Hereditary Tyrosinemia Type Research Articles

Late Diagnosis of Hereditary Tyrosinemia Type I: The Case of Two First Cousins

Hereditary Tyrosinemia Type I (HT1) is a rare metabolic disorder caused by a deficiency in fumarylacetoacetate hydrolase, leading to the accumulation of toxic metabolites and resulting in hepatic and renal complications. This case report details a 10-year-old patient from a consanguineous family with a significant history of hepatic failure due to hepatocellular carcinoma. The patient presented with abdominal pain, jaundice, and urinary abnormalities, which led to the diagnosis of HT1, confirmed by elevated succinylacetone levels. Despite initial treatment with nitisinone and a low-protein diet, surgical resection of the hepatic mass was impeded by vascular invasion, necessitating preoperative chemotherapy. This case underscores the importance of early detection and a multidisciplinary approach in managing HT1, highlighting ongoing research into advanced therapies and genetic interventions to improve patient outcomes.

Mutation spectrum of Tyrosinemia type I in Iran, A retrospective cohort study

Hereditary Tyrosinemia Type 1 (HT1) is a genetic disorder characterized by an autosomal recessive inheritance pattern, caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene, which results in a deficiency of fumarylacetoacetase. In our study, we identified a total of 15 mutations, including 12 newly discovered and 3 previously reported pathogenic mutations, in a cohort of 19 Iranian patients with the acute form of HT1. Out of the 12 novel variants identified, 11 were missense variants: p.Asp126His, p.Gln75Glu, p.Leu385Pro, p.Ser92Thr, p.Leu96Arg, p.Val167Glu, p.Ala94Asp, p.Gly353Trp, p.Ser164Pro, p.Glu86His and p.Ala163Pro. Additionally, there was one nonsense variant, p.Try244X, that had not been previously reported. Interestingly, the Arg237X variant was found to be particularly prevalent in this study. Notably, three exons, namely exons 9, 3, and 6, exhibited a higher frequency of mutations. All of the identified variants are presumed to result in loss of function, impacting the clinical signs, disease progression, increasing tyrosine level, and the specific location of the mutation. Our study has provided valuable insights into the mutation spectrum of variants associated with HT1 disease which is reported for the first time from Iran. This information can facilitate the development of targeted mutation screening protocols, focusing on the most prevalent mutations within specific regions or ethnic groups.

Clinical, Biochemical, and Molecular Characteristics of Filipino Patients with Tyrosinemia Type 1.

Hereditary tyrosinemia type I (HT1), or hepatorenal tyrosinemia, is an amino acid disorder which may cause hepatic failure as well as renal and neurologic comorbidities. Early detection of this disorder is possible with newborn screening (NBS). The objective of this study is to describe the clinical, biochemical, and molecular characteristics of Filipino patients diagnosed with HT1 through the expansion of the Philippine NBS program in 2014. There were a total of 16 patients with confirmed HT1 from then until September 2022. Clinical and biochemical data during confirmation and initial evaluation, as well as molecular data, were obtained from the patients' medical records. The cohort included children between the ages of 18 and 54 months at the time of data collection. The mean age at treatment initiation was 26.8 days. The mean succinylacetone level from dried blood spot sampling using tandem mass spectrometry (MS) was 11.1 µmol/L. Biochemical confirmatory tests via plasma amino acid analysis showed mean levels of tyrosine, phenylalanine, and methionine of 506.1 µmol/L, 111.5 µmol/L, and 125.4 µmol/L, respectively. Upon urine organic acid (UOA) analysis, succinylacetone was detected in all except for one patient, who was managed prior to UOA analysis. The most common clinical characteristics were abnormal clotting times (62.5%), elevated alpha fetoprotein (37.5%), anemia (31.3%), and metabolic acidosis (31.3%). The most common genotype was homozygous c.122T>C p.Leu41Pro in 64.3% of patients. The allelic frequency of this pathogenic variant is 71.4%. The inclusion of HT1 in the Philippine NBS program allowed early diagnosis and management of HT1 patients.

In vivo dissection of the mouse tyrosine catabolic pathway with CRISPR-Cas9 identifies modifier genes affecting hereditary tyrosinemia type 1.

