Retrospective survey of urea cycle disorders: Part 2. Neurological outcome in forty-nine Japanese patients with urea cycle enzymopathies

The challenge of understanding and predicting phenotypic diversity in urea cycle disorders

The Urea Cycle Disorders Consortium (UCDC) and the European registry and network for Intoxication type Metabolic Diseases (E-IMD) are the worldwide largest databases for individuals with urea cycle disorders (UCDs) comprising longitudinal data from more than 1100 individuals with an overall long-term follow-up of approximately 25 years. However, heterogeneity of the clinical phenotype as well as different diagnostic and therapeutic strategies hamper our understanding on the predictors of phenotypic diversity and the impact of disease-immanent and interventional variables (e.g., diagnostic and therapeutic interventions) on the long-term outcome. A new strategy using combined and comparative data analyses helped overcome this challenge. This review presents the mechanisms and relevant principles that are necessary for the identification of meaningful clinical associations by combining data from different data sources, and serves as a blueprint for future analyses of rare disease registries.

Fifteen years of urea cycle disorders brain research: Looking back, looking forward

Urea cycle disorders (UCD) are inherited diseases resulting from deficiency in one of six enzymes or two carriers that are required to remove ammonia from the body. UCD may be associated with neurological damage encompassing a spectrum from asymptomatic/mild to severe encephalopathy, which results in most cases from Hyperammonemia (HA) and elevation of other neurotoxic intermediates of metabolism. Electroencephalography (EEG), Magnetic resonance imaging (MRI) and Proton Magnetic resonance spectroscopy (MRS) are noninvasive measures of brain function and structure that can be used during HA to guide management and provide prognostic information, in addition to being research tools to understand the pathophysiology of UCD associated brain injury. The Urea Cycle Rare disorders Consortium (UCDC) has been invested in research to understand the immediate and downstream effects of hyperammonemia (HA) on brain using electroencephalogram (EEG) and multimodal brain MRI to establish early patterns of brain injury and to track recovery and prognosis. This review highlights the evolving knowledge about the impact of UCD and HA in particular on neurological injury and recovery and use of EEG and MRI to study and evaluate prognostic factors for risk and recovery. It recognizes the work of others and discusses the UCDC's prior work and future research priorities.

Case Report: Juvenile Myelomonocytic Leukemia Underlying Ornithine Transcarbamylase Deficiency Safely Treated Using Hematopoietic Stem Cell Transplantation

BACKGROUND

Juvenile myelomonocytic leukemia (JMML), which is predominantly found in infants, is a clonal abnormality of pluripotent hematopoietic stem cells and presents with the symptoms of both myeloproliferative tumors and myelodysplastic syndromes. Estimates have shown that ~20 cases of JMML occur annually in Japan. Ornithine transcarbamylase deficiency (OTCD), the most common among all urea cycle disorders (UCDs), occurs in 1 of 80,000 people in Japan.

CASE PRESENTATION

A 10-month-old infant who had fever, vomiting, and diarrhea for 2 days was referred to our hospital for the following abnormalities in blood tests: white blood cell count, 48,200/μL; hemoglobin, 9.0 g/dL; and platelet count, 135,000/μL. Bone marrow examination showed a nucleated cell count of 396,000/mm³ and blast cell count of 5.0%, as well as decreased mature granulocyte count and slightly myeloperoxidase stain-negative blasts but no monoclonal cell proliferation on May-Giemsa staining. Colony assay showed the proliferation of spontaneous colony and high sensitivity to granulocyte-macrophage colony-stimulating factor. Genetic analysis of peripheral blood mononuclear cells showed that the patient was positive for neuroblastoma RAS (NRAS) mutation. The patient was ultimately diagnosed with JMML. Approximately 170 days after his first hematopoietic stem cell transplantation (HSCT), the patient's JMML relapsed. Shortly after the recurrence, nausea, vomiting, hyperventilation, and decreased vitality were observed, followed by a decrease in the level of consciousness. The patient's ammonia level was 472 μmol/L. A test for seven different genetic mutations for the UCD showed the presence of c. 119G>A (amino acid change p. Arg40His). As such, late-onset OTCD was added to his diagnosis. Administration of sodium phenylacetate, l-arginine hydrochloride, and carnitine was continued following the diagnosis of OTCD, after which hyperammonemia was not observed. Regarding JMML relapse, HSCT was performed on day 405 after the first transplantation.

