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BACKGROUND & AIMS Patient-derived human induced pluripotent stem cells (hiPSCs) differentiated into hepatocytes (hiPSC-Heps) have facilitated the study of rare genetic liver diseases. Here, we aimed to establish an in vitro liver disease model of the urea cycle disorder ornithine transcarbamylase deficiency (OTCD) using patient-derived hiPSC-Heps. APPROACH & RESULTS Before modeling OTCD, we addressed the question of why hiPSC-Heps generally secrete less urea than adult primary human hepatocytes (PHHs). Since hiPSC-Heps are not completely differentiated and maintain some characteristics of fetal PHHs, we compared gene expression levels in human fetal and adult liver tissue to identify genes responsible for reduced urea secretion in hiPSC-Heps. We found lack of aquaporin 9 (AQP9) expression in fetal liver tissue as well as in hiPSC-Heps, and showed that forced expression of AQP9 in hiPSC-Heps restores urea secretion and normalizes the response to ammonia challenge by increasing ureagenesis. Furthermore, we proved functional ureagenesis by challenging AQP9-expressing hiPSC-Heps with ammonium chloride labeled with the stable isotope [15 N] (15 NH4 Cl) and by assessing enrichment of [15 N]-labeled urea. Finally, using hiPSC-Heps derived from patients with OTCD, we generated a liver disease model that recapitulates the hepatic manifestation of the human disease. Restoring OTC expression-together with AQP9-was effective in fully correcting OTC activity and normalizing ureagenesis as assessed by 15 NH4 Cl stable-isotope challenge. CONCLUSION Our results identify a critical role for AQP9 in functional urea metabolism and establish the feasibility of in vitro modeling of OTCD with hiPSC-Heps. By facilitating studies of OTCD genotype/phenotype correlation and drug screens, our model has potential for improving the therapy of OTCD.

Inborn errors of metabolism are an important cause of non-communicable under-five childhood mortality. Lack of confirmatory ‘genomic’ results in the deceased index case due to unavailability of post-mortem biological samples, can pose challenges in reproductive counseling of the parents in future pregnancies. Our case describes a couple seeking preconception genetic counseling after they lost their previous child to biochemically diagnosed Citrullinemia type-1. We confirmed the genomic diagnosis of Citrullinemia type-1 through the post-mortem genetic analysis of the DNA retrieved from the preserved blood spots, 12-months later. Prenatal testing in the next pregnancy revealed the fetus to be a carrier for Citrullinemia type-1. This case report intends to raise the obstetricians’ and neonatologists’ awareness regarding DNA banking in fatal genetic disorders and the mandatory confirmatory genetic diagnosis for effective prenatal genetic counseling.

Despite biochemical and genetic testing being the golden standards for identification of proximal urea cycle disorders (UCDs), genotype-phenotype correlations are often unclear. Co-occurring partial defects affecting more than one gene have not been demonstrated so far in proximal UCDs. Here, we analyzed the mutational spectrum of 557 suspected proximal UCD individuals. We probed oligomerizing forms of NAGS, CPS1 and OTC, and evaluated the surface exposure of residues mutated in heterozygously affected individuals. BN-PAGE and gel-filtration chromatography were employed to discover protein-protein interactions within recombinant enzymes. From a total of 281 confirmed patients, only 15 were identified as “heterozygous-only” candidates (i.e. single defective allele). Within these cases, the only missense variants to potentially qualify as dominant negative triggers were CPS1 p.Gly401Arg and NAGS p.Thr181Ala and p.Tyr512Cys, as assessed by residue oligomerization capacity and surface exposure. However, all three candidates seem to participate in critical intramolecular functions, thus, unlikely to facilitate protein-protein interactions. This interpretation is further supported by BN-PAGE and gel-filtration analyses revealing no multiprotein proximal urea cycle complex formation. Collectively, genetic analysis, structural considerations and in vitro experiments point against a prominent role of dominant negative effects in human proximal UCDs.

Since 1972, eighteen patients (10 females/8 males) have been detected by newborn bloodspot screening (NBS) with neonatal-onset Maple Syrup Urine Disease (MSUD) in Ireland. Patients were stratified into three clusters according to clinical outcome at the time of data collection, including developmental, clinical and IQ data. A fourth cluster comprised of two early childhood deaths; a third patient died as an adult. We present neuroimaging and EEG together with clinical and biochemical data. Incidence of MSUD (1972-2018) was 1 in 147,975. Overall good clinical outcomes were achieved with 15/18 patients alive and with essentially normal functioning (with only the lowest performing cluster lying beyond a single standard deviation on their full scale intelligence quotient, FSIQ). Molecular genetic analysis revealed genotypes hitherto not reported, including a possible digenic inheritance state for the BCKDHA and DBT genes in one family. Treatment has been based on early implementation of emergency treatment, diet, close monitoring and even dialysis in the setting of acute metabolic decompensation. A plasma leucine ≥400 μmol/L (outside therapeutic range) was more frequently observed in infancy or during adolescence, possibly due to infections, hormonal changes or noncompliance. Children require careful management during metabolic decompensations in early childhood as this represented a key risk period in our cohort. A high level of metabolic control can be achieved through diet with early implementation of a 'sick day' regime and, in some cases, dialysis as a rescue therapy. The Irish cohort, despite largely classical phenotypes, achieved good outcomes in the NBS era, underlining the importance of early diagnosis and skilled multidisciplinary team (MDT) management. This article is protected by copyright. All rights reserved.

