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

BACKGROUND & AIMS

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.

METHODS

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.

RESULTS

EcN-HT consumed tyrosine and produced L-DOPA (levodopa) in an in vitro 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.

CONCLUSIONS

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.

IMPACT AND IMPLICATIONS

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.

Engineering a transposon-associated TnpB-ωRNA system for efficient gene editing and phenotypic correction of a tyrosinaemia mouse model

Transposon-associated ribonucleoprotein TnpB is known to be the ancestry endonuclease of diverse Cas12 effector proteins from type-V CRISPR system. Given its small size (408 aa), it is of interest to examine whether engineered TnpB could be used for efficient mammalian genome editing. Here, we showed that the gene editing activity of native TnpB from Deinococcus radiodurans (ISDra2 TnpB) in mouse embryos was already higher than previously identified small-sized Cas12f1. Further stepwise engineering of noncoding RNA (ωRNA or reRNA) component of TnpB significantly elevated the nuclease activity of TnpB. Notably, an optimized TnpB-ωRNA system could be efficiently delivered in vivo with single adeno-associated virus (AAV) and corrected the disease phenotype in a tyrosinaemia mouse model. Thus, the engineered miniature TnpB system represents a new addition to the current genome editing toolbox, with the unique feature of the smallest effector size that facilitate efficient AAV delivery for editing of cells and tissues.

Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum

BACKGROUND

Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene. The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia. This study aimed to provide further insights into the clinical and genetic characteristics of HT III.

METHODS

A 3-year-old girl, identified through newborn screening, was diagnosed with HT III using targeted next-generation sequencing. A comprehensive literature review was conducted, and the clinical, biochemical, and genetic findings of previously reported HT III patients were summarized and analyzed.

RESULTS

The genetic analysis of the proband revealed compound heterozygous mutations in the HPD gene such as c.731C>T (p.A244V) and c.656C>T (p.T219M). Notably, the HPD p.A244V mutation had not been previously documented in public databases or the scientific literature. Bioinformatics analysis classified both variants as pathogenic variants. The patient exhibited persistent tyrosinemia, elevated levels of related metabolite derivatives, confirming the diagnosis of HT III. The review of previously published cases contributed to a better understanding of the clinical and genetic characteristics associated with HT III.

CONCLUSION

Early diagnosis and prompt treatment in infancy are crucial for managing HT III effectively. Dietary therapy, particularly during childhood, plays a significant role in disease management. The findings from this study enhance our understanding of the genotype-phenotype associations in HT III and emphasize the importance of early intervention for improved patient outcomes.

An Infant with Bilateral Keratitis: From Infectious to Genetic Diagnosis

BACKGROUND Tyrosinemia Type II (TYRII) is a rare autosomal recessive inborn error of metabolism caused by deficiency of tyrosine aminotransferase (TAT), leading to hypertyrosinemia. TYRII patients often present in the first year of life with ocular and cutaneous findings, including corneal ulcers, pseudodendritic keratitis, and palmoplantar hyperkeratosis. The corneal involvement is often mistaken for herpes simplex virus (HSV) keratitis, which is a much commoner condition. CASE REPORT A previously healthy 10-month-old male infant was referred to Ophthalmology for acute onset photophobia. Bilateral dendritiform corneal lesions raised the suspicion for herpetic keratitis. Additionally, a papular, crusted lesion was found on his thumb after a few days of hospitalization, also raising concerns about HSV. The patient's clinical condition seemed to improve under intravenous acyclovir and supportive treatment. A conjunctival swab and crusted lesion on the thumb were tested for HSV using a polymerase chain reaction (PCR) technique, and both were negative. Nevertheless, given the clinical presentation and the favorable course of signs and symptoms, hospital discharge was planned with oral acyclovir. It was halted by an alternative diagnosis of autosomal recessive inborn error of metabolism, tyrosinemia type II, confirmed by elevated plasma tyrosine level and later by molecular analysis requested as a confirmatory investigation by the genetics medical team. CONCLUSIONS The corneal involvement in TYRII is often mistaken for HSV keratitis, and clinical course alone should not halt further investigations to rule out TYRII. Clinicians should suspect TYRII clinically when its characteristic ocular dendritiform lesions are present, namely in infancy or early childhood, and even in the absence of its typical cutaneous palmoplantar hyperkeratosis plaques.

Neurocognitive outcome and mental health in children with tyrosinemia type 1 and phenylketonuria: A comparison between two genetic disorders affecting the same metabolic pathway

Tyrosinemia type 1 (TT1) and phenylketonuria (PKU) are both inborn errors of phenylalanine-tyrosine metabolism. Neurocognitive and behavioral outcomes have always featured in PKU research but received less attention in TT1 research. This study aimed to investigate and compare neurocognitive, behavioral, and social outcomes of treated TT1 and PKU patients. We included 33 TT1 patients (mean age 11.24 years; 16 male), 31 PKU patients (mean age 10.84; 14 male), and 58 age- and gender-matched healthy controls (mean age 10.82 years; 29 male). IQ (Wechsler-subtests), executive functioning (the Behavioral Rating Inventory of Executive Functioning), mental health (the Achenbach-scales), and social functioning (the Social Skills Rating System) were assessed. Results of TT1 patients, PKU patients, and healthy controls were compared using Kruskal-Wallis tests with post-hoc Mann-Whitney U tests. TT1 patients showed a lower IQ and poorer executive functioning, mental health, and social functioning compared to healthy controls and PKU patients. PKU patients did not differ from healthy controls regarding these outcome measures. Relatively poor outcomes for TT1 patients were particularly evident for verbal IQ, BRIEF dimensions "working memory", "plan and organize" and "monitor", ASEBA dimensions "social problems" and "attention problems", and for the SSRS "assertiveness" scale (all p values <0.001). To conclude, TT1 patients showed cognitive impairments on all domains studied, and appeared to be significantly more affected than PKU patients. More attention should be paid to investigating and monitoring neurocognitive outcome in TT1 and research should focus on explaining the underlying pathophysiological mechanism.

Biochemical and behavioural profile of NTBC treated Tyrosinemie type 1 mice

BACKGROUND

Tyrosinemia type 1 (HT1) is a rare metabolic disorder caused by a defect in the tyrosine catabolic pathway. Since HT1 patients are treated with NTBC, outcome improved and life expectancy greatly increased. However extensive neurocognitive and behavioural problems have been described, which might be related to treatment with NTBC, the biochemical changes induced by NTBC, or metabolites accumulating due to the enzymatic defect characterizing the disease.

OBJECTIVE

To study the possible pathophysiological mechanisms of brain dysfunction in HT1, we assessed blood and brain LNAA, and brain monoamine neurotransmitter metabolite levels in relation to behavioural and cognitive performance of HT1 mice.

DESIGN

C57BL/6 littermates were divided in three different experimental groups: HT1, heterozygous and wild-type mice (n = 10; 5 male). All groups were treated with NTBC and underwent cognitive and behavioural testing. One week after behavioural testing, blood and brain material were collected to measure amino acid profiles and brain monoaminergic neurotransmitter levels.

RESULTS

Irrespective of the genetic background, NTBC treatment resulted in a clear increase in brain tyrosine levels, whereas all other brain LNAA levels tended to be lower than their reference values. Despite these changes in blood and brain biochemistry, no significant differences in brain monoamine neurotransmitter (metabolites) were found and all mice showed normal behaviour and learning and memory.

CONCLUSION

Despite the biochemical changes, NTBC and genotype of the mice were not associated with poorer behavioural and cognitive function of the mice. Further research involving dietary treatment of FAH-/- are warranted to investigate whether this reveals the cognitive impairments that have been seen in treated HT1 patients.

