Late onset ornithine carbamoyl transferase deficiency in males

Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision

In 2012, we published guidelines summarizing and evaluating late 2011 evidence for diagnosis and therapy of urea cycle disorders (UCDs). With 1:35 000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist. In the 7 years that have elapsed since the first guideline was published, abundant novel information has accumulated, experience on newborn screening for some UCDs has widened, a novel hyperammonemia-causing genetic disorder has been reported, glycerol phenylbutyrate has been introduced as a treatment, and novel promising therapeutic avenues (including gene therapy) have been opened. Several factors including the impact of the first edition of these guidelines (frequently read and quoted) may have increased awareness among health professionals and patient families. However, under-recognition and delayed diagnosis of UCDs still appear widespread. It was therefore necessary to revise the original guidelines to ensure an up-to-date frame of reference for professionals and patients as well as for awareness campaigns. This was accomplished by keeping the original spirit of providing a trans-European consensus based on robust evidence (scored with GRADE methodology), involving professionals on UCDs from nine countries in preparing this consensus. We believe this revised guideline, which has been reviewed by several societies that are involved in the management of UCDs, will have a positive impact on the outcomes of patients by establishing common standards, and spreading and harmonizing good practices. It may also promote the identification of knowledge voids to be filled by future research.

Split-graft liver transplantation from an adult donor with an unrecognized UCD to a pediatric and adult recipient

We report the outcomes of an adult and pediatric split liver transplant from an adult male donor who died due to an unrecognized UCD, OTC deficiency. Recognizing inborn errors of metabolism can be challenging, especially in adult centers where such disorders are rarely encountered. Shortage of donors for liver transplantation has led to procedures to maximize donor utilization, such as split and live donor grafts. The cause of death should be ascertained before accepting a cadaveric donor organ.

Developmental and psychiatric presentations of inherited metabolic disorders

Pediatric neurologists and developmental pediatricians may evaluate patients with primary or associated behavioral and academic concerns. A critical element of the evaluation involves determining that the child's condition is not better explained by underlying inherited metabolic disorders. In this review, psychiatric and behavioral presentations of inherited metabolic disorders are discussed via several case studies. Key features of vignettes will illustrate when to consider these disorders in evaluating children referred for psychiatric and behavioral changes, after more common etiologies have been excluded. We seek to develop a better understanding of key clinical pearls to help identify children with an inherited metabolic disorder to account for behavioral or academic concerns.

Suggested guidelines for the diagnosis and management of urea cycle disorders

Urea cycle disorders (UCDs) are inborn errors of ammonia detoxification/arginine synthesis due to defects affecting the catalysts of the Krebs-Henseleit cycle (five core enzymes, one activating enzyme and one mitochondrial ornithine/citrulline antiporter) with an estimated incidence of 1:8.000. Patients present with hyperammonemia either shortly after birth (~50%) or, later at any age, leading to death or to severe neurological handicap in many survivors. Despite the existence of effective therapy with alternative pathway therapy and liver transplantation, outcomes remain poor. This may be related to underrecognition and delayed diagnosis due to the nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity. These guidelines aim at providing a trans-European consensus to: guide practitioners, set standards of care and help awareness campaigns. To achieve these goals, the guidelines were developed using a Delphi methodology, by having professionals on UCDs across seven European countries to gather all the existing evidence, score it according to the SIGN evidence level system and draw a series of statements supported by an associated level of evidence. The guidelines were revised by external specialist consultants, unrelated authorities in the field of UCDs and practicing pediatricians in training. Although the evidence degree did hardly ever exceed level C (evidence from non-analytical studies like case reports and series), it was sufficient to guide practice on both acute and chronic presentations, address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Also, it identified knowledge voids that must be filled by future research. We believe these guidelines will help to: harmonise practice, set common standards and spread good practices with a positive impact on the outcomes of UCD patients.