N-acetylglutamate synthase deficiency (NAGSD, MIM #237310) is an autosomal recessive urea cycle disorder caused either by decreased expression of the NAGS gene or defective NAGS enzyme resulting in decreased production of N-acetylglutamate (NAG), an allosteric activator of carbamylphosphate synthetase 1 (CPS1). NAGSD is the only urea cycle disorder that can be effectively treated with a single drug, N-carbamylglutamate (NCG), a stable NAG analog, which activates CPS1 to restore ureagenesis. We describe three patients with NAGSD due to four novel non-coding sequence variants in the NAGS regulatory regions. All three patients had hyperammonemia that resolved upon treatment with NCG. Sequence variants NM_153006.2:c.427-222G>A and NM_153006.2:c.427-218A>C reside in the 547 bp long first intron of NAGS and define a novel NAGS regulatory element that binds retinoic X receptor α. Sequence variants NC_000017.10:g.42078967A>T (NM_153006.2:c.-3065A>T) and NC_000017.10:g.42078934C>T (NM_153006.2:c.-3098C>T) reside in the NAGS enhancer, within known HNF1 and predicted glucocorticoid receptor binding sites, respectively. Reporter gene assays in HepG2 and HuH-7 cells demonstrated that all four substitutions could result in reduced expression of NAGS. These findings show that analyzing non-coding regions of NAGS and other urea cycle genes can reveal molecular causes of disease and identify novel regulators of ureagenesis. This article is protected by copyright. All rights reserved.

Loss of function of the urea cycle enzyme argininosuccinate lyase (ASL) is caused by mutations in the ASL gene leading to ASL deficiency (ASLD). ASLD has a broad clinical spectrum ranging from life-threatening severe neonatal to asymptomatic forms. Different levels of residual ASL activity probably contribute to the phenotypic variability but reliable expression systems allowing clinically useful conclusions are not yet available. In order to define the molecular characteristics underlying the phenotypic variability, we investigated all ASL mutations that were hitherto identified in patients with late onset or mild clinical and biochemical courses by ASL expression in human embryonic kidney 293 T cells. We found residual activities >3% of ASL wild type (WT) in nine of 11 ASL mutations. Six ASL mutations (p.Arg95Cys, p.Ile100Thr, p.Val178Met, p.Glu189Gly, p.Val335Leu, and p.Arg379Cys) with residual activities ≥16% of ASL WT showed no significant or less than twofold reduced Km values, but displayed thermal instability. Computational structural analysis supported the biochemical findings by revealing multiple effects including protein instability, disruption of ionic interactions and hydrogen bonds between residues in the monomeric form of the protein, and disruption of contacts between adjacent monomeric units in the ASL tetramer. These findings suggest that the clinical and biochemical course in variant forms of ASLD is associated with relevant residual levels of ASL activity as well as instability of mutant ASL proteins. Since about 30% of known ASLD genotypes are affected by mutations studied here, ASLD should be considered as a candidate for chaperone treatment to improve mutant protein stability.

Glutaric aciduria type I (GA-I, OMIM # 231670) is an inborn error of metabolism caused by a deficiency of glutaryl-CoA dehydrogenase (GCDH). Patients develop acute encephalopathic crises (AEC) with striatal injury most often triggered by catabolic stress. The pathophysiology of GA-I, particularly in brain, is still not fully understood. We generated the first knock-in rat model for GA-I by introduction of the mutation p.R411W, the rat sequence homologue of the most common Caucasian mutation p.R402W, into the Gcdh gene of Sprague Dawley rats by CRISPR/CAS9 technology. Homozygous Gcdhki/ki rats revealed a high excretor phenotype, but did not present any signs of AEC under normal diet (ND). Exposure to a high lysine diet (HLD, 4.7%) after weaning resulted in clinical and biochemical signs of AEC. A significant increase of plasmatic ammonium concentrations was found in Gcdhki/ki rats under HLD, accompanied by a decrease of urea concentrations and a concomitant increase of arginine excretion. This might indicate an inhibition of the urea cycle. Gcdhki/ki rats exposed to HLD showed highly diminished food intake resulting in severely decreased weight gain and moderate reduction of body mass index (BMI). This constellation suggests a loss of appetite. Under HLD, pipecolic acid increased significantly in cerebral and extra-cerebral liquids and tissues of Gcdhki/ki rats, but not in WT rats. It seems that Gcdhki/ki rats under HLD activate the pipecolate pathway for lysine degradation. Gcdhki/ki rat brains revealed depletion of free carnitine, microglial activation, astroglyosis, astrocytic death by apoptosis, increased vacuole numbers, impaired OXPHOS activities and neuronal damage. Under HLD, Gcdhki/ki rats showed imbalance of intra-and extracellular creatine concentrations and indirect signs of an intracerebral ammonium accumulation. We successfully created the first rat model for GA-I. Characterization of this Gcdhki/ki strain confirmed that it is a suitable model not only for the study of pathophysiological processes, but also for the development of new ther-apeutic interventions. We further brought up interesting new insights into the pathophysiology of GA-I in brain and periphery., (c) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Carbamoylphosphate synthetase 1 (CPS1) deficiency is a rare inborn error of metabolism leading often to neonatal onset hyperammonemia with coma and high mortality. The biochemical features of the disease are nonspecific and cannot distinguish this condition from other defects of the urea cycle, namely N‐acetylglutamate synthase deficiency. Therefore, molecular genetic investigation is required for confirmation of the disease, and nowadays this is done with increasing frequency applying next‐generation sequencing (NGS) techniques. Our laboratory has a long‐standing interest in CPS1 molecular genetic investigation and receives samples from centers in Europe and many other countries. We perform RNA‐based CPS1 molecular genetic investigation as first line investigation and wanted in this study to evaluate our experience with this approach as compared to NGS. In the past 15 years, 297 samples were analyzed, which were referred from 37 countries. CPS1 deficiency could be confirmed in 155 patients carrying 136 different genotypes with only a single mutation recurring more than two times. About 10% of the total 172 variants comprised complex changes (eg, intronic changes possibly affecting splicing, deletions, insertions, or deletions_insertions), which would have been partly missed if only NGS was done. Likewise, RNA analysis was crucial for correct interpretation of at least half of the complex mutations. This study gives highest sensitivity to RNA‐based CPS1 molecular genetic investigation and underlines that NGS should be done together with copy number variation analysis. We propose that unclear cases should be investigated by RNA sequencing in addition, if this method is not used as the initial diagnostic procedure.