A split prime editor with untethered reverse transcriptase and circular RNA template

Delivery and optimization of prime editors (PEs) have been hampered by their large size and complexity. Although split versions of genome-editing tools can reduce construct size, they require special engineering to tether the binding and catalytic domains. Here we report a split PE (sPE) in which the Cas9 nickase (nCas9) remains untethered from the reverse transcriptase (RT). The sPE showed similar efficiencies in installing precise edits as the parental unsplit PE3 and no increase in insertion-deletion (indel) byproducts. Delivery of sPE to the mouse liver with hydrodynamic injection to modify β-catenin drove tumor formation with similar efficiency as PE3. Delivery with two adeno-associated virus (AAV) vectors corrected the disease-causing mutation in a mouse model of type I tyrosinemia. Similarly, prime editing guide RNAs (pegRNAs) can be split into a single guide RNA (sgRNA) and a circular RNA RT template to increase flexibility and stability. Compared to previous sPEs, ours lacks inteins, protein-protein affinity modules and nuclease-sensitive pegRNA extensions, which increase construct complexity and might reduce efficiency. Our modular system will facilitate the delivery and optimization of PEs.

Clinical and biochemical footprints of inherited metabolic diseases. VIII. Neoplasias

Cancer, caused by multiple cumulative pathogenic variants in tumor suppressor genes and proto-oncogenes, is a leading cause of mortality worldwide. The uncontrolled and rapid cell growth of the tumors requires a reprogramming of the complex cellular metabolic network to favor anabolism. Adequate management and treatment of certain inherited metabolic diseases might prevent the development of certain neoplasias, such as hepatocellular carcinoma in tyrosinemia type 1 or hepatocellular adenomas in glycogen storage disorder type 1a. We reviewed and updated the list of known metabolic etiologies associated with various types of benign and malignant neoplasias, finding 64 relevant inborn errors of metabolism. This is the eighth article of the series attempting to create a comprehensive list of clinical and metabolic differential diagnosis by system involvement.

Oxidative Stress, Glutathione Metabolism, and Liver Regeneration Pathways Are Activated in Hereditary Tyrosinemia Type 1 Mice upon Short-Term Nitisinone Discontinuation

Hereditary tyrosinemia type 1 (HT1) is an inherited condition in which the body is unable to break down the amino acid tyrosine due to mutations in the fumarylacetoacetate hydrolase (FAH) gene, coding for the final enzyme of the tyrosine degradation pathway. As a consequence, HT1 patients accumulate toxic tyrosine derivatives causing severe liver damage. Since its introduction, the drug nitisinone (NTBC) has offered a life-saving treatment that inhibits the upstream enzyme 4-hydroxyphenylpyruvate dioxygenase (HPD), thereby preventing production of downstream toxic metabolites. However, HT1 patients under NTBC therapy remain unable to degrade tyrosine. To control the disease and side-effects of the drug, HT1 patients need to take NTBC as an adjunct to a lifelong tyrosine and phenylalanine restricted diet. As a consequence of this strict therapeutic regime, drug compliance issues can arise with significant influence on patient health. In this study, we investigated the molecular impact of short-term NTBC therapy discontinuation on liver tissue of Fah-deficient mice. We found that after seven days of NTBC withdrawal, molecular pathways related to oxidative stress, glutathione metabolism, and liver regeneration were mostly affected. More specifically, NRF2-mediated oxidative stress response and several toxicological gene classes related to reactive oxygen species metabolism were significantly modulated. We observed that the expression of several key glutathione metabolism related genes including Slc7a11 and Ggt1 was highly increased after short-term NTBC therapy deprivation. This stress response was associated with the transcriptional activation of several markers of liver progenitor cells including Atf3, Cyr61, Ddr1, Epcam, Elovl7, and Glis3, indicating a concreted activation of liver regeneration early after NTBC withdrawal.

Laboratory monitoring of patients with hereditary tyrosinemia type I

BACKGROUND

The prognosis of patients with Hereditary Tyrosinemia Type 1 (HT-1) has greatly improved with early detection through newborn screening and the introduction of nitisinone (NTBC) therapy. A recent guideline calls for periodic monitoring of biochemical markers and NTBC levels to tailor treatment; however, this is currently only achieved through a combination of clinical laboratory tests. We developed a multiplexed assay measuring relevant amino acids, succinylacetone (SUAC), and NTBC in dried blood spots (DBS) to facilitate treatment monitoring.

METHODS

Tyrosine, phenylalanine, methionine, NTBC and SUAC were eluted from DBS with methanol containing internal standards for each analyte and analyzed by liquid chromatography tandem mass spectrometry over 6.5 min in the multiple reaction monitoring positive mode.

RESULTS

Pre-analytical and analytical factors were studied and demonstrated a reliable assay. Chromatography resolved an unknown substance that falsely elevates SUAC concentrations and was present in all samples. To establish control and disease ranges, the method was applied to DBS collected from controls (n = 284) and affected patients before (n = 2) and after initiation of treatment (n = 29). In the treated patients SUAC concentrations were within the normal range over a wide range of NTBC levels.

CONCLUSIONS

This assay enables combined, accurate measurement of revelevant metabolites and NTBC in order to simplify treatment monitoring of patients with HT-1. In addition, the use of DBS allows for specimen collection at home to facilitate more standardization in relation to drug and dietary treatment.

Variant analysis of HPD genes from two families showing elevated tyrosine upon newborn screening by tandem mass spectrometry (MS/MS)

Background Alterations in the structure and activity of 4-hydroxyphenylpyruvate dioxygenase (HPD) are causally related to two different metabolic disorders: recessively inherited tyrosinemia type III and dominantly inherited hawkinsinuria. The aim of this study was to provide a new perspective for the clinical understanding of the pathogenesis of tyrosinemia type III or hawkinsinuria. Case presentation A full-term newborn baby born after a safe pregnancy and childbirth with a birth weight of 3200 g and another full-term baby born after a safe pregnancy and childbirth with a birth weight of 2800 g are reported and analysed. DNA extraction, next-generation sequencing, bioinformatics analysis, Sanger sequencing and biochemical analysis were performed. One patient with a heterozygous HPD gene (NM_002150.2) c.460G > A mutation and one patient with a heterozygous HPD gene (NM_002150.2) c.248delG mutation showing elevated tyrosine levels upon newborn screening by tandem mass spectrometry (MS/MS) are reported. Conclusions The HPD gene may not be a strictly autosomal recessive pathogenic gene, which provides a new perspective for the clinical understanding of the pathogenesis of tyrosinemia type III or hawkinsinuria.

Natural Protein Tolerance and Metabolic Control in Patients with Hereditary Tyrosinaemia Type 1

In a longitudinal retrospective study, we aimed to assess natural protein (NP) tolerance and metabolic control in a cohort of 20 Hereditary Tyrosinaemia type I (HTI) patients. Their median age was 12 years ([3.2-17.7 years], n = 11 female, n = 8 Caucasian, n = 8 Asian origin, n = 2 Arabic and n = 2 Indian). All were on nitisinone (NTBC) with a median dose of 0.7 g/kg/day (range 0.4-1.5 g/kg/day) and were prescribed a tyrosine (Tyr)/phenylalanine (Phe)-restricted diet supplemented with Tyr/Phe-free L-amino acids. Data were collected on clinical signs at presentation, medical history, annual dietary prescriptions, and blood Phe and Tyr levels from diagnosis until transition to the adult service (aged 16-18 years) or liver transplantation (if it preceded transition). The median age of diagnosis was 2 months (range: 0 to 24 months), with n = 1 diagnosed by newborn screening, n = 3 following phenylketonuria (PKU) screening and n = 7 by sibling screening. Five patients were transplanted (median age 6.3 years), and one died due to liver cancer. The median follow-up was 10 years (3-16 years), and daily prescribed NP intake increased from a median of 5 to 24 g/day. Lifetime median blood Tyr (370 µmol/L, range 280-420 µmol/L) and Phe (50 µmol/L, 45-70 µmol/L) were maintained within the target recommended ranges. This cohort of HTI patients were able to increase the daily NP intake with age while maintaining good metabolic control. Extra NP may improve lifelong adherence to the diet.

