Monogenic diseases that can be cured by liver transplantation

Human liver organoids: From generation to applications

In the last decade, research into human hepatology has been revolutionized by the development of mini human livers in a dish. These liver organoids are formed by self-organizing stem cells and resemble their native counterparts in cellular content, multicellular architecture, and functional features. Liver organoids can be derived from the liver tissue or pluripotent stem cells generated from a skin biopsy, blood cells, or renal epithelial cells present in urine. With the development of liver organoids, a large part of previous hurdles in modeling the human liver is likely to be solved, enabling possibilities to better model liver disease, improve (personalized) drug testing, and advance bioengineering options. In this review, we address strategies to generate and use organoids in human liver disease modeling, followed by a discussion of their potential application in drug development and therapeutics, as well as their strengths and limitations.

Research progress and application of liver organoids for disease modeling and regenerative therapy

The liver is a major metabolic organ of the human body and has a high incidence of diseases. In recent years, the annual incidence of liver disease has increased, seriously endangering human life and health. The study of the occurrence and development mechanism of liver diseases, discovery of new therapeutic targets, and establishment of new methods of medical treatment are major issues related to the national economy and people's livelihood. The development of stable and effective research models is expected to provide new insights into the pathogenesis of liver diseases and the search for more effective treatment options. Organoid technology is a new in vitro culture system, and organoids constructed by human cells can simulate the morphological structure, gene expression, and glucose and lipid metabolism of organs in vivo, providing a new model for related research on liver diseases. This paper reviews the latest research progress on liver organoids from the establishment of cell sources and application of liver organoids and discusses their application potential in the field of liver disease research.

Lipid nanoparticles as the drug carrier for targeted therapy of hepatic disorders

The liver, a complex and vital organ in the human body, is susceptible to various diseases, including metabolic disorders, acute hepatitis, cirrhosis, and hepatocellular carcinoma. In recent decades, these diseases have significantly contributed to global morbidity and mortality. Currently, liver transplantation remains the most effective treatment for hepatic disorders. Nucleic acid therapeutics offer a selective approach to disease treatment through diverse mechanisms, enabling the regulation of relevant genes and providing a novel therapeutic avenue for hepatic disorders. It is expected that nucleic acid drugs will emerge as the third generation of pharmaceuticals, succeeding small molecule drugs and antibody drugs. Lipid nanoparticles (LNPs) represent a crucial technology in the field of drug delivery and constitute a significant advancement in gene therapies. Nucleic acids encapsulated in LNPs are shielded from the degradation of enzymes and effectively delivered to cells, where they are released and regulate specific genes. This paper provides a comprehensive review of the structure, composition, and applications of LNPs in the treatment of hepatic disorders and offers insights into prospects and challenges in the future development of LNPs.

Engineered exosomes in emerging cell-free therapy

The discovery and use of exosomes ushered in a new era of cell-free therapy. Exosomes are a subgroup of extracellular vesicles that show great potential in disease treatment. Engineered exosomes. with their improved functions have attracted intense interests of their application in translational medicine research. However, the technology of engineering exosomes still faces many challenges which have been the great limitation for their clinical application. This review summarizes the current status of research on engineered exosomes and the difficulties encountered in recent years, with a view to providing new approaches and ideas for future exosome modification and new drug development.

Domino liver transplantation for maple syrup urine disease in children: A single-center case series

BACKGROUND

Domino liver transplant (DLT) represents another type of liver donor to expand the donor pool. Recent reports of successful DLT in children with maple syrup urine disease (MSUD) show promising long-term outcomes.

METHODS

It was a retrospective study. All children with MSUD were paired with either recipients with end-stage liver disease (ESLD) or non-MSUD metabolic disease. Each pair underwent simultaneous liver transplant (LT), where the MSUD recipient received the graft from a living-related donor and the liver explanted from the MSUD donor was transplanted to the respective paired domino recipient. We report our experience regarding the techniques and outcomes of DLT at our center.

RESULTS

Eleven children with MSUD and 12 respective DLT recipients were enrolled, one of which was domino split-liver transplantation. DLT recipients included seven ESLD, two propionic acidemia (PA), one glycogen storage disease(GSD) type-1, one GSD type-3, and one Citrullinemia. Post-LT ICU and hospital stays were comparable (p > .05). Patient and graft survival was 100% and 66.6% in the MSUD group and DLT recipients at a mean follow-up of 13.5 and 15 months. There was no death in the MSUD group as compared to four in the DLT group. The amino acid levels rapidly normalized after the LT in the children with MSUD and they tolerated the normal unrestricted diet. No vascular, biliary, or graft-related complications were seen in the post-transplant period. No occurrence of MSUD was noted in DLT recipients.

CONCLUSION

DLTs have excellent post-surgical outcomes. DLT should be strongly considered and adopted by transplant programs worldwide to circumvent organ shortage.

Relevance of next generation sequencing (NGS) data re-analysis in the diagnosis of monogenic diseases leading to organ failure

BACKGROUND

In 2018, our center started a program to offer genetic diagnosis to patients with kidney and liver monogenic rare conditions, potentially eligible for organ transplantation. We exploited a clinical exome sequencing approach, followed by analyses of in silico gene panels tailored to clinical suspicions, obtaining detection rates in line with what reported in literature. However, a percentage of patients remains without a definitive genetic diagnosis. This work aims to evaluate the utility of NGS data re-analysis for those patients with an inconclusive or negative genetic test at the time of first analysis considering that (i) the advance of alignment and variant calling processes progressively improve the detection rate, limiting false positives and false negatives; (ii) gene panels are periodically updated and (iii) variant annotation may change over time.

METHODS

114 patients, recruited between 2018 and 2020, with an inconclusive or negative NGS report at the time of first analysis, were included in the study. Re-alignment and variant calling of previously generated sequencing raw data were performed using the GenomSys Variant Analyzer software.

RESULTS

21 previously not reported potentially causative variants were identified in 20 patients. In most cases (n = 19), causal variants were retrieved out of the re-classification from likely benign to variants of unknown significance (VUS). In one case, the variant was included because of inclusion in the analysis of a newly disease-associated gene, not present in the original gene panel, and in another one due to the improved data alignment process. Whenever possible, variants were validated with Sanger sequencing and family segregation studies. As of now, 16 out of 20 patients have been analyzed and variants confirmed in 8 patients. Specifically, in two pediatric patients, causative variants were de novo mutations while in the others, the variant was present also in other affected relatives. In the remaining patients, variants were present also in non-affected parents, raising questions on their re-classification.

CONCLUSIONS

Overall, these data indicate that periodic and systematic re-analysis of negative or inconclusive NGS data reports can lead to new variant identification or reclassification in a small but significant proportion of cases, with benefits for patients' management.

Genome editing without nucleases confers proliferative advantage to edited hepatocytes and corrects Wilson disease

Application of classic liver-directed gene replacement strategies is limited in genetic diseases characterized by liver injury due to hepatocyte proliferation, resulting in decline of therapeutic transgene expression and potential genotoxic risk. Wilson disease (WD) is a life-threatening autosomal disorder of copper homeostasis caused by pathogenic variants in copper transporter ATP7B and characterized by toxic copper accumulation, resulting in severe liver and brain diseases. Genome editing holds promise for the treatment of WD; nevertheless, to rescue copper homeostasis, ATP7B function must be restored in at least 25% of the hepatocytes, which surpasses by far genome-editing correction rates. We applied a liver-directed, nuclease-free genome editing approach, based on adeno-associated viral vector-mediated (AAV-mediated) targeted integration of a promoterless mini-ATP7B cDNA into the albumin (Alb) locus. Administration of AAV-Alb-mini-ATP7B in 2 WD mouse models resulted in extensive liver repopulation by genome-edited hepatocytes holding a proliferative advantage over nonedited ones, and ameliorated liver injury and copper metabolism. Furthermore, combination of genome editing with a copper chelator, currently used for WD treatment, achieved greater disease improvement compared with chelation therapy alone. Nuclease-free genome editing provided therapeutic efficacy and may represent a safer and longer-lasting alternative to classic gene replacement strategies for WD.