CONCLUSION

Hyperammonemia should be considered a differential diagnosis when unexplained and non-specific symptoms occur during the treatment of hematologic malignancies. Patients should be tested for UCD as a cause of hyperammonemia, and treatment for hyperammonemia should be continued until the cause is identified. The patient shows normal developmental progress, has an intact neurological status, and has not experienced another hyperammonemia attack. His JMML has remained in remission for over 3 years.

Review of Multi-Modal Imaging in Urea Cycle Disorders: The Old, the New, the Borrowed, and the Blue

The urea cycle disorders (UCD) are rare genetic disorder due to a deficiency of one of six enzymes or two transport proteins that act to remove waste nitrogen in form of ammonia from the body. In this review, we focus on neuroimaging studies in OTCD and Arginase deficiency, two of the UCD we have extensively studied. Ornithine transcarbamylase deficiency (OTCD) is the most common of these, and X-linked. Hyperammonemia (HA) in OTCD is due to deficient protein handling. Cognitive impairments and neurobehavioral disorders have emerged as the major sequelae in Arginase deficiency and OTCD, especially in relation to executive function and working memory, impacting pre-frontal cortex (PFC). Clinical management focuses on neuroprotection from HA, as well as neurotoxicity from other known and yet unclassified metabolites. Prevention and mitigation of neurological injury is a major challenge and research focus. Given the impact of HA on neurocognitive function of UCD, neuroimaging modalities, especially multi-modality imaging platforms, can bring a wealth of information to understand the neurocognitive function and biomarkers. Such information can further improve clinical decision making, and result in better therapeutic interventions. In vivo investigations of the affected brain using multimodal neuroimaging combined with clinical and behavioral phenotyping hold promise. MR Spectroscopy has already proven as a tool to study biochemical aberrations such as elevated glutamine surrounding HA as well as to diagnose partial UCD. Functional Near Infrared Spectroscopy (fNIRS), which assesses local changes in cerebral hemodynamic levels of cortical regions, is emerging as a non-invasive technique and will serve as a surrogate to fMRI with better portability. Here we review two decades of our research using non-invasive imaging and how it has contributed to an understanding of the cognitive effects of this group of genetic conditions.

Early liver transplantation in neonatal-onset and moderate urea cycle disorders may lead to normal neurodevelopment

Urea cycle disorders (UCDs) are inherited metabolic diseases that lead to hyperammonemia. Neurodevelopmental outcomes of patients with UCDs depend on the maximum ammonia concentration (MAC) in the blood during onset. MAC ≥360 μM is a marker of poor neurodevelopmental outcomes. We investigated the neurodevelopmental outcomes and MAC at onset for 177 patients with UCDs in Japan (median age, 8 years and 2 months; range, 10 days-72 years), including 57 patients with male ornithine transcarbamylase (OTCD), 59 patients with female OTCD, 23 patients with carbamoyl-phosphate synthetase 1 deficiency (CPSD), 28 patients with arginosuccinate synthetase deficiency, 9 patients with arginosuccinate lyase deficiency (ALD), and 1 patient with arginase 1 deficiency. Neurodevelopmental outcomes of patients with CPSD and ALD were poor because most had neonatal onset with blood MAC ≥300 μM at onset. Although OTCD, particularly female late-onset OTCD, has good neurodevelopmental outcomes among those with UCDs, it is not necessarily a mild disease with good long-term outcomes. Patients with severe UCDs and MAC ≥300 μM at onset should undergo liver transplantation (LT). Moreover, this study suggested that if the onset of UCD began during the neonatal period, then even UCD patients with MAC <300 μM at onset should undergo LT to protect the brain.

Age at disease onset and peak ammonium level rather than interventional variables predict the neurological outcome in urea cycle disorders

BACKGROUND

Patients with urea cycle disorders (UCDs) have an increased risk of neurological disease manifestation.

AIMS

Determining the effect of diagnostic and therapeutic interventions on the neurological outcome.