A Compensatory U1snRNA Partially Rescues FAH Splicing and Protein Expression in a Splicing-Defective Mouse Model of Tyrosinemia Type I

The elucidation of aberrant splicing mechanisms, frequently associated with disease has led to the development of RNA therapeutics based on the U1snRNA, which is involved in 5' splice site (5'ss) recognition. Studies in cellular models have demonstrated that engineered U1snRNAs can rescue different splicing mutation types. However, the assessment of their correction potential in vivo is limited by the scarcity of animal models with the targetable splicing defects. Here, we challenged the U1snRNA in the FAH5961SB mouse model of hepatic fumarylacetoacetate hydrolase (FAH) deficiency (Hereditary Tyrosinemia type I, HT1) due to the FAH c.706G>A splicing mutation. Through minigene expression studies we selected a compensatory U1snRNA (U1F) that was able to rescue this mutation. Intriguingly, adeno-associated virus-mediated delivery of U1F (AAV8-U1F), but not of U1wt, partially rescued FAH splicing in mouse hepatocytes. Consistently, FAH protein was detectable only in the liver of AAV8-U1F treated mice, which displayed a slightly prolonged survival. Moreover, RNA sequencing revealed the negligible impact of the U1F on the splicing profile and overall gene expression, thus pointing toward gene specificity. These data provide early in vivo proof-of-principle of the correction potential of compensatory U1snRNAs in HTI and encourage further optimization on a therapeutic perspective, and translation to other splicing-defective forms of metabolic diseases.

The Dynamic Chromatin Architecture of the Regenerating Liver

BACKGROUND & AIMS

The adult liver is the main detoxification organ and routinely is exposed to environmental insults but retains the ability to restore its mass and function upon tissue damage. However, extensive injury can lead to liver failure, and chronic injury causes fibrosis, cirrhosis, and hepatocellular carcinoma. Currently, the transcriptional regulation of organ repair in the adult liver is incompletely understood.

METHODS

We isolated nuclei from quiescent as well as repopulating hepatocytes in a mouse model of hereditary tyrosinemia, which recapitulates the injury and repopulation seen in toxic liver injury in human beings. We then performed the assay for transposase accessible chromatin with high-throughput sequencing specifically in repopulating hepatocytes to identify differentially accessible chromatin regions and nucleosome positioning. In addition, we used motif analysis to predict differential transcription factor occupancy and validated the in silico results with chromatin immunoprecipitation followed by sequencing for hepatocyte nuclear factor 4α (HNF4α) and CCCTC-binding factor (CTCF).

RESULTS

Chromatin accessibility in repopulating hepatocytes was increased in the regulatory regions of genes promoting proliferation and decreased in the regulatory regions of genes involved in metabolism. The epigenetic changes at promoters and liver enhancers correspond with the regulation of gene expression, with enhancers of many liver function genes showing a less accessible state during the regenerative process. Moreover, increased CTCF occupancy at promoters and decreased HNF4α binding at enhancers implicate these factors as key drivers of the transcriptomic changes in replicating hepatocytes that enable liver repopulation.

CONCLUSIONS

Our analysis of hepatocyte-specific epigenomic changes during liver repopulation identified CTCF and HNF4α as key regulators of hepatocyte proliferation and regulation of metabolic programs. Thus, liver repopulation in the setting of toxic injury makes use of both general transcription factors (CTCF) for promoter activation, and reduced binding by a hepatocyte-enriched factor (HNF4α) to temporarily limit enhancer activity. All sequencing data in this study were deposited to the Gene Expression Omnibus database and can be downloaded with accession number GSE109466.

[Screening for hereditary tyrosinemia and genotype analysis in newborns]

OBJECTIVE

To analyze the results of screening for hereditary tyrosinemia (HT) in newborns and its clinical features and genotype.

METHODS

The HT screening was conducted among 2 188 784 newborns from November 2013 to November 2018. The tyrosine (TYR)/ succinylacetone (SA) levels were detected by tandem mass spectrometry (MS-MS). The clinical characteristics, genetic results and following up data of identified patients were analyzed.

RESULTS

The normal ranges (0.5%-95.5%) of TYR and SA were 34.5-280.0 μmol/L and 0.16-2.58 μmol/L, respectively. Three HT cases were confirmed with a detection rate of 1∶729 595. There was 1 case of tyrosinemia type Ⅰ (HTⅠ) (homozygous variations of c.455G>A in FAH gene), 1 case of tyrosinemia type Ⅱ(HTⅡ) (heterozygous variations of c.890G>T and c.408+1G>A in TAT gene), and 1 case of tyrosinemia type Ⅲ (HT Ⅲ) (homozygous variations of c.257T>C in HPD gene). The variations of c.890G>T, c.4081G>A of TAT and c.257T>C of HPD were novel. The positive predictive value of the screening was 3.4%. Case 1 (HTⅠ) with TYR and SA values of 666.9 μmol/L and 3.87 μmol/L respectively, presented cholestasis, mild elevated of liver enzyme and lactic acid, who were although fed with TYR and phenylalanine free milk, but died at 2 months of age. Case 2 (HTⅡ) with higher TYR (625.6 μmol/L) and normal SA at screening, received medical milk treatment; during the 7 months of follow-up the baby showed normal score of Bayley assessment and normal TYR without eye and skin symptoms. Case 3 (HT Ⅲ) with TYR of 1035.3 μmol/L and normal SA at screening; during the 29 months of follow-up the value of TYR fluctuated from 532.1 μmol/L to 1060.3 μmol/L due to irregular medical milk treatment, while the score of Bayley assessment was normal.

CONCLUSIONS

HT is rare in the southern Chinese population, and the gene spectrum is scattered. Early treatment with nitisinone is recommended in children with HTⅠ, otherwise the prognosis is poor; the prognosis of children with HTⅡ is good when early treated with special diet; the prognosis of children with HTⅢ needs to be determined with more data.

Presence of three mutations in the fumarylacetoacetate hydrolase gene in a patient with atypical symptoms of hereditary tyrosinemia type I

Hereditary tyrosinemia type 1 (HT1), the most severe disease of the tyrosine catabolic pathway, is caused by a deficiency of fumarylacetoacetate hydrolase (FAH). More than 90 disease-causing variants have been identified in the fah gene. We investigated the molecular defect in a patient who presented atypical symptoms for the disease. No immunoreactive FAH was found in the liver and RNA analysis by RT-PCR suggested the presence of splicing mutations. Indeed, the patient was revealed to be a compound heterozygote for IVS6-1 g- > t and two new variants, namely p.V259L and p.G398E. Using splicing minigene constructs transfected in HeLa cells, the c.775G > C variant (p.V259L) was shown to affect partially exon 9 splicing thereby allowing the production of some full-length double-mutant FAH transcripts. The p.G398E variant had a major impact on enzyme activity, which was worsened by the p.V259L variant. Surprisingly, the double mutant protein was expressed to similar level as the wild-type protein upon transfection in HeLa cells but was absent in the patient liver extract, suggesting a higher propensity to be degraded in the hepatocellular context.