Hereditary tyrosinemia type 1 is an autosomal recessive disorder caused by mutations (pathogenic variants) in fumarylacetoacetate hydrolase, an enzyme involved in tyrosine degradation. Its loss results in the accumulation of toxic metabolites that mainly affect the liver and kidneys and can lead to severe liver disease and liver cancer. Tyrosinemia type 1 has a global prevalence of approximately 1 in 100,000 births but can reach up to 1 in 1,500 births in some regions of Québec, Canada. Mutating functionally related "modifier' genes (i.e. genes that, when mutated, affect the phenotypic impacts of mutations in other genes) is an emerging strategy for treating human genetic diseases. In vivo somatic genome editing in animal models of these diseases is a powerful means to identify modifier genes and fuel treatment development. In this study, we demonstrate that mutating additional enzymes in the tyrosine catabolic pathway through liver-specific genome editing can relieve or worsen the phenotypic severity of a murine model of tyrosinemia type 1. Neonatal gene delivery using recombinant adeno-associated viral vectors expressing Staphylococcus aureus Cas9 under the control of a liver-specific promoter led to efficient gene disruption and metabolic rewiring of the pathway, with systemic effects that were distinct from the phenotypes observed in whole-body knockout models. Our work illustrates the value of using in vivo genome editing in model organisms to study the direct effects of combining pathological mutations with modifier gene mutations in isogenic settings.

Improved specificity and efficacy of base-editing therapies with hybrid guide RNAs.

Phenylketonuria (PKU), hereditary tyrosinemia type 1 (HT1), and mucopolysaccharidosis type 1 (MPSI) are autosomal recessive disorders linked to the phenylalanine hydroxylase (PAH) gene, fumarylacetoacetate hydrolase (FAH) gene, and alpha-L-iduronidase (IDUA) gene, respectively. Potential therapeutic strategies to ameliorate disease include corrective editing of pathogenic variants in the PAH and IDUA genes and, as a variant-agnostic approach, inactivation of the 4-hydroxyphenylpyruvate dioxygenase (HPD) gene, a modifier of HT1, via adenine base editing. Here we evaluated the off-target editing profiles of therapeutic lead guide RNAs (gRNAs) that, when combined with adenine base editors correct the recurrent PAH P281L variant, PAH R408W variant, or IDUA W402X variant or disrupt the HPD gene in human hepatocytes. To mitigate off-target mutagenesis, we systematically screened hybrid gRNAs with DNA nucleotide substitutions. Comprehensive and variant-aware specificity profiling of these hybrid gRNAs reveal dramatically reduced off-target editing and reduced bystander editing. Lastly, in a humanized PAH P281L mouse model, we showed that when formulated in lipid nanoparticles (LNPs) with adenine base editor mRNA, selected hybrid gRNAs revert the PKU phenotype, substantially enhance on-target editing, and reduce bystander editing in vivo. These studies highlight the utility of hybrid gRNAs to improve the safety and efficacy of base-editing therapies.

Ex vivo gene editing and cell therapy for hereditary tyrosinemia type 1.

We previously demonstrated the successful use of in vivo CRISPR gene editing to delete 4-hydroxyphenylpyruvate dioxygenase (HPD) to rescue mice deficient in fumarylacetoacetate hydrolase (FAH), a disorder known as hereditary tyrosinemia type 1 (HT1). The aim of this study was to develop an ex vivo gene-editing protocol and apply it as a cell therapy for HT1. We isolated hepatocytes from wild-type (C57BL/6J) and Fah-/- mice and then used an optimized electroporation protocol to deliver Hpd-targeting CRISPR-Cas9 ribonucleoproteins into hepatocytes. Next, hepatocytes were transiently incubated in cytokine recovery media formulated to block apoptosis, followed by splenic injection into recipient Fah-/- mice. We observed robust engraftment and expansion of transplanted gene-edited hepatocytes from wild-type donors in the livers of recipient mice when transient incubation with our cytokine recovery media was used after electroporation and negligible engraftment without the media (mean: 46.8% and 0.83%, respectively; p=0.0025). Thus, the cytokine recovery medium was critical to our electroporation protocol. When hepatocytes from Fah-/- mice were used as donors for transplantation, we observed 35% and 28% engraftment for Hpd-Cas9 ribonucleoproteins and Cas9 mRNA, respectively. Tyrosine, phenylalanine, and biochemical markers of liver injury normalized in both Hpd-targeting Cas9 ribonucleoprotein and mRNA groups independent of induced inhibition of Hpd through nitisinone, indicating correction of disease indicators in Fah-/- mice. The successful liver cell therapy for HT1 validates our protocol and, despite the known growth advantage of HT1, showcases ex vivo gene editing using electroporation in combination with liver cell therapy to cure a disease model. These advancements underscore the potential impacts of electroporation combined with transplantation as a cell therapy.