Gene Therapy in Patients with the Crigler-Najjar Syndrome

BACKGROUND

Patients with the Crigler-Najjar syndrome lack the enzyme uridine diphosphoglucuronate glucuronosyltransferase 1A1 (UGT1A1), the absence of which leads to severe unconjugated hyperbilirubinemia that can cause irreversible neurologic injury and death. Prolonged, daily phototherapy partially controls the jaundice, but the only definitive cure is liver transplantation.

METHODS

We report the results of the dose-escalation portion of a phase 1-2 study evaluating the safety and efficacy of a single intravenous infusion of an adeno-associated virus serotype 8 vector encoding UGT1A1 in patients with the Crigler-Najjar syndrome that was being treated with phototherapy. Five patients received a single infusion of the gene construct (GNT0003): two received 2×1012 vector genomes (vg) per kilogram of body weight, and three received 5×1012 vg per kilogram. The primary end points were measures of safety and efficacy; efficacy was defined as a serum bilirubin level of 300 μmol per liter or lower measured at 17 weeks, 1 week after discontinuation of phototherapy.

RESULTS

No serious adverse events were reported. The most common adverse events were headache and alterations in liver-enzyme levels. Alanine aminotransferase increased to levels above the upper limit of the normal range in four patients, a finding potentially related to an immune response against the infused vector; these patients were treated with a course of glucocorticoids. By week 16, serum bilirubin levels in patients who received the lower dose of GNT0003 exceeded 300 μmol per liter. The patients who received the higher dose had bilirubin levels below 300 μmol per liter in the absence of phototherapy at the end of follow-up (mean [±SD] baseline bilirubin level, 351±56 μmol per liter; mean level at the final follow-up visit [week 78 in two patients and week 80 in the other], 149±33 μmol per liter).

CONCLUSIONS

No serious adverse events were reported in patients treated with the gene-therapy vector GNT0003 in this small study. Patients who received the higher dose had a decrease in bilirubin levels and were not receiving phototherapy at least 78 weeks after vector administration. (Funded by Genethon and others; ClinicalTrials.gov number, NCT03466463.).

Effect of liver transplantation with primary hyperoxaluria type 1: Five case reports and review of literature

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease stemming from a deficiency in liver-specific alanine-glyoxylate aminotransferase, resulting in increased endogenous oxalate deposition and end-stage renal disease. Organ transplantation is the only effective treatment. However, its approach and timing remain controversial.

CASE SUMMARY

We retrospectively analyzed 5 patients diagnosed with PH1 from the Liver Transplant Center of the Beijing Friendship Hospital from March 2017 to December 2020. Our cohort included 4 males and 1 female. The median age at onset was 4.0 years (range: 1.0-5.0), age at diagnosis was 12.2 years (range: 6.7-23.5), age at liver transplantation (LT) was 12.2 years (range: 7.0-25.1), and the follow-up time was 26.3 mo (range: 12.8-40.1). All patients had delayed diagnosis, and 3 patients had progressed to end-stage renal disease by the time they were diagnosed. Two patients received preemptive LT; their estimated glomerular filtration rate was maintained at > 120 mL/min/1.73 m², indicating a better prognosis. Three patients received sequential liver and kidney transplantation. After transplantation, serum and urinary oxalate decreased, and liver function recovered. At the last follow-up, the estimated glomerular filtration rates of the latter 3 patients were 179, 52 and 21 mL/min/1.73 m².

CONCLUSION

Different transplantation strategies should be adopted for patients based on their renal function stage. Preemptive-LT offers a good therapeutic approach for PH1.

Microbiota-Liver Diseases Interactions

Gut microbiota regulates essential processes of host metabolism and physiology: synthesis of vitamins, digestion of foods non-digestible by the host (such as fibers), and-most important-protects the digestive tract from pathogens. In this study, we focus on the CRISPR/Cas9 technology, which is extensively used to correct multiple diseases, including liver diseases. Then, we discuss the non-alcoholic fatty liver disease (NAFLD), affecting more than 25% of the global population; colorectal cancer (CRC) is second in mortality. We give space to rarely discussed topics, such as pathobionts and multiple mutations. Pathobionts help to understand the origin and complexity of the microbiota. Since several types of cancers have as target the gut, it is vital extending the research of multiple mutations to the type of cancers affecting the gut-liver axis.

Genome editing-mediated knock-in of therapeutic genes ameliorates the disease phenotype in a model of hemophilia

Recently, clinical trials of adeno-associated virus-mediated replacement therapy have suggested long-term therapeutic effects for several genetic diseases of the liver, including hemophilia. However, there remain concerns regarding decreased therapeutic effects when the liver is regenerated or when physiological proliferation occurs. Although genome editing using the clustered regularly interspaced short palindromic repeats/Cas9 system provides an opportunity to solve this problem, low knock-in efficiency may limit its application for therapeutically relevant expression. Here, we identified a novel gene, APOC3, in which a strong promoter facilitated the expression of knocked-in genes in hepatocytes. We also investigated the effects of APOC3 editing using a small Cas9 protein derived from Campylobacter jejuni (CjCas9) in a hemophilic model. We demonstrated that adeno-associated virus-mediated delivery of CjCas9 and donor led to moderate levels of human factor 9 expression in APOC3-humanized mice. Moreover, knock-in-driven expression induced substantial recovery of clotting function in mice with hemophilia B. There was no evidence of off-target editing in vitro or in vivo. Collectively, our findings demonstrated therapeutically relevant expression using a precise and efficient APOC3-editing platform, providing insights into the development of further long-term therapeutics for diverse monogenic liver diseases.

Full-length ATP7B reconstituted through protein trans-splicing corrects Wilson disease in mice

Wilson disease (WD) is a genetic disorder of copper homeostasis, caused by deficiency of the copper transporter ATP7B. Gene therapy with recombinant adeno-associated vectors (AAV) holds promises for WD treatment. However, the full-length human ATP7B gene exceeds the limited AAV cargo capacity, hampering the applicability of AAV in this disease context. To overcome this limitation, we designed a dual AAV vector approach using split intein technology. Split inteins catalyze seamless ligation of two separate polypeptides in a highly specific manner. We selected a DnaE intein from Nostoc punctiforme (Npu) that recognizes a specific tripeptide in the human ATP7B coding sequence. We generated two AAVs expressing either the 5′-half of a codon-optimized human ATP7B cDNA followed by the N-terminal Npu DnaE intein or the C-terminal Npu DnaE intein followed by the 3′-half of ATP7B cDNA, under the control of a liver-specific promoter. Intravenous co-injection of the two vectors in wild-type and Atp7b^−/− mice resulted in efficient reconstitution of full-length ATP7B protein in the liver. Moreover, Atp7b^−/− mice treated with intein-ATP7B vectors were protected from liver damage and showed improvements in copper homeostasis. Taken together, these data demonstrate the efficacy of split intein technology to drive the reconstitution of full-length human ATP7B and to rescue copper-mediated liver damage in Atp7b^−/− mice, paving the way to the development of a new gene therapy approach for WD.

Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice

Maple syrup urine disease (MSUD) is a rare recessively inherited metabolic disorder causing accumulation of branched chain amino acids leading to neonatal death, if untreated. Treatment for MSUD represents an unmet need because the current treatment with life-long low-protein diet is challenging to maintain, and despite treatment the risk of acute decompensations and neuropsychiatric symptoms remains. Here, based on significant liver contribution to the catabolism of the branched chain amino acid leucine, we develop a liver-directed adeno-associated virus (AAV8) gene therapy for MSUD. We establish and characterize the Bckdha (branched chain keto acid dehydrogenase a)^−/− mouse that exhibits a lethal neonatal phenotype mimicking human MSUD. Animals were treated at P0 with intravenous human BCKDHA AAV8 vectors under the control of either a ubiquitous or a liver-specific promoter. BCKDHA gene transfer rescued the lethal phenotype. While the use of a ubiquitous promoter fully and sustainably rescued the disease (long-term survival, normal phenotype and correction of biochemical abnormalities), liver-specific expression of BCKDHA led to partial, though sustained rescue. Here we show efficacy of gene therapy for MSUD demonstrating its potential for clinical translation.