In vivo gene correction with targeted sequence substitution through microhomology-mediated end joining

Genome editing technology using programmable nucleases has rapidly evolved in recent years. The primary mechanism to achieve precise integration of a transgene is mainly based on homology-directed repair (HDR). However, an HDR-based genome-editing approach is less efficient than non-homologous end-joining (NHEJ). Recently, a microhomology-mediated end-joining (MMEJ)-based transgene integration approach was developed, showing feasibility both in vitro and in vivo. We expanded this method to achieve targeted sequence substitution (TSS) of mutated sequences with normal sequences using double-guide RNAs (gRNAs), and a donor template flanking the microhomologies and target sequence of the gRNAs in vitro and in vivo. Our method could realize more efficient sequence substitution than the HDR-based method in vitro using a reporter cell line, and led to the survival of a hereditary tyrosinemia mouse model in vivo. The proposed MMEJ-based TSS approach could provide a novel therapeutic strategy, in addition to HDR, to achieve gene correction from a mutated sequence to a normal sequence.

Abnormal social behavior in mice with tyrosinemia type I is associated with an increase of myelin in the cerebral cortex

Hereditary tyrosinemia type I (HT1) is caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene, the template for the final enzyme in the tyrosine catabolism pathway. If left untreated this deficiency of functional FAH leads to a buildup of toxic metabolites that can cause liver disease, kidney dysfunction and high mortality. The current treatment with the drug NTBC prevents the production of these metabolites and has consequently increased the survival rate in HT1 children. As a result of this increased survival, long term complications of HT1 are now being observed, including slower learning, impaired cognition and altered social behavior. We studied a mouse model of HT1 to gain insight into the effects of HT1 and treatment with NTBC on social behavior in mice. We showed that mice with HT1 display abnormal social behavior in that they spend more time in the absence of another mouse and do not discriminate between a novel mouse and an already familiar mouse. This altered behavior was due to HT1 and not treatment with NTBC. Quantification of cerebral cortex myelin in mice with HT1 showed a two to threefold increase in myelin expression. Our findings suggest that absence of FAH expression in the brain produces an altered brain biochemistry resulting in increased expression of myelin. This increase in myelination could lead to abnormal action potential velocity and altered neuronal connections that provide a mechanism for the altered learning, social behavior and cognitive issues recently seen in HT1.

Reprogramming metabolic pathways in vivo with CRISPR/Cas9 genome editing to treat hereditary tyrosinaemia

Many metabolic liver disorders are refractory to drug therapy and require orthotopic liver transplantation. Here we demonstrate a new strategy, which we call metabolic pathway reprogramming, to treat hereditary tyrosinaemia type I in mice; rather than edit the disease-causing gene, we delete a gene in a disease-associated pathway to render the phenotype benign. Using CRISPR/Cas9 in vivo, we convert hepatocytes from tyrosinaemia type I into the benign tyrosinaemia type III by deleting Hpd (hydroxyphenylpyruvate dioxigenase). Edited hepatocytes (Fah(-/-)/Hpd(-/-)) display a growth advantage over non-edited hepatocytes (Fah(-/-)/Hpd(+/+)) and, in some mice, almost completely replace them within 8 weeks. Hpd excision successfully reroutes tyrosine catabolism, leaving treated mice healthy and asymptomatic. Metabolic pathway reprogramming sidesteps potential difficulties associated with editing a critical disease-causing gene and can be explored as an option for treating other diseases.

Silent Tyrosinemia Type I Without Elevated Tyrosine or Succinylacetone Associated with Liver Cirrhosis and Hepatocellular Carcinoma

Tyrosinemia type I (TYRSN1, TYR I) is caused by fumarylacetoacetate hydrolase (FAH) deficiency and affects approximately one in 100,000 individuals worldwide. Pathogenic variants in FAH cause TYRSN1, which induces cirrhosis and can progress to hepatocellular carcinoma (HCC). TYRSN1 is characterized by the production of a pathognomonic metabolite, succinylacetone (SUAC) and is included in the Recommended Uniform Screening Panel for newborns. Treatment intervention is effective if initiated within the first month of life. Here, we describe a family with three affected children who developed HCC secondary to idiopathic hepatosplenomegaly and cirrhosis during infancy. Whole exome sequencing revealed a novel homozygous missense variant in FAH (Chr15(GRCh38):g.80162305A>G; NM_000137.2:c.424A > G; NP_000128.1:p.R142G). This novel variant involves the catalytic pocket of the enzyme, but does not result in increased SUAC or tyrosine, making the diagnosis of TYRSN1 problematic. Testing this novel variant using a rapid, in vivo somatic mouse model showed that this variant could not rescue FAH deficiency. In this case of atypical TYRSN1, we show how reliance on SUAC as a primary diagnostic test can be misleading in some patients with this disease. Augmentation of current screening for TYRSN1 with targeted sequencing of FAH is warranted in cases suggestive of the disorder.

Type 1 Tyrosinaemia

Tyrosinaemia type 1 (TYR1, OMIM# 276700) is a rare autosomal recessive disease that results from an enzyme defect that leads to a deficiency in fumarylacetoacetase (FAH)1. We present 3 cases of TYR1 in the Irish population over a 9 year period, the only cases known to have been diagnosed in Ireland since 1989. The common presenting symptom was hypoglycaemia and the diagnosis was made by the identification of the pathognomonic biomarker succinylacetone on urine organic acid analysis. We discuss the clinical presentation, biochemical and genetic results including one novel mutation. We also highlight the importance of early initiation of Nitisinone (NTBC), which reduces the complications of TYR1 and the incidence of liver transplantation in this population2.

Direct sequencing of FAH gene in Pakistani tyrosinemia type 1 families reveals a novel mutation

BACKGROUND

Hereditary tyrosinemia type 1 (HT1) is a rare inborn error of tyrosine catabolism with a worldwide prevalence of one out of 100,000 live births. HT1 is clinically characterized by hepatic and renal dysfunction resulting from the deficiency of fumarylacetoacetate hydrolase (FAH) enzyme, caused by recessive mutations in the FAH gene. We present here the first report on identification of FAH mutations in HT1 patients from Pakistan with a novel one.

METHODS

Three Pakistani families, each having one child affected with HT1, were enrolled over a period of 1.5 years. Two of the affected children had died as they were presented late with acute form. All regions of the FAH gene spanning exons and splicing sites were amplified by polymerase chain reaction (PCR) and mutation analysis was carried out by direct sequencing. Results of sequencing were confirmed by restriction fragment length polymorphism (PCR-RFLP) analysis.

RESULTS

Three different FAH mutations, one in each family, were found to co-segregate with the disease phenotype. Two of these FAH mutations have been known (c.192G>T and c.1062+5G>A [IVS12+5G>A]), while c.67T>C (p.Ser23Pro) was a novel mutation. The novel variant was not detected in any of 120 chromosomes from normal ethnically matched individuals.

CONCLUSIONS

Most of the HT1 patients die before they present to hospitals in Pakistan, as is indicated by enrollment of only three families in 1.5 years. Most of those with late clinical presentation do not survive due to delayed diagnosis followed by untimely treatment. This tragic condition advocates the establishment of expanded newborn screening program for HT1 within Pakistan.