Hepatobiliary circulation and dominant urinary excretion of homogentisic acid in a mouse model of alkaptonuria.

Altered activity of specific enzymes in phenylalanine-tyrosine (phe-tyr) metabolism results in incomplete breakdown of various metabolite substrates in this pathway. Increased biofluid concentration and tissue accumulation of the phe-tyr pathway metabolite homogentisic acid (HGA) is central to pathophysiology in the inherited disorder alkaptonuria (AKU). Accumulation of metabolites upstream of HGA, including tyrosine, occurs in patients on nitisinone, a licenced drug for AKU and hereditary tyrosinaemia type 1, which inhibits the enzyme responsible for HGA production. The aim of this study was to investigate the phe-tyr metabolite content of key biofluids and tissues in AKU mice on and off nitisinone to gain new insights into the biodistribution of metabolites in these altered metabolic states. The data show for the first time that HGA is present in bile in AKU (mean [±SD] = 1003[±410] μmol/L; nitisinone-treated AKU mean [±SD] = 45[±23] μmol/L). Biliary tyrosine, 3(4-hydroxyphenyl)pyruvic acid (HPPA) and 3(4-hydroxyphenyl)lactic acid (HPLA) are also increased on nitisinone. Urine was confirmed as the dominant elimination route of HGA in untreated AKU, but with indication of biliary excretion. These data provide new insights into pathways of phe-tyr metabolite biodistribution and metabolism, showing for the first time that hepatobiliary excretion contributes to the total pool of metabolites in this pathway. Our data suggest that biliary elimination of organic acids and other metabolites may play an underappreciated role in disorders of metabolism. We propose that our finding of approximately 3.8 times greater urinary HGA excretion in AKU mice compared with patients is one reason for the lack of extensive tissue ochronosis in the AKU mouse model.

Polymer-lipid nanoparticles enhance liver-targeted delivery of therapeutic base editor plasmid for the treatment of hereditary tyrosinemia type 1 (HT-1)

Polymer-lipid nanoparticles enhance liver-targeted delivery of therapeutic base editor plasmid for the treatment of hereditary tyrosinemia type 1 (HT-1)

Clinical Spectrum of Hereditary Tyrosinemia Type 1 in a Cohort of Pakistani Children.

Hereditary Tyrosinemia Type 1 (HT1), a rare autosomal recessive metabolic disorder, arises from fumarylacetoacetate (FAH) enzyme deficiency, resulting in toxic metabolite buildup. It manifests in acute, subacute, and chronic forms, with early diagnosis and Nitisinone treatment being vital. The study aims to highlight the different clinical presentations of Hereditary Tyrosinemia type 1 in a cohort of Pakistani children. Retrospective observational study. All patients diagnosed with HT1 at Shifa International Hospital, Islamabad and Pak Emirates Military Hospital, Rawalpindi between 2010 and 2023 were included. Information was collected regarding age, gender, symptoms, physical signs, and laboratory results. The study identified 6 cases of HT1. The average age at presentation was 8 months, with a mean delay in diagnosis of 26.8 months. Males were 4 (66.7%) and 2 (33.3%) were females. All patients had underlying liver disease presenting as abdominal distension with hepatosplenomegaly and accompanying growth failure. Four cases presented with rickets, 2 of which had hypophosphatemic rickets. Urine for succinylacetone was raised in all patients. Alpha fetoprotein was raised but hepatocellular carcinoma was diagnosed in 1 patient only. Low protein diet, and vitamin supplements were used for management. Five of the 6 patients died within 2 years of diagnosis. Delayed referrals and unavailability of Nitisinone are the major challenges in diagnosing and treating HT1 in Pakistan.