Maple syrup urine disease (MSUD) is a rare inborn error of metabolism, which is currently treated with life-long low-protein diet that can be challenging to maintain. Here the authors develop an AAV8-directed gene therapy providing sustainable disease rescue in a mouse model of MSUD.

The utility of hierarchical genetic testing in paediatric liver disease

BACKGROUND & AIMS

Genetic factors underlie a substantial proportion of paediatric liver diseases. Hereditary liver diseases have considerable genetic heterogeneity and variable clinical manifestations, which bring great challenges to clinical and molecular diagnoses. In this study, we investigated a group of paediatric patients with varying degrees of liver dysfunction using a hierarchical genetic testing strategy.

METHODS

We first applied a panel encompassing 166 known causal genes of liver disease. We then used exome sequencing (ES) in those patients whose cases remained undiagnosed to identify the genetic aetiology of their symptoms.

RESULTS

In total, we enrolled 131 unrelated paediatric patients with liver disease of Chinese Han ethnicity. We first applied targeted gene sequencing of 166 genes to all patients and yielded a diagnostic rate of 35.9% (47 of 131). Eighty-four patients who remained undiagnosed after target gene sequencing were subjected to ES. As a result, eight (8/84, 9.5%) of them obtained molecular diagnoses, including four patients suspected of abnormal bilirubin metabolism and four idiopathic cases. Non-typical genetic findings, including digenic inheritance and dual molecular diagnosis, were also identified. Through a comprehensive assessment of novel candidate variants of uncertain disease association, 11 patients of the remaining undiagnosed patients were able to obtain likely molecular diagnoses.

CONCLUSIONS

Our study presents evidence for the diagnostic utility of sequential genetic testing in a cohort of patients with paediatric liver disease. Our findings expand the understanding of the phenotypic and mutational spectrum underlying this heterogeneous group of diseases.

Liver Transplantation: A Safe and Definitive Alternative to Lifelong Nitisinone for Tyrosinemia Type 1

OBJECTIVES

To report the experience of liver transplantation (LT) for tyrosinemia type 1 (TT-1).

METHODS

Clinical data of children with TT-1 who underwent living donor LT between July 2009 and May 2020 were retrospectively analyzed. Data included pre-LT nitisinone therapy, graft type, post-LT complications, HCC incidence, and graft/patient survival.

RESULTS

Nine children were diagnosed with TT-1 at a median age of 12 mo (6-54 mo). Nitisinone was started in 6 patients at a median age of 15 mo (6-42 mo), but all had frequent interruption of therapy due to logistics with drug procurement including its cost. Median age at transplantation was 5 y (2-11 y). Explant liver showed HCC in 5 patients (55% of total cohort). The graft and patient survival are 100% with median follow-up of 58 mo (24-84 mo).

CONCLUSION

LT is curative for TT-1 and excellent results can be obtained in experienced centers. This is especially favorable in countries with limited resources where the cost of medical therapy is highly prohibitive, with lifelong diet restrictions and unclear long-term risk of HCC.

Dexamethasone Transiently Enhances Transgene Expression in the Liver When Administered at Late-Phase Post Long-Term Adeno-Associated Virus Transduction

Glucocorticoids have anti-inflammatory and immunosuppressive functions and have commonly been used for preventing liver toxicity after the systemic application of a high dose of adeno-associated virus (AAV) vector for gene therapy. Clinical studies have reported that glucocorticoids have rescued factor IX (FIX) expression in patients with hemophilia B who showed a reduced FIX expression at 6 to 10 weeks post-AAV vector administration. In this study, we explored whether glucocorticoids could affect transgene expression in AAV targeted livers in animal models. When dexamethasone was applied before AAV9/FIX vector administration in the wild-type C57BL/6 mice, FIX expression was much higher than that of the control mice at any time point. More importantly, FIX expression transiently increased after dexamethasone was administered at week 6 or later post-AAV injection regardless of the various dexamethasone treatments applied. The transient enhancement in transgene expression was observed once there were one to several consecutive dexamethasone treatments completed. A similar result was also achieved in other wild-type BALB/c and hemophilia B mice that were treated with AAV9/FIX and dexamethasone. This mechanism study demonstrated that the administration of dexamethasone did not change either AAV genome copy number or transgene expression at the transcription level but transiently decreased interferon beta (IFN-β) and tumor necrosis factor alpha (TNF-α) expression in the livers of mice at a later time after AAV injection. Next, we studied the effect of dexamethasone on late transgene expression in hemophilia B dogs. Dexamethasone was administered 1 year after AAV9/FIX injection. Inconsistent with the results in mice, no significant change of FIX expression was observed in hemophilia B dogs. In summary, the results from this study indicate that dexamethasone may have various effects on transgene expression in AAV-transduced livers in different species, which provides valuable information about the rational application of dexamethasone in future clinical studies.

Preparation and Characterization of a Liver Targeted, Poly(amidoamine) Based, Gene Delivery System

Nonalcoholic steatohepatitis (NASH) is an aggressive liver disease that is considered a major cause of liver cirrhosis and hepatocellular carcinoma. NASH is characterized by multiple underlying genetic mutations, with no approved cure to date. Gene therapies that target those genetic mutations may play a major role in treating this disease, once delivered specifically to the hepatocytes. In this chapter we present, in detail, the synthesis and the characterization of an efficient gene delivery system capable of targeting hepatocytes by exploiting the overexpression of asialoglycoprotein receptors on their cell surface. The targeting ligand, galactose derivative, lactobionic acid (Gal), is first conjugated to bifunctional poly(ethylene glycol) (PEG), and then the formed PEG-Gal is further conjugated to the positively charged polymer, poly(amidoamine) (PAMAM) to form a PAMAM-PEG-Gal construct that can complex and deliver genetic material (e.g., pDNA, siRNA, mRNA) specifically to hepatocytes. We first synthesize PAMAM-PEG-Gal using carbodiimide click chemistry. The synthesized conjugate is characterized using ¹H NMR spectroscopy and mass spectrometry. Next, nanoplexes are prepared by combining the positively charged conjugate and the negatively charged genetic material at different nitrogen to phosphate (N/P) ratios; then the size, charge, electrophoretic mobility, and surface morphology of those nanoplexes are estimated. The simplicity of complexing our conjugate with any type of genetic material, the ability of our delivery system to overcome the current limitations of delivering naked genetic material, and the efficiency of delivering its payload specifically to hepatocytes, makes our formulation a promising tool to treat any type of genetic abnormality that arises in hepatocytes, and specifically NASH.

Auxiliary Liver Graft Can Be Protected From HBV Infection in HBsAg Positive Blood Circulation

Auxiliary grafts have a high risk of Hepatitis B virus (HBV) infection in patients with chronic HBV-related diseases. Hepatitis B virus-related auxiliary partial orthotopic liver transplantation (APOLT) cases were reviewed to show the results of current methods to block native-to-graft HBV transmission. Three patients received APOLT for HBV-related liver cirrhosis and a recurrent upper gastrointestinal hemorrhage between April 2015 and January 2017 by the liver transplant team of Beijing Friendship Hospital affiliated with Capital Medical University. All three patients were positive for HBV surface antigen (HBsAg) and had a negative HBV DNA test result before transplantation. After auxiliary transplantations, HBsAg was found to be positive in two patients and negative in one patient. To avoid graft infection of HBV, entecavir-based therapy was employed and the remnant native livers of the recipients were removed 51-878 days after liver transplantation. Then, serum conversions of HBsAg were found in all three cases. For the first time, this case series shows the possibility of blocking the transmission of HBV from a native liver to a graft in auxiliary transplantation by entecavir-based therapy. Among the cases, a left lobe graft was successfully implanted as a replacement of the right lobe of the recipient, which is also discussed.