A novel homozygous mutation causing hereditary tyrosinemia type I in yakut patient in russia: case report

INTRODUCTION

Tyrosinemia type 1 (HT1) (OM IM 276700) is an inborn error of tyrosine catabolism caused be fumarylacetoacetate hedralase deficiency (FAH). In tyrosinemia type I, dietary therapy and nitisinone (Orfandin®), liver transplantation are effective .

AIM

We present here the first report on identification of FAH mutation in HT1 Yakut patient from Russia with a novel one.

MATERIAL AND METHODS

The material for the clinical study is based on the genetic data of the patient card with tyrosinemia type 1, which is observed in the medical-genetic consultations Republican Hospital №1-National Medical Center of the Republic of Sakha (Yakutia). For molecular genetic analysis has been used venous whole blood, taken with the written consent from the patient, his relatives and 200 healthy Yakuts. All regions of the FAH gene spanning exons were amplified by PCR and mutational analyses was carried out by direct sequencing. Results of sequencing were confirmed by restriction fragment length polymorphism (PCR-RELF) analyses.

RESULTS

1 one-year-old child was identified with a diagnosis hereditary tyrosinemia type Ia, acute form. In exon 13 of the FAH gene a novel mutation c.1090 G>C (GLu364GLn) in the homozygous state was found in patient, and in heterozygous state in both parents. The child is treated Nitisinone therapy. DNA diagnostics of c.1090 G>C mutation frequency in the FAH gene was conducted using PCR and RFLP analysis in 200 unrelated Yakuts. The frequency of heterozygous carrier was 1.0%.

Hawkinsinuria in two unrelated Greek newborns: identification of a novel variant, biochemical findings and treatment

BACKGROUND

Hawkinsinuria is a rare inborn error of tyrosine metabolism.

OBJECTIVES

To study novel hawkinsinuria cases by monitoring their biochemical profile and conducting a mutation analysis.

SUBJECTS AND METHODS

Among 92,519 newborns that underwent expanded newborn screening, two unrelated cases with high tyrosine blood levels were further investigated by chromatographic techniques and via genetic testing for 4-hydroxyphenylpyruvate dioxygenase (HPD) gene.

RESULTS

Elevated levels were monitored for blood/plasma tyrosine and for the specific diagnostic markers in urine. The two newborns were put on a special low tyrosine diet. Till completion of the 1st year of their life, liver function tests and brain MRI were normal. The mutation A33T was identified in both cases, while one neonate carried an additional novel mutation of HPD gene (V212M).

CONCLUSIONS

Two mutations of HPD gene, A33T, which are associated with hawkinsinuria and a novel one (V212M) were detected for the 1st time in Greek newborns.

Clinical and Biochemical Profile of Tyrosinemia Type 1 in Tunisia

BACKGROUND

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease caused by a defect of fumarylacetoacetate hydrolase. This study aimed to estimate the prevalence of HT1 in Tunisia and report its clinical, biochemical and genetic features.

METHODS

During the last 25 years, 69 patients were diagnosed with HT1 based on clinical features and increased succinylacetone (SA) in blood and urine. SA was detected by GC-MS after oximation and quantified by a spectrophotometric method. Nine prenatal diagnoses for HT1 have been done and nine unrelated patients were screened for the hotspot IVS6-1(G-T) mutation using PCR.

RESULTS

Using the Hardy-Weinberg formula, the incidence of HT1 was estimated at 1/14804 births in Tunisia. According to clinical form, 21 patients (30%) had the acute form and 48 patients (70%) had the chronic form. Mean plasma and urine SA were higher in the acute form (24 and 193 μmol/L vs. 9 and 90 μmol/L, respectively). Diagnosis of HT1 was done for 4 fetuses. The hotspot IVS6-1(G-T) mutation was found in six of nine explored patients.

CONCLUSIONS

The incidence of HT1 is relatively high in Tunisia with a predominance of the chronic form. It is important to diagnose the disease as early as possible to prevent unfavorable issues. Prenatal diagnosis should be recommended to minimize the recurrence of the disease.

Outcome of children with hereditary tyrosinaemia following newborn screening

BACKGROUND

Nitisinone has transformed the management of hereditary tyrosinaemia type 1 (HT1). However, the risk of developing hepatocellular carcinoma is related to the age at which treatment is commenced. Little data on the outcome of children treated pre-emptively exist.

AIM

To describe the outcome of children with HT1 treated with nitisinone following selective newborn screening (NBS) and to compare their outcome with index siblings who had presented clinically.

SUBJECTS

12 children with HT1 were detected by NBS. Seven children were screened for HT1 because of an affected sibling (n=5). Four children were detected due to raised tyrosine concentrations on routine NBS and one child was born in a country with universal NBS for HT1.

OUTCOME

Nitisinone was commenced at 4 (1-52) days old. 6 children had an initial coagulopathy which resolved after 4 (1-7) days treatment. Currently at median age 8.5 (3-12.5) years all are clinically normal, with normal liver function tests and imaging. Those of school age are in normal classes but four have reported learning difficulties. Five index siblings presented clinically with acute liver failure (four) and chronic liver disease (one) at median 4 (1.5-17) months. One died of liver failure prior to nitisinone's availability. Four were treated with nitisinone; one failed to respond and underwent liver transplantation and three responded. One responder died from complications of prematurity and the remaining two have compensated liver disease.

SUMMARY

Children with HT1 treated with nitisinone following NBS have an excellent outcome.

CONCLUSIONS

Universal NBS for HT1 should be introduced in the UK.

Identification of a combined missense/splice-site mutation in FAH causing tyrosinemia type 1

Tyrosinemia type I (HT1) is a genetic metabolic disorder characterized by progressive liver disease, kidney disease, and rickets. The disease is caused by mutations in the FAH gene that results in deficiency of fumarylacetoacetase, an enzyme that is involved in the tyrosine degradation pathway. We investigated the clinical characteristics and molecular cause of HT1 in an affected family from Iran. Molecular analysis identified a homozygous combined missense (c.G1009G>A, p.Gly337Ser) and aberrant splicing mutation removing the first 50 nucleotides of exon 12. This mutation was only described in HT1 patients from Scandinavian countries and this is the first report from another population. Although failure to thrive is one of the typical features in HT1, our proband, similar to the reported Scandinavian patients, had normal growth and development. The results of this study have applications in patient screening and genetic counselling.

Two novel FAH gene mutations in a patient with hereditary tyrosinemia type I

BACKGROUND

Hereditary tyrosinemia type I (HT I) is a severe inborn metabolic disorder affecting the tyrosine degradation pathway. Most untreated patients die within the first two years of life. HT I results from fumarylacetoacetate hydrolase (FAH) deficiency caused by mutations in the FAH gene. The diagnosis of HT I is confirmed by measuring FAH enzyme activity in cultured fibroblasts or liver tissue and/or detecting disease-causing mutations in the FAH gene.

METHODS

A female neonate was referred to our hospital for further evaluation of an abnormal newborn screening test that showed elevated tyrosine levels. We analyzed amino acids and organic acids in the patient's blood and urine. To identify the genetic abnormality, all the coding exons and flanking introns of the FAH gene were analyzed via PCR.

RESULTS

A repeat newborn screening test and plasma amino acid analysis revealed increased tyrosine levels in the patient. Urine organic acid analysis showed increased urinary excretion of 4-hydroxyphenyllactate, 4-hydroxyphenylpyruvate, and succinylacetone. Sequence analysis of the FAH gene identified two novel variations (c.536A>G (p.Gln179Arg) and c.913+5G>A) that had not been previously reported and that were not found in 170 healthy controls.