Background Urea cycle disorders (UCDs) are inherited metabolic disorders that present with hyperammonemia, and cause significant mortality and morbidity in infants and children. These disorders are not well reported in the Indian population, due to lack of a thorough study of the clinical and molecular profile. Results We present data from two major metabolic centres in India, including 123 cases of various UCDs. The majority of them (72/123, 58%) presented in the neonatal period (before 30 days of age) with 88% on or before day 7 of life (classical presentation), and had a high mortality (64/72, 88%). Citrullinemia type 1 was the most common UCD, observed in 61/123 patients. Ornithine transcarbamylase (OTC) deficiency was the next most common, seen in 24 cases. Argininosuccinic aciduria was diagnosed in 20 cases. Deficiencies of arginase, N-acetylglutamate synthase, carbamoyl phosphate synthetase, citrin, and lysinuric protein intolerance were also observed. Molecular genetic analysis revealed two common ASS1 mutations: c.470G > A (p.Arg157His) and c.1168G > A (p.Gly390Arg) (36 of 55 tested patients). In addition, few recurrent point mutations in ASL gene, and a deletion of the whole OTC gene were also noted. A total of 24 novel mutations were observed in the various genes studied. We observed a poor clinical outcome with an overall all time mortality of 63% (70/110 cases with a known follow-up), and disability in 70% (28/40) among the survivors. Prenatal diagnosis was performed in 30 pregnancies in 25 families, including one pre-implantation genetic diagnosis. Conclusions We report the occurrence of UCDs in India and the spectrum that may be different from the rest of the world. Citrullinemia type 1 was the most common UCD observed in the cohort. Increasing awareness amongst clinicians will improve outcomes through early diagnosis and timely treatment. Genetic diagnosis in the proband will enable prenatal/pre-implantation diagnosis in subsequent pregnancies. Electronic supplementary material The online version of this article (10.1186/s13023-018-0908-1) contains supplementary material, which is available to authorized users.

The urea cycle disorder argininemia is caused by a defective arginase 1 (ARG1) enzyme resulting from mutations in the ARG1 gene. Patients generally develop hyperargininemia, spastic paraparesis, progressive neurological and intellectual impairment, and persistent growth retardation. Interestingly, in contrast to other urea cycle disorders, hyperammonemia is rare. We report here 66 mutations (12 of which are novel), including 30 missense mutations, seven nonsense, 10 splicing, 15 deletions, two duplications, one small insertion, and one translation initiation codon mutation. For the most common mutations (p.Thr134Ile, p.Gly235Arg and p.Arg21*), which cluster geographically in Brazil, China, or Turkey, a structural rationalization of their effect has been included. In order to gain more knowledge on the disease, we have collected clinical and biochemical information of 112 patients, including the patients' genetic background and ethnic origin. We have listed as well the missense variants with unknown relevance. For all missense variants (of both known and unknown relevance), the conservation, severity prediction, and ExAc scores have been included. Lastly, we review ARG1 regulation, animal models, diagnostic strategies, newborn screening, prenatal testing, and treatment options.