METHODS

Evaluation of baseline, regular follow-up and emergency visits of 456 UCD patients prospectively followed between 2011 and 2015 by the E-IMD patient registry.

RESULTS

About two-thirds of UCD patients remained asymptomatic until age 12 days [i.e. the median age at diagnosis of patients identified by newborn screening (NBS)] suggesting a potential benefit of NBS. In fact, NBS lowered the age at diagnosis in patients with late onset of symptoms (>28 days), and a trend towards improved long-term neurological outcome was found for patients with argininosuccinate synthetase and lyase deficiency as well as argininemia identified by NBS. Three to 17 different drug combinations were used for maintenance therapy, but superiority of any single drug or specific drug combination above other combinations was not demonstrated. Importantly, non-interventional variables of disease severity, such as age at disease onset and peak ammonium level of the initial hyperammonemic crisis (cut-off level: 500 μmol/L) best predicted the neurological outcome.

CONCLUSIONS

Promising results of NBS for late onset UCD patients are reported and should be re-evaluated in a larger and more advanced age group. However, non-interventional variables affect the neurological outcome of UCD patients. Available evidence-based guideline recommendations are currently heterogeneously implemented into practice, leading to a high variability of drug combinations that hamper our understanding of optimised long-term and emergency treatment.

Advances in urea cycle neuroimaging: Proceedings from the 4th International Symposium on urea cycle disorders, Barcelona, Spain, September 2013

Our previous imaging research performed as part of a Urea Cycle Rare Disorders Consortium (UCRDC) grant, has identified specific biomarkers of neurologic injury in ornithine transcarbamylase deficiency, OTCD. While characterization of mutations can be achieved in most cases, this information does not necessarily predict the severity of the underlying neurological syndrome. The biochemical consequences of any mutation may be modified additionally by a large number of factors, including contributions of other enzymes and transport systems that mediate flux through the urea cycle, diet and other environmental factors. These factors likely vary from one patient to another, and they give rise to heterogeneity of clinical severity. Affected cognitive domains include non-verbal learning, fine motor processing, reaction time, visual memory, attention, and executive function. Deficits in these capacities may be seen in symptomatic patients, as well as asymptomatic carriers with normal IQ and correlate with variances in brain structure and function in these patients. Using neuroimaging we can identify biomarkers that reflect the downstream impact of UCDs on cognition. This manuscript is a summary of the presentation from the 4th International Consortium on urea cycle disorders held in, Barcelona, Spain, September 2, 2014.

Investigating neurological deficits in carriers and affected patients with ornithine transcarbamylase deficiency

BACKGROUND

Urea cycle disorders are caused by dysfunction in any of the six enzymes and two transport proteins involved in urea biosynthesis. Our study focuses on ornithine transcarbamylase deficiency (OTCD), an X-linked disorder that results in a dysfunctional mitochondrial enzyme, which prevents the synthesis of citrulline from carbamoyl phosphate and ornithine. This enzyme deficiency can lead to hyperammonemic episodes and severe cerebral edema. The objective of this study was to use a cognitive battery to expose the cognitive deficits in asymptomatic carriers of OTCD.

MATERIALS AND METHODS

In total, 81 participants were recruited as part of a larger urea cycle disorder imaging consortium study. There were 25 symptomatic participants (18 female, 7 male, 25.6 year s ± 12.72 years), 20 asymptomatic participants (20 female, 0 male, 37.6 years ± 15.19 years), and 36 healthy control participants (21 female, 15 male, 29.8 years ± 13.39 years). All participants gave informed consent to participate and were then given neurocognitive batteries with standard scores and T scores recorded.

RESULTS

When stratified by symptomatic participant, asymptomatic carrier, and control, the results showed significant differences in measures of executive function (e.g. CTMT and Stroop) and motor ability (Purdue Assembly) between all groups tested. Simple attention, academic measures, language and non-verbal motor abilities showed no significant differences between asymptomatic carriers and control participants, however, there were significant differences between symptomatic and control participant performance in these measures.

CONCLUSIONS

In our study, asymptomatic carriers of OTCD showed no significant differences in cognitive function compared to control participants until they were cognitively challenged with fine motor tasks, measures of executive function, and measures of cognitive flexibility. This suggests that cognitive dysfunction is best measurable in asymptomatic carriers after they are cognitively challenged.