CONCLUSIONS

HT I was confirmed in this patient by molecular genetic analysis of the FAH gene, with highly suggestive biochemical findings. The novel sequence variations detected in the present study should be considered disease-causing mutations by in silico analysis. In the Korean population, this is the first described case of HT I caused by a point mutation in the FAH gene.

The fate of tyrosinaemic Hungarian patients before the NTBC aera

Before the introduction of the NTBC treatment (Orfadine) from two tyrosinemic Hungarian families 1-3 tyrosinemic homozygous male patients died of hepatocellular carcinoma and one patient of hepatocellular carcinoma combined with clear cell renal adenocarcinoma. From the third tyrosinemic family one homozygous girl patient has been treated with NTBC (Orfadine), IMTV-AM, she is symptom-free. Her molecular genetic mutations analysis in the FAH gene detected a common intronel mutation, affecting splicing and of predicted severe effect, IVS6-1 g > t/IVS6-1 g > t with systemic name c.456-1 g > t/c.456-1 g > t (Prof. Magdalena Ugarte).

Fumarylacetoacetate inhibits the initial step of the base excision repair pathway: implication for the pathogenesis of tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is an autosomal recessive disease caused by a deficiency in human fumarylacetoacetate (FAA) hydrolase (FAH), which is the last enzyme in the catabolic pathway of tyrosine. Several reports suggest that intracellular accumulation of intermediates of tyrosine catabolism, such as FAA and succinylacetone (SA) is important for the pathogenesis in liver and kidney of HT1 patients. In this work, we examined the effect of FAA and SA on DNA glycosylases initiating base excision repair (BER), which is the most important pathway for removing mutagenic DNA base lesions. In vitro assays monitoring DNA glycosylase activities demonstrated that FAA but not SA inhibited base removal. In particular, the Neil1 and Neil2 DNA glycosylases were strongly inhibited, whereas inhibition of Nth1 and Ogg1 were less efficient. These DNA glycosylases initiate excision of a broad range of mutagenic oxidative base lesions. Further, FAA showed a modest inhibitory effect on the activity of the alkylbase DNA glycosylase Aag and no significant inhibition of the uracil DNA glycosylase Ung2. These data indicate that FAA inhibition of DNA glycosylases removing oxidative base lesions in HT1 patients may increase mutagenesis, suggesting an important mechanism for development of hepatocarcinoma and somatic mosaicism.

[Mutation analysis of FAH gene in patients with tyrosinemia type 1]

OBJECTIVE

To investigate the clinical features and mutations of the FAH gene.

METHOD

Clinical records of two cases were collected, and diagnosis was made according to the diagnostic criteria of the International Organization for Rare Disorders (NORD). Genomic DNA was extracted from peripheral blood leukocytes with QIAamp DNA Mini Kit. The DNA extracts were subjected to direct sequencing for 14 exons together with adjacent fragments of FAH gene using ABI Prism 3730 Genetic Analyzer (Applied Biosystems, Foster City, CA) after PCR based on genomic DNA. The mutation source was verified by analyzing parents' exons corresponding to patients' mutation exons. The homology between human FAH enzyme and that of other species was surveyed using software Clustal X(European Bioinformatics Institute, Hinxton, Saffron Walde, UK). Polyphen (Polymorphism Phenotyping), available online, were used to predict possible impact of an amino acid substitution on structure and function of FAH enzyme. Polyphen calculates position-specific independent counts (PISC) scores for two amino acid variants in polymorphic position. A PISC scores that differ by > 2 were regarded as indicating the probability of damaging variants.

RESULT

Patient 1 was a 5 months and 21 days-old boy who suffered from persistent diarrhea, hepatomegaly, ascites; Alpha-fetoprotein > 1210 µg/L, levels of tyrosine in blood and succinylacetone in urine were 110.8 µmol/L and 83.7 µmol/L. His sister suffered from tyrosinemia type 1. Direct sequencing showed a G to A transition in CDS position 455 and 1027. He was compound heterozygous for the mutation c.455G > A/c.1027G > A, which predicts a change from tryptophan to a stop codon (TGG > TAG) at position 152 (W152X) and a change from glycine to arginine (GGG > AGG) at position 343 respectively. Patient 2 was a 6 year and 1 month-old girl with late-onset rickets who had signs of hepatosplenomegaly, rachitic rosary, windswept knees. Hypophosphatemia and alkaline phosphatase 1620 IU/L were detected. Alpha-fetoprotein 412.8 µg/L, levels of tyrosine in blood and succinylacetone in urine were 835.8 µmol/L and 27.48 µmol/L. Rickets did not improve after administration of calcium and vitamine D3. She is homozygous for the mutation c.1027G > A/c.1027G > A, which predicts G343R. The parents were mutation carriers. Analysis by Clustal X on the alignment of amino acids residual reservation among different species showed that the locative amino acid was highly conserved. Polyphen software predicted G343R was probably damaging (PISC score 3.235).

CONCLUSION

Children with tyrosinemia type 1 can have manifestations of persistent diarrhea or late-onset rickets. Physical examination can reveal hepatosplenomegaly, laboratory tests indicate markedly elevated serum concentration of alpha-fetoprotein and alkaline phosphatase in plasma and succinylacetone in urine, other members in family may have tyrosinemias or parents are consanguineous. Mutations c.455G > A and c.1027G > A can be detected in FAH gene of Chinese children.

Tyrosinemia Type III detected via neonatal screening: management and outcome

Tyrosinemia Type III is caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), an enzyme involved in the catabolic pathway of tyrosine. To our knowledge, only a few patients presenting with this disease have been described in the literature, and the clinical phenotype remains variable and unclear. We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene. At the age of 30 months, the boy's outcome under mild protein restriction was characterized by normal growth and psychomotor development.

Compound mutations (R237X and L375P) in the fumarylacetoacetate hydrolase gene causing tyrosinemia type I in a Chinese patient

BACKGROUND

Mutations in fumarylacetoacetate hydrolase (FAH) gene can lead to tyrosinemia type 1 (HT1), a relatively rare autosomal recessive disorder. To date, no molecular genetic defects of HT1 in China have been described. We investigated a Chinese family with a HT1 child to identify mutations in FAH.

METHODS

DNA sequencing was used for mutations screening in FAH gene. Real-time polymerase chain reaction (PCR) was performed to determine the FAH gene expression level. To confirm the presence of degradation by the nonsense-mediated mRNA decay pathway (NMD), the fragments containing R237X mutations were analyzed by primer introduced restriction analysis-polymerase chain reaction (PIRA-PCR) and cDNA sequencing. Finally, the effects of the mutations reported in this study were predicted by online softwares.

RESULTS

A boy aged 3 years and 8 months was diagnosed clinically with HT1 based on his manifestations and biochemical abnormalities. Screening of FAH gene revealed two heterozygous mutations R237X and L375P transmitted from his mother and father respectively. In this pedigree, the amount of FAH mRNA relative to a healthy control was 0.44 for the patient, 0.77 for his mother and 1.07 for his father. Moreover, both PIRA-PCR and cDNA sequencing showed significant reduction of the FAH mRNA with R237X nonsense mutation. The missense mutation of L375P was not reported previously and prediction software showed that this mutation decreased the stability of protein structure and affected protein function.

CONCLUSIONS

This is the first case of HT1 analyzed by molecular genetics in China. The R237X mutation in FAH down- regulates the FAH gene expression, and the L375P mutation perhaps interrupts the secondary structure of FAH protein.