The frequency of rare and monogenic diseases in pediatric organ transplant recipients in Italy

Background

Rare diseases are chronic and life-threatening disorders affecting < 1 person every 2,000. For most of them, clinical symptoms and signs can be observed at birth or childhood. Approximately 80% of all rare diseases have a genetic background and most of them are monogenic conditions. In addition, while the majority of these diseases is still incurable, early diagnosis and specific treatment can improve patients’ quality of life. Transplantation is among the therapeutic options and represents the definitive treatment for end-stage organ failure, both in children and adults. The aim of this paper was to analyze, in a large cohort of Italian patients, the main rare genetic diseases that led to organ transplantation, specifically pointing the attention on the pediatric cohort.

Results

To the purpose of our analysis, we considered heart, lung, liver and kidney transplants included in the Transplant Registry (TR) of the Italian National Transplantation Center in the 2002–2019 timeframe. Overall, 49,404 recipients were enrolled in the cohort, 5.1% of whom in the pediatric age. For 40,909 (82.8%) transplant recipients, a disease diagnosis was available, of which 38,615 in the adult cohort, while 8,495 patients (17.2%) were undiagnosed. There were 128 disease categories, and of these, 117 were listed in the main rare disease databases. In the pediatric cohort, 2,294 (5.6%) patients had a disease diagnosis: of the 2,126 (92.7%) patients affected by a rare disease, 1,402 (61.1%) presented with a monogenic condition. As expected, the frequencies of pathologies leading to organ failure were different between the pediatric and the adult cohort. Moreover, the pediatric group was characterized, compared to the adult one, by an overall better survival of the graft at ten years after transplant, with the only exception of lung transplants. When comparing survival considering rare vs non-rare diseases or rare and monogenic vs rare non-monogenic conditions, no differences were highlighted for kidney and lung transplants, while rare diseases had a better survival in liver as opposed to heart transplants.

Conclusions

This work represents the first national survey analyzing the main genetic causes and frequencies of rare and/or monogenic diseases leading to organ failure and requiring transplantation both in adults and children.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02013-x.

Pediatric metabolic liver diseases: Evolving role of liver transplantation

Metabolic liver diseases (MLD) are the second most common indication for liver transplantation (LT) in children. This is based on the fact that the majority of enzymes involved in various metabolic pathways are present within the liver and LT can cure or at least control the disease manifestation. LT is also performed in metabolic disorders for end-stage liver disease, its sequelae including hepatocellular cancer. It is also performed for preventing metabolic crisis’, arresting progression of neurological dysfunction with a potential to reverse symptoms in some cases and for preventing damage to end organs like kidneys as in the case of primary hyperoxalosis and methyl malonic acidemia. Pathological findings in explant liver with patients with metabolic disease include unremarkable liver to steatosis, cholestasis, inflammation, variable amount of fibrosis, and cirrhosis. The outcome of LT in metabolic disorders is excellent except for patients with mitochondrial disorders where significant extrahepatic involvement leads to poor outcomes and hence considered a contraindication for LT. A major advantage of LT is that in the post-operative period most patients can discontinue the special formula which they were having prior to the transplant and this increases their well-being and improves growth parameters. Auxiliary partial orthotopic LT has been described for patients with noncirrhotic MLD where a segmental graft is implanted in an orthotopic position after partial resection of the native liver. The retained native liver can be the potential target for future gene therapy when it becomes a clinical reality.

Liver Organoids: Formation Strategies and Biomedical Applications

The liver is the most important digestive organ in the body. Several studies have explored liver biology and diseases related to the liver. However, most of these studies have only explored liver development, mechanism of liver regeneration and pathophysiology of liver diseases mainly based on two-dimensional (2D) cell lines and animal models. Traditional 2D cell lines do not represent the complex three-dimensional tissue architecture whereas animal models are limited by inter-species differences. These shortcomings limit understanding of liver biology and diseases. Liver organoid technology is effective in elucidating structural and physiological characteristics and basic tissue-level functions of liver tissue. In this review, formation strategies and a wide range of applications in biomedicine of liver organoid are summarized. Liver organoids are derived from single type cell culture, such as induced pluripotent stem cells (iPSCs), adult stem cells, primary hepatocytes, and primary cholangiocytes and multi-type cells co-culture, such as iPSC-derived hepatic endoderm cells co-cultured with mesenchymal stem cells and umbilical cord-derived endothelial cells. In vitro studies report that liver organoids are a promising model for regenerative medicine, organogenesis, liver regeneration, disease modelling, drug screening and personalized treatment. Liver organoids are a promising in vitro model for basic research and for development of clinical therapeutic interventions for hepatopathy.

UGT1A1-related Bilirubin Encephalopathy/Kernicterus in Adults

BACKGROUND AND AIMS

Bilirubin encephalopathy/kernicterus is very rare in adults. This study is aimed to investigate the clinical manifestations and genetic features of two patients with UGT1A1-related kernicterus.

METHODS

Sanger sequencing analysis was performed to identify UGT1A1 gene mutations in the patients and their families. Bioinformatics analysis was used to predict the potential functional effects of novel missense mutations. Clinical manifestations and biochemical parameters were collected and analyzed.

RESULTS

Two patients with Crigler-Najjar syndrome type II (CNS2) developed kernicterus in adulthood. Sanger sequencing identified a compound heterozygous mutation in the UGT1A1 gene in patient 1, which was inherited from his mother (G71R) and his father (c.-3279T>G; S191F). Patient 2 carried three heterozygous mutations, namely G71R, R209W and M391K; among which, the M391K mutation has not been reported before. Multiple prediction software showed that the M391K mutation was pathogenic. Symptoms were relieved in the two patients after phenobarbital and artificial liver support treatment. Patient 1 also underwent liver transplantation.

CONCLUSIONS

Adults with CNS2 are at risk for kernicterus. Phenobarbital treatment is beneficial for maintaining bilirubin levels and preventing kernicterus.

Genetically blocking HPD via CRISPR-Cas9 protects against lethal liver injury in a pig model of tyrosinemia type I

Hereditary tyrosinemia type I (HT1) results from the loss of fumarylacetoacetate hydrolase (FAH) activity and can lead to lethal liver injury (LLI). Therapeutic options for HT1 remain limited. The FAH^−/− pig, a well-characterized animal model of HT1, represents a promising candidate for testing novel therapeutic approaches to treat this condition. Here, we report an improved single-step method to establish a biallelic (FAH^−/−) mutant porcine model using CRISPR-Cas9 and cytoplasmic microinjection. We also tested the feasibility of rescuing HT1 pigs through inactivating the 4-hydroxyphenylpyruvic acid dioxygenase (HPD) gene, which functions upstream of the pathogenic pathway, rather than by directly correcting the disease-causing gene as occurs with traditional gene therapy. Direct intracytoplasmic delivery of CRISPR-Cas9 targeting HPD before intrauterine death reprogrammed the tyrosine metabolism pathway and protected pigs against FAH deficiency-induced LLI. Characterization of the F1 generation revealed consistent liver-protective features that were germline transmissible. Furthermore, HPD ablation ameliorated oxidative stress and inflammatory responses and restored the gene profile relating to liver metabolism homeostasis. Collectively, this study not only provided a novel large animal model for exploring the pathogenesis of HT1, but also demonstrated that CRISPR-Cas9-mediated HPD ablation alleviated LLI in HT1 pigs and represents a potential therapeutic option for the treatment of HT1.

Human biomimetic liver microphysiology systems in drug development and precision medicine

Microphysiology systems (MPS), also called organs-on-chips and tissue chips, are miniaturized functional units of organs constructed with multiple cell types under a variety of physical and biochemical environmental cues that complement animal models as part of a new paradigm of drug discovery and development. Biomimetic human liver MPS have evolved from simpler 2D cell models, spheroids and organoids to address the increasing need to understand patient-specific mechanisms of complex and rare diseases, the response to therapeutic treatments, and the absorption, distribution, metabolism, excretion and toxicity of potential therapeutics. The parallel development and application of transdisciplinary technologies, including microfluidic devices, bioprinting, engineered matrix materials, defined physiological and pathophysiological media, patient-derived primary cells, and pluripotent stem cells as well as synthetic biology to engineer cell genes and functions, have created the potential to produce patient-specific, biomimetic MPS for detailed mechanistic studies. It is projected that success in the development and maturation of patient-derived MPS with known genotypes and fully matured adult phenotypes will lead to advanced applications in precision medicine. In this Review, we examine human biomimetic liver MPS that are designed to recapitulate the liver acinus structure and functions to enhance our knowledge of the mechanisms of disease progression and of the absorption, distribution, metabolism, excretion and toxicity of therapeutic candidates and drugs as well as to evaluate their mechanisms of action and their application in precision medicine and preclinical trials.