Diagnosis and treatment of urea cycle disorder in Japan

Urea cycle disorder (UCD) is an inborn error of the metabolic pathway producing urea from ammonia, which occurs primarily in the liver. Decreased excretion of nitrogen in the urea cycle due to deficiency of carbamoyl phosphate synthase I (CPSI), ornithine transcarbamylase (OTC), argininosuccinate synthase (ASS), argininosuccinate lyase (ASL), and N-acetyl glutamate synthase (NAGS) causes hyperammonemia. We examined the clinical manifestations, treatment, and prognosis of 177 patients with UCD from January 1999 to March 2009 in Japan. Compared with a previous study conducted in Japan, a larger number of patients survived without mental retardation, even when the peak blood ammonia was >360 μmol/L. In those with peak blood ammonia >360 μmol/L, an indicator of poor prognosis, the frequency of convulsions, mental retardation, brain abnormality on magnetic resonance imaging, hemodialysis, liver transplantation, and intake of non-protein formulas was significantly higher than in those with peak blood ammonia <360 μmol/L. In this article, we have reported the current state of UCD to evaluate prognosis and its relationship with peak blood ammonia and hemodialysis.

Long-term outcome and intervention of urea cycle disorders in Japan

Urea cycle disorders (UCDs) are one of the most frequently inherited metabolic diseases in Japan, with an estimated prevalence of 1 per 50,000 live births. Here, we investigated the clinical manifestations, treatment, and prognosis of 177 patients with UCDs who were evaluated and treated from January 1999 to March 2009. These included 77 cases of neonatal-onset UCDs and 91 cases of late-onset UCDs. The most common UCD was ornithine transcarbamylase deficiency (OTCD), which accounted for 116 out of 177 patients. This result is similar to a previous study performed between 1978 and 1995 in Japan: OTCD accounted for about two-thirds of the total number of UCD cases. We studied the relationship between prognosis and the peak blood ammonia level at the onset in 151 UCD patients. Compared with a previous survey conducted in Japan, we found that a greater number of patients survived without any mental retardation despite their peak blood ammonia levels being greater than 360 μmol/l. The 5-year survival rate of patients with OTCD improved to 86% for those with the neonatal-onset type and to 92% for those with the late-onset type. We hypothesize that the increased survival rate is due to early diagnosis and better treatments that are now available in Japan. It is very important to diagnose and treat UCDs, especially OTCD, when the blood ammonia levels in patients are low. The outcome in patients with low blood ammonia levels was better than that in patients with high blood ammonia levels.

Current concepts in the pathogenesis of urea cycle disorders

The common feature of urea cycle diseases (UCD) is a defect in ammonium elimination in liver, leading to hyperammonemia. This excess of circulating ammonium eventually reaches the central nervous system, where the main toxic effects of ammonium occur. These are reversible or irreversible, depending on the age of onset as well as the duration and the level of ammonium exposure. The brain is much more susceptible to the deleterious effects of ammonium during development than in adulthood, and surviving UCD patients may develop cortical and basal ganglia hypodensities, cortical atrophy, white matter atrophy or hypomyelination and ventricular dilatation. While for a long time, the mechanisms leading to these irreversible effects of ammonium exposure on the brain remained poorly understood, these last few years have brought new data showing in particular that ammonium exposure alters several amino acid pathways and neurotransmitter systems, cerebral energy, nitric oxide synthesis, axonal and dendritic growth, signal transduction pathways, as well as K(+) and water channels. All these effects of ammonium on CNS may eventually lead to energy deficit, oxidative stress and cell death. Recent work also proposed neuroprotective strategies, such as the use of NMDA receptor antagonists, nitric oxide inhibitors, creatine and acetyl-l-carnitine, to counteract the toxic effects of ammonium. Better understanding the pathophysiology of ammonium toxicity to the brain under UCD will allow the development of new strategies for neuroprotection.

Ornithine transcarbamylase deficiency with persistent abnormality in cerebral glutamate metabolism in adults

PURPOSE

To determine cerebral glutamate turnover rate in partial-ornithine transcarbamylase deficiency (OTCD) patients by using carbon 13 ((13)C) magnetic resonance (MR) spectroscopy.