Electronic structure and molecular properties of nitisinone and mesotrione in water

ContextNitisinone is a medium-sized organic molecule that is used in treating hereditary tyrosinemia type 1 (HT-1). The structurally analogous mesotrione, however, is used as a pesticide/herbicide. What molecular properties are responsible for the similarity/dissimilarity of these molecules is investigated here. The solvent effect reduces the electron affinity to rather negative values and causes the negative electron affinity which manifests itself in a very high positive absolute reduction potential.MethodsB3LYP method was utilized for a geometry optimization of nitisinone and mesotrione in their neural and ionized (L0, L+, L−) forms of 6 structures. The calculations were conducted in water as a solvent using conductor-like polarizable continuum model (CPCM), nitisinone also in vacuo. The complete vibrational analysis at the true energy minimum allows evaluating the thermodynamic functions with focus to the zero-point energy and overall entropic term. The change of the Gibbs energy on reductions and/or oxidation facilitates evaluating the absolute reduction and absolute oxidation potentials. Also, DLPNO-CCSD(T) method that involves the major part of the correlation energy has been applied to nitisinone and mesotrione and their molecular ions.

An engineered Escherichia coli Nissle strain prevents lethal liver injury in a mouse model of tyrosinemia type 1

Hereditary tyrosinemia type 1 (HT1) results from the loss of fumarylacetoacetate hydrolase (FAH) activity and can lead to lethal liver injury. Therapeutic options for HT1 remain limited. In this study, we aimed to construct an engineered bacterium capable of reprogramming host metabolism and thereby provide a potential alternative approach for the treatment of HT1. Escherichia coli Nissle 1917 (EcN) was engineered to express genes involved in tyrosine metabolism in the anoxic conditions that are characteristic of the intestine (EcN-HT). Bodyweight, survival rate, plasma (tyrosine/liver function), H&E staining and RNA sequencing were used to assess its ability to degrade tyrosine and protect against lethal liver injury in Fah-knockout (KO) mice, a well-accepted model of HT1. EcN-HT consumed tyrosine and produced L-DOPA (levodopa) in an invitro system. Importantly, in Fah-KO mice, the oral administration of EcN-HT enhanced tyrosine degradation, reduced the accumulation of toxic metabolites, and protected against lethal liver injury. RNA sequencing analysis revealed that EcN-HT rescued the global gene expression pattern in the livers of Fah-KO mice, particularly of genes involved in metabolic signaling and liver homeostasis. Moreover, EcN-HT treatment was found to be safe and well-tolerated in the mouse intestine. This is the first report of an engineered live bacterium that can degrade tyrosine and alleviate lethal liver injury in mice with HT1. EcN-HT represents a novel engineered probiotic with the potential to treat this condition. Patients with hereditary tyrosinemia type 1 (HT1) are characterized by an inability to metabolize tyrosine normally and suffer from liver failure, renal dysfunction, neurological impairments, and cancer. Given the overlap and complementarity between the host and microbial metabolic pathways, the gut microbiome provides a potential chance to regulate host metabolism through degradation of tyrosine and reduction of byproducts that might be toxic. Herein, we demonstrated that an engineered live bacterium, EcN-HT, could enhance tyrosine breakdown, reduce the accumulation of toxic tyrosine byproducts, and protect against lethal liver injury in Fah-knockout mice. These findings suggested that engineered live biotherapeutics that can degrade tyrosine in the gut may represent a viable and safe strategy for the prevention of lethal liver injury in HT1 as well as the mitigation of its associated pathologies.

Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype

Hereditary tyrosinemia type 1 (HT1) is a genetic disorder of the tyrosine degradation pathway (TIMD) with unmet therapeutic needs. HT1 patients are unable to fully break down the amino acid tyrosine due to a deficient fumarylacetoacetate hydrolase (FAH) enzyme and, therefore, accumulate toxic tyrosine intermediates. If left untreated, they experience hepatic failure with comorbidities involving the renal and neurological system and the development of hepatocellular carcinoma (HCC). Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death. However, despite its demonstrated benefits, HT1 patients under continuous NTBC therapy are at risk to develop HCC and adverse reactions in the eye, blood and lymphatic system, the mechanism of which is poorly understood. Moreover, NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1. Here, the changes in molecular pathways associated to the development and progression of HT1-driven liver disease that remains uncorrected under NTBC therapy were investigated using whole transcriptome analyses on the livers of Fah- and Hgd-deficient mice under continuous NTBC therapy and after seven days of NTBC therapy discontinuation. Alkaptonuria (AKU) was used as a tyrosine-inherited metabolic disorder reference disease with non-hepatic manifestations. The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC. Most importantly, a set of 25 genes related to liver disease and HCC development was identified that was differentially regulated in HT1 vs. AKU mouse livers under NTBC therapy. Some of those were further modulated upon NTBC therapy discontinuation in HT1 but not in AKU livers. Altogether, our data indicate that NTBC therapy does not completely resolves HT1-driven liver disease and supports the sustained risk to develop HCC over time as different HCC markers, including Moxd1, Saa, Mt, Dbp and Cxcl1, were significantly increased under NTBC.