Cholestatic liver disease: Practice guidelines from the Saudi Association for the Study of Liver diseases and Transplantation

Cholestatic liver diseases (CLDs) are a group of diseases characterized by jaundice and cholestasis as the main presentation with different complications, which have considerable impact on the liver and can lead to end-stage liver disease, cirrhosis, and liver-related complications. In the last few years, tremendous progress has been made in understanding the pathophysiology, diagnosis, and treatment of patients with these conditions. However, several aspects related to the management of CLDs remain deficient and unclear. Due to the lack of recommendations that can help in the management, treatment of those conditions, the Saudi Association for the Study of Liver diseases and Transplantation (SASLT) has created a task force group to develop guidelines related to CLDs management in order to provide a standard of care for patients in need. These guidelines provide general guidance for health care professionals to optimize medical care for patients with CLDs for both adult and pediatric populations, in association with clinical judgments to be considered on a case-by-case basis. These guidelines describe common CLDs in Saudi Arabia, with recommendations on the best approach for diagnosis and management of different diseases based on the Grading of Recommendation Assessment (GRADE), combined with a level of evidence available in the literature.

Successful living donor liver transplantation plus domino-auxiliary partial orthotopic liver transplantation for pediatric patients with metabolic disorders

PURPOSE

To investigate the efficacy of living donor liver transplantation (LDLT) plus domino-auxiliary partial orthotopic liver transplantation (D-APOLT) in pediatric patients with metabolic disorders.

METHODS

From May 2017 to October 2018, two patients with ornithine aminotransferase deficiency (OTCD) and one patient with type I Crigler-Najjar syndrome (CNS1) received LDLT, their livers were prepared as donors for D-APOLT. Two patients with CNS1 received domino liver grafts from OTCD patients; one OTCD patient received a domino liver graft from a CNS1 patient.

RESULTS

The mean follow-up was 26.6 months. The liver function and ammonia remained in the normal range at the end of the follow-up in all recipients. One D-APOLT patient experienced portal vein thrombosis 2 days after transplantation and required reoperation, this patient presented an imbalance of portal blood perfusion between the native and the domino liver at 8 months after liver transplant. The imbalance was improved by interventional radiology treatment. Two LDLT patients experienced early mild acute rejection.

CONCLUSIONS

The non-cirrhotic livers from pediatric patients with metabolic liver disease can be used as domino donor grafts for selected pediatric patients with different metabolic liver disease. D-APOLT achieves ideal recipient outcomes and provides a strategy to expand donor source for children.

Combined liver-kidney transplantation for rare diseases

Combined liver and kidney transplantation (CLKT) is indicated in patients with failure of both organs, or for the treatment of end-stage chronic kidney disease (ESKD) caused by a genetic defect in the liver. The aim of the present review is to provide the most up-to-date overview of the rare conditions as indications for CLKT. They are major indications for CLKT in children. However, in some of them (e.g., atypical hemolytic uremic syndrome or primary hyperoxaluria), CLKT may be required in adults as well. Primary hyperoxaluria is divided into three types, of which type 1 and 2 lead to ESKD. CLKT has been proven effective in renal function replacement, at the same time preventing recurrence of the disease. Nephronophthisis is associated with liver fibrosis in 5% of cases and these patients are candidates for CLKT. In alpha 1-antitrypsin deficiency, hereditary C3 deficiency, lecithin cholesterol acyltransferase deficiency and glycogen storage diseases, glomerular or tubulointerstitial disease can lead to chronic kidney disease. Liver transplantation as a part of CLKT corrects underlying genetic and consequent metabolic abnormality. In atypical hemolytic uremic syndrome caused by mutations in the genes for factor H, successful CLKT has been reported in a small number of patients. However, for this indication, CLKT has been largely replaced by eculizumab, an anti-C5 antibody. CLKT has been well established to provide immune protection of the transplanted kidney against donor-specific antibodies against class I HLA, facilitating transplantation in a highly sensitized recipient.

Organoids to model liver disease

The organoid model represents a major breakthrough in cell biology that has revolutionised biomedical research. Organoids are 3D physiological in vitro structures that recapitulate morphological and functional features of in vivo tissues and offer significant advantages over traditional cell culture methods. Liver organoids are of particular interest because of the pleiotropy of functions exerted by the human liver, their utility to model different liver diseases, and their potential application as cell-based therapies in regenerative medicine. Moreover, because they can be derived from patient tissues, organoid models offer new perspectives in personalised medicine and drug discovery. In this review, we discuss the current liver organoid models for the study of liver disease.

Gene therapy for alpha 1-antitrypsin deficiency with an oxidant-resistant human alpha 1-antitrypsin

Alpha 1-antitrypsin (AAT) deficiency, a hereditary disorder characterized by low serum levels of functional AAT, is associated with early development of panacinar emphysema. AAT inhibits serine proteases, including neutrophil elastase, protecting the lung from proteolytic destruction. Cigarette smoke, pollution, and inflammatory cell–mediated oxidation of methionine (M) 351 and 358 inactivates AAT, limiting lung protection. In vitro studies using amino acid substitutions demonstrated that replacing M351 with valine (V) and M358 with leucine (L) on a normal M1 alanine (A) 213 background provided maximum antiprotease protection despite oxidant stress. We hypothesized that a onetime administration of a serotype 8 adeno-associated virus (AAV8) gene transfer vector coding for the oxidation-resistant variant AAT (A213/V351/L358; 8/AVL) would maintain antiprotease activity under oxidant stress compared with normal AAT (A213/M351/M358; 8/AMM). 8/AVL was administered via intravenous (IV) and intrapleural (IPL) routes to C57BL/6 mice. High, dose-dependent AAT levels were found in the serum and lung epithelial lining fluid (ELF) of mice administered 8/AVL or 8/AMM by IV or IPL. 8/AVL serum and ELF retained serine protease–inhibitory activity despite oxidant stress while 8/AMM function was abolished. 8/AVL represents a second-generation gene therapy for AAT deficiency providing effective antiprotease protection even with oxidant stress.

A gene transfer-based therapeutic to deliver oxidant-resistant alpha 1-antitrypsin (AAT) protects mice with AAT deficiency from lung destruction.

Long-Term Follow-Up of the First in Human Intravascular Delivery of AAV for Gene Transfer: AAV2-hFIX16 for Severe Hemophilia B

Adeno-associated virus (AAV) vectors are a leading platform for gene-based therapies for both monogenic and complex acquired disorders. The success of AAV gene transfer highlights the need to answer outstanding clinical questions of safety, durability, and the nature of the human immune response to AAV vectors. Here, we present longitudinal follow-up data of subjects who participated in the first trial of a systemically delivered AAV vector. Adult males (n = 7) with severe hemophilia B received an AAV2 vector at doses ranging from 8 × 10¹⁰ to 2 × 10¹² vg/kg to target hepatocyte-specific expression of coagulation factor IX; a subset (n = 4) was followed for 12-15 years post-vector administration. No major safety concerns were observed. There was no evidence of sustained hepatic toxicity or development of hepatocellular carcinoma as assessed by liver transaminase values, serum α-fetoprotein, and liver ultrasound. Subjects demonstrated persistent, increased AAV neutralizing antibodies (NAbs) to the infused AAV serotype 2 (AAV2) as well as all other AAV serotypes tested (AAV5 and AAV8) for the duration of follow-up. These data represent the longest available longitudinal follow-up data of subjects who received intravascular AAV and support the preliminary safety of intravascular AAV administration at the doses tested in adults. Data demonstrate, for the first time, the persistence of high-titer, multi-serotype cross-reactive AAV NAbs for up to 15 years post- AAV vector administration. Our observations are broadly applicable to the development of AAV-mediated gene therapy.