Point mutation instability (PIN) mutator phenotype as model for true back mutations seen in hereditary tyrosinemia type 1 - a hypothesis

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disorder affecting fumarylacetoacetate hydrolase (FAH), the last enzyme in the tyrosine catabolism pathway. The liver mosaicism observed in HT1 patients is due to the reversion to the wild type of one allele of the original point mutation in fah. It is generally accepted that these reversions are true back mutations; however, the mechanism is still unresolved. Previous reports excluded intragenic recombination, mitotic recombination, or homologous recombination with a pseudogene as possible mechanisms of mutation reversion in HT1. Sequence analysis did not reveal DNA motifs, tandem repeats or other sequence peculiarities that may be involved in mutation reversion. We propose the hypothesis that a point mutation instability mutator (PIN) phenotype brought about by the sustained stress environment created by the accumulating metabolites in the cell is the driver of the true back mutations in HT1. The metabolites accumulating in HT1 create a sustained stress environment by activating the extracellular signal-regulated kinase (ERK) and AKT survival pathways, inducing aberrant mitosis and development of death resistant cells, depleting glutathione, and impairing DNA ligase IV and possibly DNA polymerases δ and ε. This continual production of proliferative and stress-related survival signals in the cellular environment coupled with the mutagenicity of FAA, may instigate a mutator phenotype and could end in tumorigenesis and/or mutation reversion. The establishment of a PIN-mutator phenotype therefore not only seems to be a possible mechanism underlying the true back mutations, but also contributes to explaining the clinical heterogeneity seen in hereditary tyrosinemia type 1.

Expression and post-translational modification of human 4-hydroxy-phenylpyruvate dioxygenase

4-hydroxyphenylpyruvate dioxygenase (HPD) (EC 1.13.11.27) is a key enzyme involved in tyrosine catabolism. Congenital HPD deficiency is a rare, relatively benign condition known as hereditary type III tyrosinemia. The severe type I tyrosinemia, caused by a deficiency of fumarylacetoacetate hydrolase which functions downstream of HPD in the tyrosine degradation pathway, is often associated with decreased expression of HPD, and interestingly, inhibition of HPD activity seems to ameliorate the clinical symptoms of type I tyrosinemia. The HPD gene was previously mapped to the chromosomal region 12q24-->qter. In the present study high-resolution chromosome mapping localized the HPD gene to 12q24.31. DNase I footprinting, revealed that four regions of the HPD promoter were protected by rat liver nuclear proteins. Computer-assisted analyses suggested that these elements might bind Sp1/AP2, HNF4, HNF3/CREB, and C/EBP, respectively. In transient transfection experiments, the proximal 271bp of the promoter conferred basal transcriptional activation in human Chang cells. Sequences in intron 1 were able to enhance the activity of this basal promoter. Finally, vaccinia virus-based expression provided evidence that HPD is subject to phosphorylation, and furthermore, allowed mapping of the HPD protein in the human keratinocyte 2D database.

Identification of mutations causing hereditary tyrosinemia type I in patients of Middle Eastern origin

Hereditary Tyrosinemia Type 1 (HT1) is an autosomal recessive disorder resulting from a deficiency of fumarylacetoacetase caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene. We detected 11 novel and 6 previously described pathogenic mutations in a cohort of 43 patients originating from the Middle East with the acute form HT1. All of the mutations were homozygous and we did not find the presence of a "founder mutation".

A large TAT deletion in a tyrosinaemia type II patient

A girl, born to unrelated Spanish parents, presented at 6 months of age with photophobia, keratitis, palmar hyperkeratosis and high plasma tyrosine levels, indicative of tyrosinaemia type II. Analysis of the tyrosine aminotransferase (TAT) gene revealed a paternally inherited frameshift mutation c.1213delCinsAG at codon 405 causing a premature stop codon, and a maternally inherited deletion of 193kb encompassing the complete TAT gene and three neighbouring genes. This is the first complete TAT deletion in tyrosinaemia type II described so far.

Long-term outcome of living donor liver transplantation in a Thai boy with hereditary tyrosinemia type I: a case report

Hereditary tyrosinemia type I (HT-I) is an autosomal recessive inborn error of tyrosine metabolism, caused by mutation(s) in the gene encoding for fumarylacetoacetate hydrolase (FAH) enzyme. The authors report a Thai boy who presented at two months of age with liver failure. HT-I was diagnosed based on the presence of succinylacetone in urine and homozygous R237X mutations of FAH gene. He was started on tyrosine and phenylalanine restricted diet immediately. Due to a limitation of 2-(2-nitro-4-trifluoromethyl benzoyl)-1,3-cyclohexanedione (NTBC) therapy in Thailand, it was commenced at eight months old and used as a bridging therapy before liver transplantation. He had a good response to NTBC therapy with an improvement in liver chemistries and synthetic functions. Subsequently, living donor liver transplantation (LDLT) was performed at 15 months old Long-term follow-up for 6.3 years following LDLT revealed normal growth, good school performance, normal liver, renal tubular, and glomerular functions, and without urinary excretion of succinylacetone.

CONCLUSION

Liver transplantation is a promising treatment for patients with HT-1 when NTBC is unavailable, resulting in a good long-term outcome.

Generation of healthy mice from gene-corrected disease-specific induced pluripotent stem cells

Using the murine model of tyrosinemia type 1 (fumarylacetoacetate hydrolase [FAH] deficiency; FAH^−/− mice) as a paradigm for orphan disorders, such as hereditary metabolic liver diseases, we evaluated fibroblast-derived FAH^−/−-induced pluripotent stem cells (iPS cells) as targets for gene correction in combination with the tetraploid embryo complementation method. First, after characterizing the FAH^−/− iPS cell lines, we aggregated FAH^−/−-iPS cells with tetraploid embryos and obtained entirely FAH^−/−-iPS cell–derived mice that were viable and exhibited the phenotype of the founding FAH^−/− mice. Then, we transduced FAH cDNA into the FAH^−/−-iPS cells using a third-generation lentiviral vector to generate gene-corrected iPS cells. We could not detect any chromosomal alterations in these cells by high-resolution array CGH analysis, and after their aggregation with tetraploid embryos, we obtained fully iPS cell–derived healthy mice with an astonishing high efficiency for full-term development of up to 63.3%. The gene correction was validated functionally by the long-term survival and expansion of FAH-positive cells of these mice after withdrawal of the rescuing drug NTBC (2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione). Furthermore, our results demonstrate that both a liver-specific promoter (transthyretin, TTR)-driven FAH transgene and a strong viral promoter (from spleen focus-forming virus, SFFV)-driven FAH transgene rescued the FAH-deficiency phenotypes in the mice derived from the respective gene-corrected iPS cells. In conclusion, our data demonstrate that a lentiviral gene repair strategy does not abrogate the full pluripotent potential of fibroblast-derived iPS cells, and genetic manipulation of iPS cells in combination with tetraploid embryo aggregation provides a practical and rapid approach to evaluate the efficacy of gene correction of human diseases in mouse models.

Pluripotent stem cells have unlimited self-renewing capability and the potential to differentiate into virtually all cell types of the body. Pluripotent stem cells are therefore of great interest for future cell-based therapies and are already in use today for studying diseases “in a dish” and screening for new drugs. After the seminal discovery that induced pluripotent stem cells (iPS cells) can be generated by the delivery of four transcription factors into non-pluripotent cells, a tremendous amount of enthusiasm arose about the idea that patient-derived pluripotent stem cells could be obtained and genetically corrected in order to develop customized therapies for regenerative medicine. Here, we present a mouse model of acute metabolic liver failure that fulfills such criteria. First, we demonstrated by stringent assays that disease-specific iPS cells exhibited full cellular and developmental potential and the iPS cell–derived mice reproduced the phenotypes of the founding FAH^−/− mice faithfully. Then, we genetically repaired the disease-specific iPS cells by lentiviral delivery of an intact gene copy, and we investigated the impact of this additional genetic manipulation on these cells. With our analyses, we ruled out major, and even minor, chromosomal aberrations in the gene-corrected iPS cells. Most importantly, we demonstrated that the gene-corrected cells maintained their full potential and we generated viable mice that were completely derived from these repaired cells via tetraploid complementation approach, and these mice were healthy, without any signs of the metabolic liver disease.