MATERIALS AND METHODS

The study was performed with approval of the institutional review board, in compliance with HIPAA regulations, and with written informed consent of the subjects. MR imaging, hydrogen 1 ((1)H) MR spectroscopy, and (13)C MR spectroscopy were performed at 1.5 T in 10 subjects, six patients with OTCD and four healthy control subjects, who were in stable condition. Each received intravenous (13)C-glucose (0.2 g/kg), C1 or C2 position, as a 15-minute bolus. Cerebral metabolites were determined with proton decoupling in a parieto-occipital region (n = 9) and without proton decoupling in a frontal region (n = 1) during 60-120 minutes.

RESULTS

Uptake and removal of cerebral glucose ([1-(13)C]-glucose or [2-(13)C]-glucose) were comparable in healthy control subjects and subjects with OTCD (P = .1). Glucose C1 was metabolized to glutamate C4 and glucose C2 was metabolized to glutamate C5 at comparable rates, both of which were significantly reduced in OTCD (combined, P = .04). No significant differences in glutamine formation were found in subjects with OTCD (P = .1). [2-(13)C]-glucose and its metabolic products were observed in anterior cingulate gyrus without proton decoupling in one subject with OTCD.

CONCLUSION

Treatments that improve cerebral glucose metabolism and glutamate neurotransmission may improve neurologic outcome in patients with OTCD, in whom prevention and treatment of hyperammonemic episodes appear to be insufficient.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

Hyperammonemia-induced toxicity for the developing central nervous system

In pediatric patients, hyperammonemia can be caused by various acquired or inherited disorders such as urea cycle deficiencies or organic acidemias. The brain is much more susceptible to the deleterious effects of ammonium during development than in adulthood. Hyperammonemia can provoke irreversible damages to the developing central nervous system that lead to cortical atrophy, ventricular enlargement and demyelination, responsible for cognitive impairment, seizures and cerebral palsy. Until recently, the mechanisms leading to these irreversible cerebral damages were poorly understood. Using experimental models allowing the analysis of the neurotoxic effects of ammonium on the developing brain, these last years have seen the emergence of new clues showing that ammonium exposure alters several amino acid pathways and neurotransmitter systems, as well as cerebral energy metabolism, nitric oxide synthesis, oxidative stress, mitochondrial permeability transition and signal transduction pathways. Those alterations may explain neuronal loss and impairment of axonal and dendritic growth observed in the different models of congenital hyperammonemia. Some neuroprotective strategies such as the potential use of NMDA receptor antagonists, nitric oxide inhibitors, creatine and acetyl-l-carnitine have been suggested to counteract these toxic effects. Unraveling the molecular mechanisms involved in the chain of events leading to neuronal dysfunction under hyperammonemia may be useful to develop new potential strategies for neuroprotection.

Survival after treatment with phenylacetate and benzoate for urea-cycle disorders

BACKGROUND

The combination of intravenous sodium phenylacetate and sodium benzoate has been shown to lower plasma ammonium levels and improve survival in small cohorts of patients with historically lethal urea-cycle enzyme defects.

METHODS

We report the results of a 25-year, open-label, uncontrolled study of sodium phenylacetate and sodium benzoate therapy (Ammonul, Ucyclyd Pharma) in 299 patients with urea-cycle disorders in whom there were 1181 episodes of acute hyperammonemia.

RESULTS

Overall survival was 84% (250 of 299 patients). Ninety-six percent of the patients survived episodes of hyperammonemia (1132 of 1181 episodes). Patients over 30 days of age were more likely than neonates to survive an episode (98% vs. 73%, P<0.001). Patients 12 or more years of age (93 patients), who had 437 episodes, were more likely than all younger patients to survive (99%, P<0.001). Eighty-one percent of patients who were comatose at admission survived. Patients less than 30 days of age with a peak ammonium level above 1000 micromol per liter (1804 microg per deciliter) were least likely to survive a hyperammonemic episode (38%, P<0.001). Dialysis was also used in 56 neonates during 60% of episodes and in 80 patients 30 days of age or older during 7% of episodes.