Post-transplantation Outcomes in Patients with PA or MMA: A Review of the Literature

Introduction

Liver transplantation is recognised as a treatment option for patients with propionic acidemia (PA) and those with methylmalonic acidemia (MMA) without renal impairment. In patients with MMA and moderate-to-severe renal impairment, combined liver–kidney transplantation is indicated. However, clinical experience of these transplantation options in patients with PA and MMA remains limited and fragmented. We undertook an overview of post-transplantation outcomes in patients with PA and MMA using the current available evidence.

Methods

A literature search identified publications on the use of transplantation in patients with PA and MMA. Publications were considered if they presented adequate demographic and outcome data from patients with PA or MMA. Publications that did not report any specific outcomes for patients or provided insufficient data were excluded.

Results

Seventy publications were identified of which 38 were full papers. A total of 373 patients underwent liver/kidney/combined liver–kidney transplantation for PA or MMA. The most typical reason for transplantation was recurrent metabolic decompensation. A total of 27 post-transplant deaths were reported in patients with PA [14.0% (27/194)]. For patients with MMA, 18 post-transplant deaths were reported [11% (18/167)]. A total of 62 complications were reported in 115 patients with PA (54%) with cardiomyopathy (n = 12), hepatic arterial thrombosis (HAT; n = 14) and viral infections (n = 12) being the most commonly reported. A total of 52 complications were reported in 106 patients with MMA (49%) with viral infections (n = 14) and renal failure/impairment (n = 10) being the most commonly reported.

Conclusions

Liver transplantation and combined liver–kidney transplantation appears to benefit some patients with PA or MMA, respectively, but this approach does not provide complete correction of the metabolic defect and some patients remain at risk from disease-related and transplantation-related complications, including death. Thus, all treatment avenues should be exhausted before consideration of organ transplantation and the benefits of this approach must be weighed against the risk of perioperative complications on an individual basis.

Human liver stem cells express UGT1A1 and improve phenotype of immunocompromised Crigler Najjar syndrome type I mice

Crigler Najjar Syndrome type I (CNSI) is a rare recessive disorder caused by mutations in the Ugt1a1 gene. There is no permanent cure except for liver transplantation, and current therapies present several shortcomings. Since stem cell-based therapy offers a promising alternative for the treatment of this disorder, we evaluated the therapeutic potential of human liver stem cells (HLSC) in immune-compromised NOD SCID Gamma (NSG)/Ugt1^−/− mice, which closely mimic the pathological manifestations in CNSI patients. To assess whether HLSC expressed UGT1A1, decellularised mouse liver scaffolds were repopulated with these cells. After 15 days’ culture ex vivo, HLSC differentiated into hepatocyte-like cells showing UGT1A1 expression and activity. For the in vivo human cell engraftment and recovery experiments, DiI-labelled HLSC were injected into the liver of 5 days old NSG/Ugt1^−/− pups which were analysed at postnatal Day 21. HLSC expressed UGT1A1 in vivo, induced a strong decrease in serum unconjugated bilirubin, thus significantly improving phenotype and survival compared to untreated controls. A striking recovery from brain damage was also observed in HLSC-injected mutant mice versus controls. Our proof-of-concept study shows that HLSC express UGT1A1 in vivo and improve the phenotype and survival of NSG/Ugt1^−/− mice, and show promises for the treatment of CNSI.

Targeted Next-Generation Sequencing in Diagnostic Approach to Monogenic Cholestatic Liver Disorders-Single-Center Experience

Objective: To evaluate the clinical utility of panel-based NGS in the diagnostic approach of monogenic cholestatic liver diseases. Study design: Patients with diagnosis of chronic cholestatic liver disease of an unknown etiology underwent NGS of targeted genes panel. Group 1 included five patients (prospectively recruited) hospitalized from January to December 2017 while group 2 included seventeen patients (retrospectively recruited) hospitalized from 2010 to 2017 presenting with low-GGT PFIC phenotype (group 2a, 11 patients) or indeterminant cholestatic liver cirrhosis (group 2b, 6 patients). Results: Among 22 patients enrolled into the study, 21 various pathogenic variants (including 11 novel) in 5 different genes (including ABCB11, ABCB4, TJP2, DGUOK, CYP27A1) were identified. The molecular confirmation was obtained in 15 out of 22 patients (68%). In group 1, two out of five patients presented with low-GGT cholestasis, and were diagnosed with BSEP deficiency. Out of three patients presenting with high-GGT cholestasis, one patient was diagnosed with PFIC-3, and the remaining two were not molecularly diagnosed. In group 2a, seven out of eleven patients, were diagnosed with BSEP deficiency and two with TJP-2 deficiency. In group 2b, three out of six patients were molecularly diagnosed; one with PFIC-3, one with CYP27A1 deficiency, and one with DGUOK deficiency. Conclusions: Panel-based NGS appears to be a very useful tool in diagnosis of monogenic cholestatic liver disorders in cases when extrahepatic causes have been primarily excluded. NGS presented the highest diagnosis rate to identify the molecular background of cholestatic liver diseases presenting with a low-GGT PFIC phenotype.

Lipid nanoparticle technology for therapeutic gene regulation in the liver

Hereditary genetic disorders, cancer, and infectious diseases of the liver affect millions of people around the globe and are a major public health burden. Most contemporary treatments offer limited relief as they generally aim to alleviate disease symptoms. Targeting the root cause of diseases originating in the liver by regulating malfunctioning genes with nucleic acid-based drugs holds great promise as a therapeutic approach. However, employing nucleic acid therapeutics in vivo is challenging due to their unfavorable characteristics. Lipid nanoparticle (LNP) delivery technology is a revolutionary development that has enabled clinical translation of gene therapies. LNPs can deliver siRNA, mRNA, DNA, or gene-editing complexes, providing opportunities to treat hepatic diseases by silencing pathogenic genes, expressing therapeutic proteins, or correcting genetic defects. Here we discuss the state-of-the-art LNP technology for hepatic gene therapy including formulation design parameters, production methods, preclinical development and clinical translation.

Liver organoids: from basic research to therapeutic applications

Organoid cultures have emerged as an alternative in vitro system to recapitulate tissues in a dish. While mouse models and cell lines have furthered our understanding of liver biology and associated diseases, they suffer in replicating key aspects of human liver tissue, in particular its complex architecture and metabolic functions. Liver organoids have now been established for multiple species from induced pluripotent stem cells, embryonic stem cells, hepatoblasts and adult tissue-derived cells. These represent a promising addition to our toolbox to gain a deeper understanding of this complex organ. In this perspective we will review the advances in the liver organoid field, its limitations and potential for biomedical applications.

Perioperative characteristics and management of liver transplantation for isolated methylmalonic acidemia-the largest experience in China

Background

There are few detailed consensus and guidelines on perioperative clinical characteristics of liver transplantation (LT) in patients with methylmalonic acidemia (MMA). This retrospective study investigated details of the clinical course and individualized treatment plan of the center with largest experience in China.

Methods

A total of 7 MMA patients undergoing LT in Beijing Friendship Hospital from June 2013 to December 2017 were enrolled in the study, whose clinical data (clinical characteristics, laboratory findings, chronological changes in urine MMA levels, treatment, etc.) during perioperative period were analyzed retrospectively. All the patients received strict postoperative management.

Results

All the 7 cases were confirmed to have isolated MMA, among which, 3 cases received living donor liver transplantation (LDLT), 4 cases received deceased donor liver transplantation (DDLT). A wild fluctuate of metabolic condition was observed within the first few days after surgery and two weeks after LT, the mean base excess of blood value (BE-B) restored to normal whereas plasma bicarbonate (HCO₃ ^-) was still below normal value even with intermittent sodium bicarbonate correction. It also showed marked reduction in propionylcarnitine (C3) and C3/C2 level and the mean urine MMA by gas chromatography-mass spectrometry (GC-MS) was reduced by 81.7% (P<0.01) but remained >72× higher than upper limit of normal. The metabolism-correcting medications were administered as before. The renal function of one case with renal insufficiency before LT (serum creatinine rising) maintained stable by adjusting the immunosuppressive regimen during the observation period. All patients survive to date.

