidence of correction of the point mutation. Further histological and genomic analysis to ascertain the precise quantity and time course of integration events are pending. Our experiments show for the first time in vivo that gene correction by homologous recombination with AAV-8 is possible at reasonable frequencies. Combined with in vivo selection this resulted in complete clinical restoration of an otherwise lethal metabolic liver disease.Molecular Therapy (2006) 13, S311–S312; doi: 10.1016/j.ymthe.2006.08.1225 [ABSTRACT FROM AUTHOR]