Citrullinemia type 1 is an autosomal recessive urea cycle disorder caused by defects in the argininosuccinate synthetase (ASS) enzyme due to mutations in ASS1 gene. An impairment of ASS function can lead to a wide spectrum of phenotypes, from life-threatening neonatal hyperammonemia to a later onset with mild symptoms, and even some asymptomatic patients exhibiting an only biochemical phenotype. The disease is panethnic. In this update, we report 137 mutations (64 of which are novel), consisting of 89 missense mutations, 19 nonsense mutations, 17 mutations that affect splicing, and 12 deletions. The change p.Gly390Arg is by far the most common mutation and is widely spread throughout the world. Other frequent mutations (p.Arg157His, p.Trp179Arg, p.Val263Met, p.Arg304Trp, p.Gly324Ser, p.Gly362Val, and p.Arg363Trp), each found in at least 12 independent families, are mainly carried by patients from the Indian subcontinent, Turkey, Germany, and Japan. To better understand the disease, we collected clinical data of >360 patients, including all published information available. This information is related to the patients' genetic background, the conservation of the mutated residues and a structural rationalization of the effect of the most frequent mutations. In addition, we review ASS regulation, animal models, diagnostic strategies, newborn screening, and treatment options.

The enzyme carbamoyl phosphate synthetase 1 (CPS1; EC 6.3.4.16) forms carbamoyl phosphate from bicarbonate, ammonia, and adenosine triphosphate (ATP) and is activated allosterically by N-acetylglutamate. The neonatal presentation of bi-allelic mutations of CPS1 results in hyperammonemia with reduced citrulline and is reported as the most challenging nitrogen metabolism disorder to treat. As therapeutic interventions are limited, patients often develop neurological injury or die from hyperammonemia. Survivors remain vulnerable to nitrogen overload, being at risk for repetitive neurological injury. With transgenic technology, our lab developed a constitutive Cps1 mutant mouse and reports its characterization herein. Within 24 hours of birth, all Cps1 $^{-/-}$ mice developed hyperammonemia and expired. No CPS1 protein by Western blot or immunostaining was detected in livers nor was Cps1 mRNA present. CPS1 enzymatic activity was markedly decreased in knockout livers and reduced in Cps1$^{+/-}$ mice. Plasma analysis found markedly reduced citrulline and arginine and markedly increased glutamine and alanine, both intermolecular carriers of nitrogen, along with elevated ammonia, taurine, and lysine. Derangements in multiple other amino acids were also detected. While hepatic amino acids also demonstrated markedly reduced citrulline, arginine, while decreased, was not statistically significant; alanine and lysine were markedly increased while glutamine was trending towards significance. In conclusion we have determined that this constitutive neonatal mouse model of CPS1 deficiency replicates the neonatal human phenotype and demonstrates the key biochemical features of the disorder. These mice will be integral for addressing the challenges of developing new therapeutic approaches for this, at present, poorly treated disorder.

A liver-humanized mouse model for CPS1-deficiency was generated by the high-level repopulation of the mouse liver with CPS1-deficient human hepatocytes. When compared with mice that are highly repopulated with CPS1-proficient human hepatocytes, mice that are repopulated with CPS1-deficient human hepatocytes exhibited characteristic symptoms of human CPS1 deficiency including an 80% reduction in CPS1 metabolic activity, delayed clearance of an ammonium chloride infusion, elevated glutamine and glutamate levels, and impaired metabolism of [15 N]ammonium chloride into urea, with no other obvious phenotypic differences. Because most metabolic liver diseases result from mutations that alter critical pathways in hepatocytes, a model that incorporates actual disease-affected, mutant human hepatocytes is useful for the investigation of the molecular, biochemical, and phenotypic differences induced by that mutation. The model is also expected to be useful for investigations of modified RNA, gene, and cellular and small molecule therapies for CPS1-deficiency. Liver-humanized models for this and other monogenic liver diseases afford the ability to assess the therapy on actual disease-affected human hepatocytes, in vivo, for long periods of time and will provide data that are highly relevant for investigations of the safety and efficacy of gene-editing technologies directed to human hepatocytes and the translation of gene-editing technology to the clinic.

Background Citrullinemia type 1 is an autosomal-recessive urea cycle disorder caused by mutations in the ASS1 gene and characterised by increased plasma citrulline concentrations. Of the ∼90 argininosuccinate synthetase (ASS) missense mutations reported, 21 map near the substrate (aspartate or citrulline) binding site, and thus are potential kinetic mutations whose decreased activities could be amenable to substrate supplementation. This article aims at characterising these 21 ASS mutations to prove their disease-causing role and to test substrate supplementation as a novel therapeutic approach. Methods We used an Escherichia coli expression system to study all potentially kinetic ASS mutations. All mutant enzymes were nickel-affinity purified, their activity and kinetic parameters were measured using tandem mass spectrometry and their thermal stability using differential scanning fluorimetry. Structural rationalisation of the effects of these mutations was performed. Results Of the characterised mutants, 13 were totally inactive while 8 exhibited decreased affinity for aspartate and citrulline. The activity of these eight kinetic mutations could be rescued to ∼10–99% of the wild-type using high l-aspartate concentrations. Conclusions Substrate supplementation raised in vitro the activity of eight citrullinemia type 1 mutations with reduced affinity for aspartate. As a direct translation of these results to the clinics, we propose to further evaluate the use of oxaloacetate, a nitrogen-free aspartate precursor and already available medical food (anti-ageing and brain stimulating, not considered as a drug by the US Food and Drug Administration), in patients with citrullinemia type 1 with decreased aspartate affinity. Although only patients with kinetic mutations would benefit, oxaloacetate could offer a safe novel treatment.