Conclusions

LT is an effective treatment to prevent metabolic crisis, but patients with MMA tend to be metabolically fragile even after surgery. During perioperative period, close monitoring should be given for acidosis episodes so as to implement sodium bicarbonate correction. Metabolism-correcting medications are still needed. Special immunosuppressive regimen is an effective way of maintaining renal function for those with kidney dysfunction.

Technique and outcome of domino liver transplantation from patients with maple syrup urine disease: Expanding the donor pool for live donor liver transplantation

AIM/BACKGROUND

Domino liver transplantation (DLT) using liver allografts from patients with metabolic disorders enhances organ utilization. Short- and long-term course and outcome of these patients can impact the decision to offer this procedure to patients, especially those with diseases that can potentially be cured with liver transplant. We reviewed the outcomes of DLT from maple syrup urine disease (MSUD) patients in our large academic pediatric and adult transplant program.

METHODS

All patients receiving DLT were analyzed retrospectively with a minimum of one-year follow-up period for patient and donor characteristics, early and late postoperative complications and patient and graft survival with their MSUD donors in terms of age, weight, MELD/PELD scores, cold ischemia time, postoperative leucine levels, and peak ALT (alanine aminotransferase) levels during the first 48 postoperative hours.

RESULTS

Between 2006 and May 2019, 21 patients underwent domino liver transplantation with live donor allografts from MSUD patients. Four patients transplanted for different metabolic diseases are focus of a separate report. Seventeen patients with minimum one-year follow-up period are reported herein. The indications were primary sclerosing cholangitis (PSC, n = 4), congenital hepatic fibrosis (CHF, n = 2), alpha-1 antitrypsin deficiency (A-1 ATD, n = 2), progressive familial intrahepatic cholestasis (PFIC, n = 2), cystic fibrosis (n = 1), primary biliary cirrhosis (PBC, n = 1), neonatal hepatitis (n = 1), embryonal sarcoma (n = 1), Caroli disease (n = 1), hepatocellular carcinoma (HCC, n = 1), and chronic rejection after liver transplantations for PSC (n = 1). All patients and grafts survived at median follow-up of 6.4 years (range 1.2-12.9 years). Median domino recipient age was 16.2 years (range 0.6-64.6 years) and median MSUD recipient age was 17.6 years (range 4.8-32.1 years). There were no vascular complications during the early postoperative period, one patient had portal vein thrombosis 3 years after DLT and a meso-Rex bypass was successfully performed. Small for size syndrome (SFSS) occurred in reduced left lobe DLT recipient and was managed successfully with conservative management. Biliary stricture developed in 2 patients and was resolved by stenting. Comparison between DLT and MSUD recipients' peak postoperative ALT results and PELD/MELD scores showed lower levels in DLT group (P-value <.05).

CONCLUSIONS

Patient and graft survival in DLT from MSUD donors was excellent at short- and long-term follow-up. Metabolic functions have been normal in all recipients on a normal unrestricted protein diet. Ischemia preservation injury based on peak ALT was significantly decreased in DLT recipients. Domino transplantation from pediatric and adult recipients with selected metabolic diseases should be increasingly considered as an excellent option and alternative to deceased donor transplantation, thereby expanding the living donor pool. This, to date, is the largest world experience in DLT utilizing livers from patients with MSUD.

Domino liver transplantation for select metabolic disorders: Expanding the living donor pool

Domino liver transplantation (DLT) involves transplanting liver from a patient with metabolic disease into a patient with end-stage liver disease with the expectation that the recipient will not develop the metabolic syndrome or the recurrent syndrome will have minimal affect. The domino donor gets a deceased donor or a segment of live-donor liver through the deceased donor organ allocation system. Waitlist mortality for the domino recipient exceeds morbidity associated with getting the donor disease. Between 2015 and 2017, four patients with three metabolic disorders at UPMC Children's Hospital of Pittsburgh underwent DLT with domino allografts from maple syrup urine disease (MSUD) patients. These included patients with propionic acidemia (PA) (n = 1), Crigler-Najjar (CN) syndrome type-1 (n = 2), and carbamoyl phosphate synthetase deficiency (CPSD) (n = 1). Mean follow-up was 1.6 years (range 1.1-2.1 years). Total bilirubin levels normalized postoperatively in both CN patients and they maintain normal allograft function. The PA patient had normal to minimal elevations of isoleucine and leucine, and no other abnormalities on low protein diet supplemented with a low methionine and valine free formula. No metabolic crises have occurred. The patient with CPSD takes normal baby food. No elevation in ammonia levels have been observed in any of the patients. DLT for a select group of metabolic diseases alleviated the recipients of their metabolic defect with minimal evidence of transferrable-branched chain amino acid elevations or clinical MSUD despite increased protein intake. DLT using allografts with MSUD expands the live donor liver pool and should be considered for select metabolic diseases that may have a different enzymatic deficiency.

Messenger RNA therapy for rare genetic metabolic diseases

Decades of intense research in molecular biology and biochemistry are fructifying in the emergence of therapeutic messenger RNAs (mRNA) as a new class of drugs. Synthetic mRNAs can be sequence optimised to improve translatability into proteins, as well as chemically modified to reduce immunogenicity and increase chemical stability using naturally occurring uridine modifications. These structural improvements, together with the development of safe and efficient vehicles that preserve mRNA integrity in circulation and allow targeted intracellular delivery, have paved the way for mRNA-based therapeutics. Indeed, mRNAs formulated into biodegradable lipid nanoparticles are currently being tested in preclinical and clinical studies for multiple diseases including cancer immunotherapy and vaccination for infectious diseases. An emerging application of mRNAs is the supplementation of proteins that are not expressed or are not functional in a regulated and tissue-specific manner. This so-called 'protein replacement therapy' could represent a solution for genetic metabolic diseases currently lacking effective treatments. Here we summarise this new class of drugs and discuss the preclinical evidence supporting the potential of liver-mediated mRNA therapy for three rare genetic conditions: methylmalonic acidaemia, acute intermittent porphyria and ornithine transcarbamylase deficiency.

Coupling AAV-mediated promoterless gene targeting to SaCas9 nuclease to efficiently correct liver metabolic diseases

Non-integrative AAV-mediated gene therapy in the liver is effective in adult patients, but faces limitations in pediatric settings due to episomal DNA loss during hepatocyte proliferation. Gene targeting is a promising approach by permanently modifying the genome. We previously rescued neonatal lethality in Crigler-Najjar mice by inserting a promoterless human uridine glucuronosyl transferase A1 (UGT1A1) cDNA in exon 14 of the albumin gene, without the use of nucleases. To increase recombination rate and therapeutic efficacy, here we used CRISPR/SaCas9. Neonatal mice were transduced with two AAVs: one expressing the SaCas9 and sgRNA, and one containing a promoterless cDNA flanked by albumin homology regions. Targeting efficiency increased ~26-fold with an eGFP reporter cDNA, reaching up to 24% of eGFP-positive hepatocytes. Next, we fully corrected the diseased phenotype of Crigler-Najjar mice by targeting the hUGT1A1 cDNA. Treated mice had normal plasma bilirubin up to 10 months after administration, hUGT1A1 protein levels were ~6-fold higher than in WT liver, with a 90-fold increase in recombination rate. Liver histology, inflammatory markers, and plasma albumin were normal in treated mice, with no off-targets in predicted sites. Thus, the improved efficacy and reassuring safety profile support the potential application of the proposed approach to other liver diseases.