A patient with urinary succinylacetone-negative hereditary tyrosinemia type 1.

A patient with urinary succinylacetone-negative hereditary tyrosinemia type 1.

Short-term nitisinone discontinuation of hereditary tyrosinemia type 1 mice causes metabolic alterations in glutathione metabolism/biosynthesis and multiple amino acid degradation pathways

Short-term nitisinone discontinuation of hereditary tyrosinemia type 1 mice causes metabolic alterations in glutathione metabolism/biosynthesis and multiple amino acid degradation pathways

The compound heterozygous mutations of c.607G>a and c.657delC in the FAH gene are associated with renal damage with hereditary tyrosinemia type 1 (HT1).

Hereditary tyrosinemia type 1 (HT1) is a rare inherited metabolic disease characterized by severe liver and renal dysfunction. Early identification in affected children is critical for improved treatment options and prognosis. In this study, we identified novel compound heterozygous mutations (NM_000137: c.657delC (p.K220Rfs*12) and c.607G>A (p.A203T)) in the fumarylacetoacetate hydrolase (FAH) gene in a family. We also characterized the clinical phenotype of the proband and verified the pathogenic effects of the mutations. Furthermore, we explored the pathogenic mechanism of renal injury through renal biopsy pathology and cell-based in vitro assays. Our study aims to verify the association between novel fumarylacetoacetate hydrolase (FAH) variants and HT1, confirm the pathogenic effects of the mutations and explore the pathogenic mechanism of renal injury. We showed these FAH mutations were inherited in an autosomal recessive manner and resulted in abnormal FAH protein expression and dysfunction, leading to fumarylacetoacetate (FAA) accumulation. The proband also showed apparent renal injury, including glomerular filtration barrier dysfunction and abnormal tubular protein reabsorption. These observations may provide deeper insights on disease pathogenesis and identify potential therapeutic approaches for HT1 from a genetic perspective. Similarly, we hope to provide valuable information for genetic counseling and prenatal diagnostics.

Initial presentation, management and follow-up data of 33 treated patients with hereditary tyrosinemia type 1 in the absence of newborn screening

Hereditary tyrosinemia type 1 (HT1) is a rare autosomal recessive disorder of phenylalanine and tyrosine catabolism due to a deficiency of fumarylacetoacetate hydrolase. HT1 has a large clinical spectrum with acute forms presenting before six months of age, subacute forms with initial symptoms occurring between age 6 and 12 months, and chronic forms after 12 months of age. Without treatment, HT1 results in the accumulation of toxic metabolites leading to liver disease, proximal tubular dysfunction, and porphyria-like neurological crises. Since the early nineties, the outcome of HT1 has dramatically changed due to its treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC, nitisinone). In some countries, HT1 is included in the newborn screening program based on the analysis of succinylacetone concentration on dried blood spots.In the present study, we report clinical and laboratory parameters data on 33 HT1 patients focusing on clinical presentation and therapeutic management at the time of diagnosis. Eighteen patients were diagnosed with the acute form (median age at presentation 2.5 months), 6 with the subacute form (median age at presentation 10 months), and 5 with the chronic form of HT1 (median age at presentation 15 months). Four patients were diagnosed pre-symptomatically in the setting of a family history of HT1. Among the 29 symptomatic patients, hepatomegaly was found in 83% of patients and prolonged coagulation times due to hepatocellular insufficiency was observed in 93% of patients. HT1 diagnosis was confirmed by increased urine succinylacetone in all patients. All patients but 2 were treated with nitisinone immediately at diagnosis. During follow-up, 2 patients received liver transplant for high grade dysplasia or hepatocellular carcinoma, 10 patients exhibited some form of neurocognitive impairments.Our data confirm that HT1 is a severe treatable liver disease that should be detected at the earliest, ideally by newborn screening and appropriately treated.