CONCLUSIONS

Prompt recognition of a urea-cycle disorder and treatment with both sodium phenylacetate and sodium benzoate, in conjunction with other therapies, such as intravenous arginine hydrochloride and the provision of adequate calories to prevent catabolism, effectively lower plasma ammonium levels and result in survival in the majority of patients. Hemodialysis may also be needed to control hyperammonemia, especially in neonates and older patients who do not have a response to intravenous sodium phenylacetate and sodium benzoate.

Impaired cognitive performance in ornithine transcarbamylase-deficient mice on arginine-free diet

Sparse-fur (spf) mice are a model for the congenital deficiency of ornithine transcarbamylase (OTC), the most common inborn error of urea synthesis in man. In this study, performance of clinically stable spf and control mice (8-10-weeks-old) on two learning tests was assessed under normal Arg(+) or arginine-free Arg(-) diet conditions. Used as an indicator of the metabolic status of the animals, plasma ammonia concentrations were significantly higher in spf than in controls on normal diet, and increased even more during the Arg(-) diet episode. Behaviourally, we found no difference in passive avoidance learning between control and spf mice on Arg(+) diet, whereas in spf mice receiving Arg(-) diet during training, retention performance was significantly reduced. In the hidden-platform water maze, spf mice on Arg(+) diet only showed decreased swimming velocity compared to controls. In mice on Arg(-) diet during the first week of acquisition training, performance on acquisition and retention (probe) trials showed that spf mice experienced more difficulties in actually locating the platform. Visible-platform control experiments only showed a reduction in swimming velocity in spf mice on either diet. We conclude that cognitive performance is impaired in spf mice as a consequence of Arg(-) diet-induced neurochemical alterations.

Correction of ureagenesis after gene transfer in an animal model and after liver transplantation in humans with ornithine transcarbamylase deficiency

We report effects of gene transfer and liver transplantation on urea synthesis in ornithine transcarbamylase deficiency (OTCD). We measured the formation of [15N] urea after oral administration of 15NH4Cl in two girls with partial OTCD before and after liver transplantation. Ureagenesis was less than 20% of that observed in controls before transplantation, and was normalized afterward. Studies performed on the OTCD sparse fur (spf/Y) mouse showed discordance between OTC enzyme activity and ureagenesis with modest increases in OTC enzyme activity after gene transfer resulting in significant improvement in ureagenesis. This study suggests that both liver transplantation and gene therapy may be effective in improving ureagenesis in OTCD.

Developing adenoviral-mediated in vivo gene therapy for ornithine transcarbamylase deficiency

There are a number of reasons for choosing ornithine transcarbamylase (OTC) deficiency as a candidate for gene therapy: the gene has been cloned; the disorder is relatively common; the current clinical outcome is poor; and there are authentic animal models. In considering the development of gene therapy for OTC deficiency, we focused on the use of in vivo gene therapy with an adenoviral vector. Using the partially OTC-deficient sparse fur mouse we found transduction and expression could be achieved using an intravenous infusion of a recombinant adenovirus containing the OTC cDNA. The results were transient as a result of immune activation in response to the vector and vector-transduced cells. By modifying the adenoviral construct, creating an E1 deletion-E2 temperature-sensitive mutation, we blunted the cytotoxic T lymphocyte immune response and achieved correction of biochemical abnormalities for 2-3 months. We also found that transduction and expression following gene transfer occurred sufficiently rapidly to protect against acute hyperammonaemia within 24 h. Subsequent preclinical studies in mice and non-human primates demonstrated that E1-E4-deleted vectors had a substantially improved safety profile and similar efficacy. With this evidence of efficacy and safety of adenoviral vectors, we are embarking on a phase I trial of intravascular gene transfer using an E1-E4-deleted vector in adults with partial OTC deficiency.