The complexity of a monogenic neurodegenerative disease: More than two decades of therapeutic driven research into Niemann-Pick type C disease

Niemann-Pick type C (NP-C) disease is a rare and fatal neurodegenerative disease typified by aberrations in intracellular lipid transport. Cholesterol and other lipids accumulate in the late endosome/lysosome of all diseased cells thereby causing neuronal and visceral atrophy. A cure for NP-C remains elusive despite the extensive molecular advances emanating from the identification of the primary genetic defect in 1997. Penetration of the blood-brain barrier and efficacy in the viscera are prerequisites for effective therapy, however the rarity of NP-C disease is the major impediment to progress. Disease diagnosis is challenging and establishment of appropriate test populations for clinical trials difficult. Fortunately, disease models that span the diversity of microbial and metazoan life have been utilized to advance the quest for a therapy. The complexity of lipid storage in this disorder and in the model systems, has led to multiple theories on the primary disease mechanism and consequently numerous and varied proposed interventions. Here, we conduct an evaluation of these studies.

Methylmalonic acidemia/propionic acidemia - the biochemical presentation and comparing the outcome between liver transplantation versus non-liver transplantation groups

Background

Most patients with isolated methylmalonic acidemia (MMA) /propionic acidemia (PA) presenting during the neonatal period with acute metabolic distress are at risk for death and significant neurodevelopmental disability. The nationwide newborn screening for MMA/PA has been in place in Taiwan from January, 2000 and data was collected until December, 2016.

Results

During the study period, 3,155,263 newborns were screened. The overall incidence of MMA mutase type cases was 1/121,356 (n = 26), 1 cobalamin B was detected and that for PA cases (n = 4) was 1/788,816. The time of referral is 8.8 days for MMA patients, and 7.5 days for PA patients. The MMA mutase type patients have higher AST, ALT, and NH₃ values as well as a lower pH value (p < 0.05). The mean age for liver transplantation (LT) is 402 days (range from 0.6–6.7 yr) with 16 out of 20 cases (80.0%) using living donors. The mean admission length shortened from 90.6 days/year (pre-LT) to 5.3 days/year (at 3rd year post-LT) (p < 0.0005). Similarly, the tube feeding ratio decreased from 67.8 to 0.50% (p < 0.00005). The anxiety level of the caregiver was reduced from 33.4 to 27.2 after LT (p = 0.001) and the DQ/IQ performance of the patients was improved after LT from 50 to 60.1 (p = 0.07).

Conclusion

MMA/PA patients with LT do survive and have reduced admission time, reduced tube feeding and the caregiver is less anxious.

Preclinical Development of an AAV8-hUGT1A1 Vector for the Treatment of Crigler-Najjar Syndrome

Adeno-associated viruses (AAVs) are among the most efficient vectors for liver gene therapy. Results obtained in the first hemophilia clinical trials demonstrated the long-term efficacy of this approach in humans, showing efficient targeting of hepatocytes with both self-complementary (sc) and single-stranded (ss) AAV vectors. However, to support clinical development of AAV-based gene therapies, efficient and scalable production processes are needed. In an effort to translate to the clinic an approach of AAV-mediated liver gene transfer to treat Crigler-Najjar (CN) syndrome, we developed an (ss)AAV8 vector carrying the human UDP-glucuronosyltransferase family 1-member A1 (hUGT1A1) transgene under the control of a liver-specific promoter. We compared our construct with similar (sc)AAV8 vectors expressing hUGT1A1, showing comparable potency in vitro and in vivo. Conversely, (ss)AAV8-hUGT1A1 vectors showed superior yields and product homogeneity compared with their (sc) counterpart. We then focused our efforts in the scale-up of a manufacturing process of the clinical product (ss)AAV8-hUGT1A1 based on the triple transfection of HEK293 cells grown in suspension. Large-scale production of this vector had characteristics identical to those of small-scale vectors produced in adherent cells. Preclinical studies in animal models of the disease and a good laboratory practice (GLP) toxicology-biodistribution study were also conducted using large-scale preparations of vectors. These studies demonstrated long-term safety and efficacy of gene transfer with (ss)AAV8-hUGT1A1 in relevant animal models of the disease, thus supporting the clinical translation of this gene therapy approach for the treatment of CN syndrome.

A Novel Pathogenic UGT1A1 Variant in a Sudanese Child with Type 1 Crigler-Najjar Syndrome

Uridine diphosphate glucuronosyltransferases (UGTs) are key enzymes responsible for the body's ability to process a variety of endogenous and exogenous compounds. Significant gains in understanding UGT function have come from the analysis of variants seen in patients. We cared for a Sudanese child who showed clinical features of type 1 Crigler-Najjar syndrome (CN-1), namely severe unconjugated hyperbilirubinemia leading to liver transplantation. CN-1 is an autosomal recessive disorder caused by damaging mutations in the gene for UGT1A1, the hepatic enzyme responsible for bilirubin conjugation in humans. Clinical genetic testing was unable to identify a known pathogenic UGT1A1 mutation in this child. Instead, a novel homozygous variant resulting in an in-frame deletion, p.Val275del, was noted. Sanger sequencing demonstrated that this variant segregated with the disease phenotype in this family. We further performed functional testing using recombinantly expressed UGT1A1 with and without the patient variant, demonstrating that p.Val275del results in a complete lack of glucuronidation activity, a hallmark of CN-1. Sequence analysis of this region shows a high degree of conservation across all known catalytically active human UGTs, further suggesting that it plays a key role in the enzymatic function of UGTs. Finally, we note that the patient's ethnicity likely played a role in his variant being previously undescribed and advocate for greater diversity and inclusion in genomic medicine.

Auxiliary Partial Orthotopic Liver Transplantation for Monogenic Metabolic Liver Diseases: Single-Centre Experience

PURPOSE

Auxiliary partial orthotopic liver transplantation (APOLT) in metabolic liver disease (MLD) has the advantage of correcting the metabolic defect, preserving the native liver for gene therapy in the future with the possibility of withdrawal of immunosuppression.

METHODS

Retrospective analysis of safety and efficacy of APOLT in correcting the underlying defect and its impact on neurological status of children with MLD.

RESULTS

A total of 13 APOLT procedures were performed for MLD during the study period. The underlying aetiologies being propionic acidemia (PA)-5, citrullinemia type 1 (CIT1)-3 and Crigler-Najjar syndrome type 1 (CN1)-5 cases respectively. Children with PA and CIT1 had a median of 8 and 4 episodes of decompensation per year, respectively, before APOLT and had a mean social developmental quotient (DQ) of 49 (<3 standard deviations) as assessed by Vineland Social Maturity Scale prior to liver transplantation. No metabolic decompensation occurred in patients with PA and CIT1 intraoperatively or in the immediate post-transplant period on protein-unrestricted diet. Patients with CN1 were receiving an average 8-15 h of phototherapy per day before APOLT and had normal bilirubin levels without phototherapy on follow-up. We have 100% graft and patient survival at a median follow-up of 32 months. Progressive improvement in neurodevelopment was seen in children within 6 months of therapy with a median social DQ of 90.

CONCLUSIONS

APOLT is a safe procedure, which provides good metabolic control and improves the neurodevelopment in children with selected MLD.

Antigen-selective modulation of AAV immunogenicity with tolerogenic rapamycin nanoparticles enables successful vector re-administration

Gene therapy mediated by recombinant adeno-associated virus (AAV) vectors is a promising treatment for systemic monogenic diseases. However, vector immunogenicity represents a major limitation to gene transfer with AAV vectors, particularly for vector re-administration. Here, we demonstrate that synthetic vaccine particles encapsulating rapamycin (SVP[Rapa]), co-administered with AAV vectors, prevents the induction of anti-capsid humoral and cell-mediated responses. This allows successful vector re-administration in mice and nonhuman primates. SVP[Rapa] dosed with AAV vectors reduces B and T cell activation in an antigen-selective manner, inhibits CD8⁺ T cell infiltration in the liver, and efficiently blocks memory T cell responses. SVP[Rapa] immunomodulatory effects can be transferred from treated to naive mice by adoptive transfer of splenocytes, and is inhibited by depletion of CD25⁺ T cells, suggesting a role for regulatory T cells. Co-administration of SVP[Rapa] with AAV vector represents a powerful strategy to modulate vector immunogenicity and enable effective vector re-administration.