Four mitochondrial metabolic liver enzymes require bicarbonate which is provided by the carbonic anhydrase isoforms VA (CAVA) and VB (CAVB). Defective hepatic bicarbonate production leads to a unique combination of biochemical findings: hyperammonemia elevated lactate and ketone bodies metabolic acidosis hypoglycemia and excretion of carboxylase substrates. This study aimed to test for CAVA or CAVB deficiencies in a group of 96 patients with early onset hyperammonemia and to prove the disease causing role of the CAVA variants found. We performed CA5A and CA5B sequencing in the described cohort and developed an expression system using insect cells which enabled the characterization of wild type CAVA clinical mutations and three variants that affect functional residues. In 10 of 96 patients mutations in CA5A were identified on both alleles but none in CA5B. Exhibiting decreased enzyme activity or thermal stability all CAVA mutations were proven to cause disease whereas the three variants showed no relevant effect. CAVA deficiency is a differential diagnosis of early onset and life threatening metabolic crisis with hyperammonemia hyperlactatemia and ketonuria as apparently obligate signs. It seems to be more common than other rare metabolic diseases and early identification may allow specific treatment of hyperammonemia and ultimately prevent neurologic sequelae.Genet Med advance online publication 25 February 2016Genetics in Medicine (2016); doi:10.1038/gim.2015.201.

Gyrate atrophy (GA) of the choroid and retina is a rare autosomal recessive disorder that occurs due to deficiency of the mitochondrial enzyme ornithine aminotransferase (OAT). Hyperornithinemia causes degeneration of the retina with symptoms like myopia, reduced night vision and progressive vision loss. Our patient is a 10-year-old girl with impaired vision and strabismus. As part of the metabolic work-up, plasma amino acid analysis revealed significantly increased concentration of ornithine (1039 μmol/L ; reference interval 20 - 155 μmol/L). Molecular genetic analysis revealed homozygous mutation in exon 7 of the OAT gene that has not been reported previously (c.868_870delCTT p.(Leu290del)). This in frame deletion was predicted to be deleterious by in silico software analysis. Our patient was treated with pyridoxine (vitamin B6 in a dose of 2 x 100 mg/day), low-protein diet (0.6 g/kg/day) and L-lysine supplementation which resulted in a significant reduction in plasma ornithine concentrations to 53% of the initial concentration and the ophthalmologic findings showed significant improvement. We conclude that low protein diet and lysine supplementation can lead to long-term reduction in plasma ornithine concentrations and, if started at an early age, notably slow the progression of retinal function loss in patients with GA. The effect of therapy can be reliably monitored by periodical measurement of plasma ornithine concentration. To our knowledge, this is the first report of OAT deficiency in Croatia.

N-acetylglutamate synthase deficiency (NAGSD, MIM #237310) is an autosomal recessive disorder of the urea cycle that results from absent or decreased production of N-acetylglutamate (NAG) due to either decreased NAGS gene expression or defective NAGS enzyme. NAG is essential for the activity of carbamylphosphate synthetase 1 (CPS1), the first and rate-limiting enzyme of the urea cycle. NAGSD is the only urea cycle disorder that can be treated with a single drug, N-carbamylglutamate (NCG), which can activate CPS1 and completely restore ureagenesis in patients with NAGSD. We describe a novel sequence variant NM_153006.2:c.-3026C > T in the NAGS enhancer that was found in three patients from two families with NAGSD; two patients had hyperammonemia that resolved upon treatment with NCG, while the third patient increased dietary protein intake after initiation of NCG therapy. Two patients were homozygous for the variant while the third patient had the c.-3026C > T variant and a partial uniparental disomy that encompassed the NAGS gene on chromosome 17. The c.-3026C > T sequence variant affects a base pair that is highly conserved in vertebrates; the variant is predicted to be deleterious by several bioinformatics tools. Functional assays in cultured HepG2 cells demonstrated that the c.-3026C > T substitution could result in reduced expression of the NAGS gene. These findings underscore the importance of analyzing NAGS gene regulatory regions when looking for molecular causes of NAGSD.

Urea cycle disorders (UCDs) comprise a group of recessive and one X-linked inherited errors of protein metabolism that, due to insufficient detoxification of excess nitrogen, can lead to severe neurological disease. The key feature, but at the same time only a surrogate marker of UCDs, is the resulting mild to severe hyperammonemia. Biochemical analysis is needed to strengthen the suspicion of any underlying UCD but remains for the majority of cases rather indicative than diagnostic due to the lack of definite markers. Thus, in order to confirm a specific UCD, mutation analysis or enzyme assays are the methods of choice. Because of the drastic clinical complications of severe hyperammonemia, an early diagnosis before onset of symptoms would be desirable. The best way to achieve this would be to implement a general newborn screening for these disorders. However, there are several challenges that need to be overcome before newborn screening for UCDs can be introduced. This review will briefly describe the technical and clinical challenges involved in newborn screening for UCDs and will then discuss current experiences with this approach.