Neurodevelopmental outcome of long-term therapy of urea cycle disorders in Japan

In Japan, urea cycle disorders (UCDs) are one of the most frequent inborn errors of metabolism, estimated to have a prevalence of 1 per 50,000 live births. In an attempt to develop more effective treatment and enhance the quality of life, we investigated the clinical manifestations and prognosis of 216 patients with UCDs diagnosed and treated between 1978 and 1995. These included 92 cases of neonatal-onset UCD and 116 of late-onset UCD. Two cases of ornithine transcarbamylase (OTC) deficiency in males and 2 cases of argininosuccinase (AL) deficiency were diagnosed prospectively. By far the most common disorder was OTC deficiency, accounting for 2/3 of all cases. At the end of 1995, the 5-year survival rate was 22% for the neonatal-onset type and 41% for the late-onset type. Among the 20 long-term survivors with neonatal-onset UCD, 18 (90%) had moderate to severe neurodevelopmental deficits; this contrasts with 13 of 47 (28%) survivors with the late-onset type. In analysing 108 UCD cases, peak blood ammonia level during the first hyperammonaemic attack was correlated with neurodevelopmental outcome. When the concentration of blood ammonia was less than 180 mumol/L (5 times normal), there was no severe neurological damage. When the concentration of blood ammonia exceeded 350 mumol/L (10 times normal) at the first hyperammonaemic attack, the patients died or had severe neurological deficits. Our data point to the importance of early diagnosis and aggressive treatment.

Adenovirus-mediated in vivo gene transfer rapidly protects ornithine transcarbamylase-deficient mice from an ammonium challenge

The purpose of this study was to determine the time of onset, duration, and the efficacy of in vivo gene transfer in protecting the ornithine transcarbamylase deficient spf/Y mouse from an acute ammonium challenge. The animals were challenged with ammonia (10 mmol/kg NH4Cl) 1, 2, 7, 14, or 28 d after the administration of a recombinant adenoviral construct deleted in E1 and with a temperature sensitive mutation in E2. Although there was no protection with the control LacZ virus, the ornithine transcarbamylase (OTC)-containing vector provided partial protection from both behavioral symptoms (ataxia, seizures, and abnormal response to sound) and biochemical abnormalities (ammonium, aspartate, alanine, and glutamine) within 24 h and complete protection by 48 h. Mortality was also decreased. Animals receiving the vector 7 and 14 d before the ammonium load were also protected, whereas those treated 28 d before the challenge were not. OTC enzyme activity in liver of untreated spf/Y mice was 5% of control C3H mice. After gene transfer, activity was increased to near control levels through 14 d but had returned to baseline by 28 d. These studies indicate that adenovirus-mediated gene transfer confers a metabolic benefit within 24 h of administration and provides protection against an acute metabolic insult for at least 2 wk.

Phenotypic variability in male patients carrying the mutant ornithine transcarbamylase (OTC) allele, Arg40His, ranging from a child with an unfavourable prognosis to an asymptomatic older adult

In five different Japanese families, we identified six male hemizygotes (aged 6, 9, 15, 17, 56, and 65 years) and a putative candidate (aged 48 years), carrying a mutant allele of the ornithine transcarbamylase (OTC) gene, a G to A substitution at nucleotide 119 in exon 2 generating histidine in place of arginine. OTC activity in the necropsied liver tissue was reduced to approximately 12% of the control and that of COS 1 cells transfected with Arg40His OTC cDNA was 10.2 +/- 1.8% of the control transfected with wild type OTC cDNA. Clinical features ranged from death during a hyperammonaemic attack (a 9 year old) to a 65 year old asymptomatic man. We consider that the amount of protein ingested by these subjects may be one predisposing factor leading to the manifestation of this disease.

Correction of ornithine transcarbamylase deficiency in adult spf(ash) mice and in OTC-deficient human hepatocytes with recombinant adenoviruses bearing the CAG promoter

Ornithine transcarbamylase (OTC) deficiency, the most common and severe inborn error of the urea cycle in humans, remains without adequate treatment, and mortality rates are high. Adenoviral vectors provide an efficient system for gene delivery, but there are problems, including toxicity. Efficient promoters that reduce the amount of vector required for treatment need to be developed. We constructed two recombinant adenoviral vectors, AdexCAGhOTC and AdexSR alpha hOTC, which harbor the human OTC gene under transcriptional control of CAG (a modified chicken beta-actin promoter with CMV-IE enhancer) and SR alpha (the SV40 early promoter with the R segment and part of the US segment of the HTLV-1 LTR), respectively. Each was tested in adult spf(ash) mice, an animal model of human OTC deficiency, and in primary human hepatocytes with OTC deficiency. Spf(ash) mice have a pronounced orotic aciduria as seen in humans. A complete recovery of hepatic OTC activity with minimal tissue damage was observed in these animals following the intravenous administration of AdexCAGhOTC alone. Western blot analysis confirmed hepatic OTC expression and normalization of orotic aciduria was evident for 60 days. Enzyme activities of primary human hepatocytes infected with AdexCAGhOTC were 10-40 times higher than those with AdexSR alpha hOTC. Thus, the adenoviral vector with an efficient promoter such as CAG, can be given further consideration for possible gene therapy in humans with OTC deficiency.