Activation of homology-directed DNA repair plays key role in CRISPR-mediated genome correction.

Gene editing for the cure of inborn errors of metabolism (IEMs) has been limited by inefficiency of adult hepatocyte targeting. Here, we demonstrate that in utero CRISPR/Cas9-mediated gene editing in a mouse model of hereditary tyrosinemia type 1 provides stable cure of the disease. Following this, we performed an extensive gene expression analysis to explore the inherent characteristics of fetal/neonatal hepatocytes that make them more susceptible to efficient gene editing than adult hepatocytes. We showed that fetal and neonatal livers are comprised of proliferative hepatocytes with abundant expression of genes involved in homology-directed repair (HDR) of DNA double-strand breaks (DSBs), key for efficient gene editing by CRISPR/Cas9. We demonstrated the same is true of hepatocytes after undergoing a regenerative stimulus (partial hepatectomy), where post-hepatectomy cells show a higher efficiency of HDR and correction. Specifically, we demonstrated that HDR-related genome correction is most effective in the replicative phase, or S-phase, of an actively proliferating cell. In conclusion, this study shows that taking advantage of or triggering cell proliferation, specifically DNA replication in S-phase, may serve as an important tool to improve efficiency of CRISPR/Cas9-mediated genome editing in the liver and provide a curative therapy for IEMs in both children and adults.

In vivo quantitative photoacoustic evaluation of the liver and kidney pathology in tyrosinemia

Hereditary tyrosinemia type Ⅰ (HT1) is a severe autosomal recessive inherited metabolic disease, which can result in severe damage of liver and kidney. Photoacoustic imaging (PAI) uses pulsed laser light to induce ultrasonic signals to facilitate the visualization of lesions that are strongly related to disease progression. In this study, the structural and functional changes of liver and kidney in HT1 was investigated by cross-scale PAI. The results showed that the hepatic lobule and renal tubule were severely damaged during HT1 progression. The hemoglobin content, vessel density, and liver function reserve were decreased. The metabolic half-life of indocyanine green declined from 59.8 s in health to 262.6 s in the advanced stage. Blood oxygen saturation was much lower than that in health. This study highlights the potential of PAI for in vivo evaluation of the liver and kidney lesions in HT1.

The Discovery of the Mode of Action of Nitisinone.

This review briefly discusses the discovery of the mode of action of the triketone herbicide, 2-(2-nitro-4-trifluormethylbenzoyl)-1,3-cyclohexanedione and its use as a drug Nitisinone for the treatment of inborn errors of tyrosine metabolism. Nitisinone is a potent reversible tight-binding inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase, involved in the catabolism of the amino acid tyrosine. Nitisinone is used to treat the rare disease hereditary tyrosinaemia type 1 where the last enzyme in the breakdown of tyrosine, fumarylacetoacetase is deficient. Nitisinone is also used to treat patients with alkaptonuria where the enzyme homogentisic acid oxidase is deficient. Articles in this issue discuss metabolites of tyrosine catabolism in healthy patients and those with alkaptonuria.

In vivo lentiviral vector gene therapy to cure hereditary tyrosinemia type 1 and prevent development of precancerous and cancerous lesions

Conventional therapy for hereditary tyrosinemia type-1 (HT1) with 2-(2-nitro-4-trifluoromethylbenzoyl)−1,3-cyclohexanedione (NTBC) delays and in some cases fails to prevent disease progression to liver fibrosis, liver failure, and activation of tumorigenic pathways. Here we demonstrate cure of HT1 by direct, in vivo administration of a therapeutic lentiviral vector targeting the expression of a human fumarylacetoacetate hydrolase (FAH) transgene in the porcine model of HT1. This therapy is well tolerated and provides stable long-term expression of FAH in pigs with HT1. Genomic integration displays a benign profile, with subsequent fibrosis and tumorigenicity gene expression patterns similar to wild-type animals as compared to NTBC-treated or diseased untreated animals. Indeed, the phenotypic and genomic data following in vivo lentiviral vector administration demonstrate comparative superiority over other therapies including ex vivo cell therapy and therefore support clinical application of this approach.