Liver is an attractive organ for gene delivery in order to correct various genetic (metabolic) diseases. Hydrodynamic vein injection of naked DNA/minicircles devoid of viral or plasmid backbones was demonstrated in, for example, murine phenylketonuria to allow sustained therapeutic transduction of hepatocytes. Here we show successful hepatocyte transfusion in domestic small pigs immediately after weaning upon portal vein catheterization and hydrodynamic injection of naked DNA/minicircle vectors expressing the luciferase gene from the CMV or a liver-specific promoter. First, we established a surgical method allowing hydrodynamic portal vein pressurization up to 120 mmHg and infusion of naked DNA in pigs (n = 5) with long-term survival. No acute adverse effects such as changes in liver transaminases or signs of liver cell damage were observed. We then showed efficiency of stable hepatocyte transfection at 10 and 28 days in single experiments (n = 7) where we found that up to 60% of samples (45/75) were polymerase chain reaction (PCR)-positive for minicircle-DNA. Of these samples, 13% of the positive specimen (6/45) showed low but stable luciferase expression when driven by a liver-specific promoter, as well as appropriate copy numbers per diploid genome. In conclusion, we accomplished a safe procedure for stable transfection of liver cells upon hydrodynamic gene delivery using minicircle vectors in small pigs as a prerequisite to potentially treat infants with genetic liver diseases.

BackgroundAutosomal recessive mutations in DNAJC12, encoding a cochaperone of HSP70 with hitherto unknown function, were recently described to lead to hyperphenylalaninemia, central monoamine neurotransmitter (dopamine and serotonin) deficiency, dystonia and intellectual disability in six subjects affected by homozygous variants.ObjectivePatients exhibiting hyperphenylalaninemia in whom deficiencies in hepatic phenylalanine hydroxylase and tetrahydrobiopterin cofactor metabolism had been excluded were subsequently analysed for DNAJC12 variants.MethodsTo analyse DNAJC12, genomic DNA from peripheral blood (Sanger sequencing), as well as quantitative messenger RNA (Real Time Quantitative Polymerase Chain Reaction (RT-qPCR)) and protein expression (Western blot) from primary skin fibroblasts were performed.ResultsWe describe five additional patients from three unrelated families with homozygosity/compound heterozygosity in DNAJC12 with three novel variants: c.85delC/p.Gln29Lysfs*38, c.596G>T/p.*199Leuext*42 and c.214C>T/p.(Arg72*). In contrast to previously reported DNAJC12-deficient patients, all five cases showed a very mild neurological phenotype. In two subjects, cerebrospinal fluid and primary skin fibroblasts were analysed showing similarly low 5-hydroxyindolacetic acid and homovanillic acid concentrations but more reduced expressions of mRNA and DNAJC12 compared with previously described patients. All patients responded to tetrahydrobiopterin challenge by lowering blood phenylalanine levels.ConclusionsDNAJC12 deficiency appears to result in a more heterogeneous neurological phenotype than originally described. While early identification and institution of treatment with tetrahydrobiopterin and neurotransmitter precursors is crucial to ensure optimal neurological outcome in DNAJC12-deficient patients with a severe phenotype, optimal treatment for patients with a milder phenotype remains to be defined.

Glutamine synthetase (GS) is a cytosolic enzyme that produces glutamine, the most abundant free amino acid in the human body. Glutamine is a major substrate for various metabolic pathways, and is thus an important factor for the functioning of many organs; therefore, deficiency of glutamine due to a defect in GS is incompatible with normal life. Mutations in the human GLUL gene (encoding for GS) can cause an ultra-rare recessive inborn error of metabolism—congenital glutamine synthetase deficiency. This disease was reported until now in only three unrelated patients, all of whom suffered from neonatal onset severe epileptic encephalopathy. The hallmark of GS deficiency in these patients was decreased levels of glutamine in body fluids, associated with chronic hyperammonemia. This review aims at recapitulating the clinical history of the three known patients with congenital GS deficiency and summarizes the findings from studies done along with the work-up of these patients. It is the aim of this paper to convince the reader that (i) this disorder is possibly underdiagnosed, since decreased concentrations of metabolites do not receive the attention they deserve; and (ii) early detection of GS deficiency may help to improve the outcome of patients who could be treated early with metabolites that are lacking in this condition.

Citrullinemia type 1 is an autosomal recessive urea cycle disorder caused by defects in the argininosuccinate synthetase (ASS) enzyme due to mutations in ASS1 gene. An impairment of ASS function can lead to a wide spectrum of phenotypes, from life-threatening neonatal hyperammonemia to a later onset with mild symptoms, and even some asymptomatic patients exhibiting an only biochemical phenotype. The disease is panethnic. In this update, we report 137 mutations (64 of which are novel), consisting of 89 missense mutations, 19 nonsense mutations, 17 mutations that affect splicing, and 12 deletions. The change p.Gly390Arg is by far the most common mutation and is widely spread throughout the world. Other frequent mutations (p.Arg157His, p.Trp179Arg, p.Val263Met, p.Arg304Trp, p.Gly324Ser, p.Gly362Val, and p.Arg363Trp), each found in at least 12 independent families, are mainly carried by patients from the Indian subcontinent, Turkey, Germany, and Japan. To better understand the disease, we collected clinical data of360 patients, including all published information available. This information is related to the patients' genetic background, the conservation of the mutated residues and a structural rationalization of the effect of the most frequent mutations. In addition, we review ASS regulation, animal models, diagnostic strategies, newborn screening, and treatment options.