Gene therapy for ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency in humans is the most common and severe inborn error of the urea cycle. Despite therapeutic advances, OTC deficiency remains without adequate treatment, hence mortality rates are high. In the two available strains of OTC-deficient murine models, spf and spfash, researchers have tried to make genetic corrections by introducing the OTC gene. Transient but complete recovery of OTC was obtained in adult spfash mice and in OTC-deficient human primary hepatocytes, using a recombinant adenoviral vector. These experiments represent a first step in the development of human gene therapy for OTC deficiency and other hepatic enzyme deficiencies.

Inborn errors of urea synthesis

Inborn errors of urea synthesis can present in the newborn period as a catastrophic illness or later in childhood or adulthood with an indolent course punctuated by hyperammonemic episodes. Because symptoms mimic other neuropsychiatric disorders, it is common for there to be a delay in diagnosis, often with dire consequences. Diagnosis relies on the combination of clinical suspicion and the measurement of ammonium, lactate, and amino acids in plasma and organic acids and orotic acid in urine. Treatment involves nitrogen restriction combined with the stimulation of alternate pathways of waste nitrogen excretion. More recently liver transplantation has been performed as enzyme replacement therapy. The outcome is poor in children who survive prolonged neonatal hyperammonemic coma, with most manifesting developmental disabilities. The etiology of neuronal injury in this disorder is unclear but may involve some combination of ammonia/amino acid accumulation, neurotransmitter alterations, and excitotoxic injury. Gene therapy holds the promise of improved treatment in the future.

Four novel gene mutations in five Japanese male patients with neonatal or late onset OTC deficiency: application of PCR-single-strand conformation polymorphisms for all exons and adjacent introns [corrected]

Ornithine transcarbamylase deficiency (OTC), the most common inborn error of the urea cycle, shows an X-linked inheritance with frequent new mutations. Southern blots reveal only a small percent of the mutation, but amplification of cDNA or genomic DNA using the polymerase chain reaction (PCR) followed by DNA sequencing, has contributed greatly to overcoming this difficulty. Problems remaining are the limited availability of fresh liver samples for preparation of intact mRNA in the former case, and there are primer sequences for PCR for only some exons in the latter case. Here, we report the structures of intron sequences which are long enough to analyze all exons and adjacent introns of the OTC gene using PCR and PCR single-strand conformation polymorphisms (PCR-SSCP). We carried out a DNA analysis of findings in five Japanese male patients with neonatal or late onset form. Five patients had mutations in the protein coding region. C to G (S192R), A to T (D196V), A to G (T264A), T to C (M268T), and C to T (R277W) substitutions. The first four of these were novel missense mutations and the presence of the mutation was confirmed in the corresponding families.

Ornithine transcarbamylase deficiency presenting with strokelike episodes

A girl with ornithine transcarbamylase deficiency had a history of recurrent strokelike episodes. The differential diagnosis of unexplained stroke should include primary urea cycle defects.

Prenatal monitoring of ornithine transcarbamoylase deficiency in two families by DNA analysis

We examined the DNA in two families with ornithine transcarbamoylase (OTC) deficiency. Two point mutations of the OTC gene, a C-to-T (codon 141) and a G-to-A (codon 141), were identified. This allowed prenatal monitoring to be made for two fetuses in each family, using polymerase chain reaction (PCR), followed by allele-specific oligonucleotide hybridization or TaqI digestion of amplified sequence. The diagnoses showed heterozygotes of a wild type gene and the corresponding mutant gene in these fetuses; each was confirmed postnatally.