Maternal and fetal tyrosinemia type I

A 22 year-old woman with tyrosinemia type I (HT1) married her first cousin who is heterozygous for the same FAH mutation for which the patient is homozygous. During her pregnancy she was treated with diet (prescribed tyrosine intake 300 mg/day), and nitisinone (60 mg/day). Median plasma tyrosine levels were 560 μmol/L (range: 375-838, n = 21) and nitisinone 51 μmol/L (range: 41-57, n = 3) during pregnancy. She gave birth to a clinically healthy girl affected with tyrosinemia type 1. Birth was normal (birth weight 2615 g) and the baby had normal liver function, normal plasma alpha-fetoprotein concentrations, low urinary excretion of phenolic acids and no detectable succinylacetone. At birth, the baby had hypertyrosinemia (860 μmol/L in blood cord) and nitisinone levels of 14 μmol/L. Following molecular confirmation of the diagnosis of HT1 specific treatment began on day 15 by which time she had detectable urinary succinylacetone.

Risk of HCC: genetic heterogeneity and complex genetics

Hepatocellular carcinoma (HCC) is a common form of cancer that arises from hepatocytes and whose risk may be affected by several known environmental factors, including hepatitis viruses, alcohol, cigarette smoking, and others. Rare monogenic syndromes, such as alpha1-antitrypsin deficiency, glycogen storage disease type I, hemochromatosis, acute intermittent and cutanea tarda porphyria, as well as hereditary tyrosinemia type I are associated with a high risk of HCC. Several common conditions or diseases inherited as polygenic traits e.g. autoimmune hepatitis, type 2 diabetes, a family history of HCC, hypothyroidism, and non-alcoholic steatohepatitis also show an increased risk of HCC compared to the general population. Overall, the genetic susceptibility to HCC is characterized by a genetic heterogeneity; a high individual risk of HCC may thus be caused by several unlinked single gene defects, whose carriers are rare in the general population, or by more common conditions inherited by complex genetics.

[Clinical, biochemical and molecular characteristics in 11 Czech children with tyrosinemia type I]

BACKGROUND

Hereditary tyrosinemia type 1 (HT1) is a rare autosomal recessive inborn error of metabolism caused by deficiency of fumarylacetoacetate hydrolase. HT1 manifests with severe liver and kidney impairment and associates with an increased risk of liver cancer development. The aim of our study is to present a detailed clinical picture and results of biochemical and molecular genetic analyses in 11 Czech patients with HT1 diagnosed in our clinic within 1982-2006.

METHODS AND RESULTS

In 9 patients the disease manifested between 1.5-7 months of age with refusal to eat, failure to thrive and vomiting. In 4 children HT1 progressed to acute liver failure. One clinically healthy boy was diagnosed because of affected sister. In one boy with liver cirrhosis the diagnosis was delayed until the age of 5.5 years. In all children the biochemical investigation showed elevated liver enzymes, alpha1-fetoprotein and hypophosphatemic rickets. Metabolic investigation revealed increased plasma tyrosine level, urinary excretion of succinylacetone and in 8 measured patients also increased urinary delta-aminolevulinic acid concentration. Three patients born before 1988 died due to liver cancer development (two of them) or liver failure. The average age of our 8 living patients is 10.7 +/- 8.3 years. Mutation analysis of FAH gene confirmed the HT1 in these patients and three novel mutations were found in FAH gene: c.579C>A, c.680G>T and c.1210G>A. Clinical status in six patients is favourable on strict low protein diet combined with Orfadin therapy. However, in two children despite of the maximal available therapy lasting 2 and 10 years resp., the disease progressed towards liver cancer development and necessity of liver transplantation.

CONCLUSIONS

Early diagnostics of HT1 as a part of extended newborn screening is the only possibility to further improve the prognosis of the patients. Moreover, available molecular-genetic analysis of the FAH gene enables prenatal diagnostics in affected families.

Tyrosinemia type 1 and Angelman syndrome due to paternal uniparental isodisomy 15

Uniparental isodisomy arises when an individual inherits two copies of a specific chromosome from a single parent, which can unmask a recessive mutation or cause a problem of genetic imprinting. Here we describe an exceptional case in which the patient simultaneously presents tyrosinemia type 1 and Angelman syndrome. The genetic studies showed that the patient presents paternal uniparental isodisomy of chromosome 15, with absence of the maternal homolog. As a consequence of this isodisomy, the patient is homozygous for the mutation IVS12+5G>A in the FAH gene, located in the chromosomal region 15q23-25, causing tyrosinemia type 1. The mutation was inherited from his father in double dosage, whereas the mother is not a carrier, which implies that the recurrence risk in the family is negligible. On the other hand, the lack of maternal contribution causes Angelman syndrome, a neurodevelopmental disorder associated with a loss of maternal gene expression in chromosome region 15q11-q13, and more specifically, of the UBE3A gene. This gene shows a tissue-specific imprinting, and only the maternally derived allele is expressed in certain areas of the brain. We observed through a literature review that uniparental disomy probably occurs more frequently than suspected, although it is more usually detected when the uniparental disomy implies the appearance of a disease because of the gene imprinting or by reduction to homozygosity of a recessive mutation. The conclusion is that uniparental disomy should always be considered when more than one genetic disease mapping to the same chromosome is present in a patient.

Loss of p21 permits carcinogenesis from chronically damaged liver and kidney epithelial cells despite unchecked apoptosis

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

The Caenorhabditis elegans K10C2.4 gene encodes a member of the fumarylacetoacetate hydrolase family: a Caenorhabditis elegans model of type I tyrosinemia

In eukaryotes and many bacteria, tyrosine is degraded to produce energy via a five-step tyrosine degradation pathway. Mutations affecting the tyrosine degradation pathway are also of medical importance as mutations affecting enzymes in the pathway are responsible for type I, type II, and type III tyrosinemia. The most severe of these is type I tyrosinemia, which is caused by mutations affecting the last enzyme in the pathway, fumarylacetoacetate hydrolase (FAH). So far, tyrosine degradation in the nematode Caenorhabditis elegans has not been studied; however, genes predicted to encode enzymes in this pathway have been identified in several microarray, proteomic, and RNA interference (RNAi) screens as perhaps being involved in aging and the control of protein folding. We sought to identify and characterize the genes in the worm tyrosine degradation pathway as an initial step in understanding these findings. Here we describe the characterization of the K10C2.4, which encodes a homolog of FAH. RNAi directed against K10C2.4 produces a lethal phenotype consisting of death in young adulthood, extensive damage to the intestine, impaired fertility, and activation of oxidative stress and endoplasmic stress response pathways. This phenotype is due to alterations in tyrosine metabolism as increases in dietary tyrosine enhance it, and inhibition of upstream enzymes in tyrosine degradation with RNAi or genetic mutations reduces the phenotype. We also use our model to identify genes that suppress the damage produced by K10C2.4 RNAi in a pilot genetic screen. Our results establish worms as a model for the study of type I tyrosinemia.