INTRODUCTION Cysteamine is used to treat cystinosis via the modification of cysteine residues substituting arginine in mutant proteins. OBJECTIVES We investigated the effect of cysteamine on mutant argininosuccinate lyase (ASL), the second most common defect in the urea cycle. METHODS In an established mammalian expression system, 293T cell lysates were produced after transfection with all known cysteine for arginine mutations in the ASL gene (p.Arg94Cys, p.Arg95Cys, p.Arg168Cys, p.Arg379Cys, and p.Arg385Cys), allowing testing of the effect of cysteamine over 48 h in the culture medium as well as for 1 h immediately prior to the enzyme assay. RESULTS Cysteamine at low concentrations showed no effect on 293T cell viability, ASL protein expression, or ASL activity when applied during cell culture. However, incubation of transfected cells with 0.05 mM cysteamine immediately before the enzyme assay resulted in increased ASL activity of p.Arg94Cys, p.Arg379Cys, and p.Arg385Cys by 64, 20, and 197 %, respectively, and this result was significant (p < 0.01). Cell lysates carrying p.Arg385Cys and treated with cysteamine recover enzyme activity that is similar to the untreated designed mutation p.Arg385Lys, providing circumstantial evidence for the assumed cysteamine-induced change of a cysteine to a lysine analogue. CONCLUSION Since 12 % of all known genotypes in ASL deficiency are affected by a cysteine for arginine mutation, we conclude that the potential of cysteamine or of related substances as remedy for this disease should be investigated further.

Citrin deficiency is an autosomal recessive genetic disorder caused by a defect in the mitochondrial aspartate/glutamate antiporter, citrin. The disorder manifests either as neonatal intra-hepatic cholestasis or occurs in adulthood with recurrent hyperammonemia and neuropsychiatric disturbances. It has a high prevalence in the East Asian population, but is actually pan-ethnic. We report the case of a 26-year-old male patient presenting with episodes of abnormal neuro-psychiatric behavior associated with hyperammonemia, who was diagnosed to be having citrin deficiency. Sequencing of the SLC25A13 gene revealed two novel mutations, a single base pair deletion, c. 650delT (p.Phe217SerfsFNx0133) in exon 7, and a missense mutation, c. 869T>C (p.Ile290Thr) in exon 9. Confirmation of the diagnosis allowed establishment of the appropriate management. The latter is an essential pre-requisite for obtaining a good prognosis as well as for family counseling.

Non-viral and non-plasmid-based vectors that express a therapeutic protein from an episomal element have the potential of robust and sustained transgene expression and at the same time bear a very low risk of insertional mutagenesis. While hydrodynamic injection into the tail vein of mice to target the liver is an efficient but experimental approach, delivery of naked DNA/minicircle vectors into large animals and humans remains a challenge. Here we show successful hepatocyte transfection in domestic small pigs treated immediately after weaning with portal vein catheterization and hydrodynamic injection of naked DNA/minicircle vectors expressing the luciferase gene from a liver-specific promoter. We established a surgical method allowing hydrodynamic portal vein pressurization up to 90 mmHg and infusion of naked DNA in pigs with long-term survival. No acute adverse effects such as changes in liver transaminases or signs of liver cell damage were observed. Stable hepatocyte transfections at 10 and 28 days in single experiments were found in up to 60% of samples (45/75 were PCR-positive for minicircle-DNA) and 13% of the positive specimens (6/45) showed low but stable luciferase expression with up to two vector copies per diploid hepatocyte genome. While further optimization to enhance transfection efficiency and transgene expression is required, we conclude that hydrodynamic gene delivery using minicircle vectors in small pigs is a safe procedure for stable transfection of liver cells as a prerequisite to potentially treat infants with genetic liver diseases.

Fatal hyperammonemia secondary to chemotherapy for hematological malignancies or following bone marrow transplantation has been described in few patients so far. In these, the pathogenesis of hyperammonemia remained unclear and was suggested to be multifactorial. We observed severe hyperammonemia (maximum 475 μmol/L) in a 2-year-old male patient, who underwent high-dose chemotherapy with carboplatin, etoposide and melphalan, and autologous hematopoietic stem cell transplantation for a neuroblastoma stage IV. Despite intensive care treatment, hyperammonemia persisted and the patient died due to cerebral edema. The biochemical profile with elevations of ammonia and glutamine (maximum 1757 μmol/L) suggested urea cycle dysfunction. In liver homogenates, enzymatic activity and protein expression of the urea cycle enzyme carbamoyl phosphate synthetase 1 (CPS1) were virtually absent. However, no mutation was found in CPS1 cDNA from liver and CPS1 mRNA expression was only slightly decreased. We therefore hypothesized that the acute onset of hyperammonemia was due to an acquired, chemotherapy-induced (posttranscriptional) CPS1 deficiency. This was further supported by in vitro experiments in HepG2 cells treated with carboplatin and etoposide showing a dose-dependent decrease in CPS1 protein expression. Due to severe hyperlactatemia, we analysed oxidative phosphorylation complexes in liver tissue and found reduced activities of complexes I and V, which suggested a more general mitochondrial dysfunction. This study adds to the understanding of chemotherapy-induced hyperammonemia as drug-induced CPS1 deficiency is suggested. Moreover, we highlight the need for urgent diagnostic and therapeutic strategies addressing a possible secondary urea cycle failure in future patients with hyperammonemia during chemotherapy and stem cell transplantation.

The spf/ash mouse model of ornithine transcarbamylase (OTC) deficiency, a severe urea cycle disorder, is caused by a mutation (c.386G>A; p.R129H) in the last nucleotide of exon 4 of the Otc gene, affecting the 5' splice site and resulting in partial use of a cryptic splice site 48 bp into the adjacent intron. The equivalent nucleotide change and predicted amino acid change is found in OTC deficient patients. Here we have used liver tissue and minigene assays to dissect the transcriptional profile resulting from the >spf/ash> mutation in mice and man. For the mutant mouse, we confirmed liver transcripts corresponding to partial intron 4 retention by the use of the c.386+48 cryptic site and to normally spliced transcripts, with exon 4 always containing the c.386G>A (p.R129H) variant. In contrast, the OTC patient exhibited exon 4 skipping or c.386G>A (p.R129H)-variant exon 4 retention by using the natural or a cryptic splice site at nucleotide position c.386+4. The corresponding OTC tissue enzyme activities were between 3-6% of normal control in mouse and human liver. The use of the cryptic splice sites was reproduced in minigenes carrying murine or human mutant sequences. Some normally spliced transcripts could be detected in minigenes in both cases. Antisense oligonucleotides designed to block the murine cryptic +48 site were used in minigenes in an attempt to redirect splicing to the natural site. The results highlight the relevance of in depth investigations of the molecular mechanisms of splicing mutations and potential therapeutic approaches. Notably, they emphasize the fact that findings in animal models may not be applicable for human patients due to the different genomic context of the mutations., This work was supported by Grant SAF2010-17272 from Ministerio de Economia y Competitividad (to LRD), Institutional grant from Fundación Ramón Areces to the Centro de Biología Molecular Severo Ochoa, University fellowship (to AR), and a Postdoctoral fellowship from Centro de Diagnóstico de Enfermedades Moleculares (to RS).

Carbamoyl phosphate synthetase 1 (CPS1) deficiency due to CPS1 mutations is a rare autosomal-recessive urea cycle disorder causing hyperammonemia that can lead to death or severe neurological impairment. CPS1 catalyzes carbamoyl phosphate formation from ammonia, bicarbonate and two molecules of ATP, and requires the allosteric activator N-acetyl-L-glutamate. Clinical mutations occur in the entire CPS1 coding region, but mainly in single families, with little recurrence. We characterized here the only currently known recurrent CPS1 mutation, p.Val1013del, found in eleven unrelated patients of Turkish descent using recombinant His-tagged wild type or mutant CPS1 expressed in baculovirus/insect cell system. The global CPS1 reaction and the ATPase and ATP synthesis partial reactions that reflect, respectively, the bicarbonate and the carbamate phosphorylation steps, were assayed. We found that CPS1 wild type and V1013del mutant showed comparable expression levels and purity but the mutant CPS1 exhibited no significant residual activities. In the CPS1 structural model, V1013 belongs to a highly hydrophobic beta-strand at the middle of the central beta-sheet of the A subdomain of the carbamate phosphorylation domain and is close to the predicted carbamate tunnel that links both phosphorylation sites. Haplotype studies suggested that p.Val1013del is a founder mutation. In conclusion, the mutation p.V1013del inactivates CPS1 but does not render the enzyme grossly unstable or insoluble. Recurrence of this particular mutation in Turkish patients is likely due to a founder effect, which is consistent with the frequent consanguinity observed in the affected population. (C) 2014 Elsevier Inc All rights reserved.

Background Patients with autism spectrum disorder (ASD) may have low brain serotonin concentrations as reflected by the serotonin end-metabolite 5-hydroxyindolacetic acid (5HIAA) in cerebrospinal fluid (CSF). Methods We sequenced the candidate genes SLC6A4 (SERT), SLC29A4 (PMAT), and GCHFR (GFRP), followed by whole exome analysis. Results The known heterozygous p.Gly56Ala mutation in the SLC6A4 gene was equally found in the ASD and control populations. Using a genetic candidate gene approach, we identified, in 8 patients of a cohort of 248 with ASD, a high prevalence (3.2%) of three novel heterozygous non-synonymous mutations within the SLC29A4 plasma membrane monoamine transporter (PMAT) gene, c.86A > G (p.Asp29Gly) in two patients, c.412G > A (p.Ala138Thr) in five patients, and c.978 T > G (p.Asp326Glu) in one patient. Genome analysis of unaffected parents confirmed that these PMAT mutations were not de novo but inherited mutations. Upon analyzing over 15,000 normal control chromosomes, only SLC29A4 c.86A > G was found in 23 alleles (0.14%), while neither c.412G > A ( G (