Personalized medicine: ethics for clinical trials

Modern ethical codes in medicine were developed following World War II to provide respect for persons, beneficence, and justice in clinical research. Clinical trial medicine involves greater scrutiny than most research activities. In every instance, clinical trials have institutional review boards to ensure the medical procedure under study complies with regulatory requirements, privacy, informed consent, good practices, safety monitoring, adverse events reporting, and is free of conflicting interests. Mandatory training in medical ethics for all clinical staff is becoming more common, and at some institutions, knowledgeable patient advocates play a watchdog role. In personalized medicine, each patient becomes a clinical trial of one, based on the uniqueness of the person's illness and the relatively tailored treatment. These features imply a shared responsibility between the patient and the researchers because uncertainty exists over the outcome for each individual patient. This chapter introduces ethical considerations using case studies, with historical context, and describes general ethical guidelines for initiating a clinical trial.

Brain imaging in urea cycle disorders

Urea cycle disorders (UCD) represent a group of rare inborn errors of metabolism that carry a high risk of mortality and neurological morbidity resulting from the effects of accumulation of ammonia and other biochemical intermediates. These disorders result from single gene defects involved in the detoxification pathway of ammonia to urea. UCD include deficiencies in any of the six enzymes and two membrane transporters involved in urea biosynthesis. It has previously been reported that approximately half of infants who present with hyperammonemic coma in the newborn period die of cerebral edema; and those who survive 3days or more of coma invariably have intellectual disability [1]. In children with partial defects there is an association between the number and severity of recurrent hyperammonemic (HA) episodes (i.e. with or without coma) and subsequent cognitive and neurologic deficits [2]. However, the effects of milder or subclinical HA episodes on the brain are largely unknown. This review discusses the results of neuroimaging studies performed as part of the NIH funded Rare Diseases Clinical Research Center in Urea Cycle Disorders and focuses on biomarkers of brain injury in ornithine transcarbamylase deficiency (OTCD). We used anatomic imaging, functional magnetic resonance imaging (fMRI), diffusion-tensor imaging (DTI), and (1)H/(13)C magnetic resonance spectroscopy (MRS) to study clinically stable adults with partial OTCD. This allowed us to determine alterations in brain biochemistry associated with changes in cell volume and osmolarity and permitted us to identify brain biomarkers of HA. We found that white matter tracts underlying specific pathways involved in working memory and executive function are altered in subjects with OTCD (as measured by DTI), including those heterozygous women who were previously considered asymptomatic. An understanding of the pathogenesis of brain injury in UCD is likely to advance our knowledge of more common disorders of liver dysfunction.

n of 1 trial for an ornithine transcarbamylase deficiency carrier

Ornithine transcarbamylase deficiency (OTCD) is an X-linked disorder of the urea cycle. It is often fatal in affected males. Treatment for affected individuals includes dietary protein restriction, activation of alternative pathways of nitrogen excretion and L-arginine supplementation. Depending on the amount of X chromosome inactivation skewing, females show variable clinical manifestations, and sometimes the need for treatment, including medications, is unclear. We conducted an n of 1 randomized controlled trial on an obligate OTC carrier. The treating physician and patient were blinded to treatment. Either placebo capsules or L-arginine capsules were given for weekly periods. Weekly efficacy indicators included plasma arginine and glutamine levels and a quality of life/mood assessment questionnaire scale. Clear evidence of benefit with L-arginine compared to placebo was shown. This is the first time an n of 1 randomized controlled trial has been reported for an X-linked metabolic condition. Despite some logistic hurdles, we have demonstrated that this method was an effective tool for determining the value of treatment. We propose that other rare metabolic conditions may be amenable to such trials, if the benefit of treatment is in doubt.

Hyperammonemia in the ICU

Patients experiencing acute elevations of ammonia present to the ICU with encephalopathy, which may progress quickly to cerebral herniation. Patient survival requires immediate treatment of intracerebral hypertension and the reduction of ammonia levels. When hyperammonemia is not thought to be the result of liver failure, treatment for an occult disorder of metabolism must begin prior to the confirmation of an etiology. This article reviews ammonia metabolism, the effects of ammonia on the brain, the causes of hyperammonemia, and the diagnosis of inborn errors of metabolism in adult patients.

Hyperammonemia encephalopathy: an important cause of neurological deterioration following chemotherapy

Idiopathic hyperammonemic encephalopathy is an uncommon but frequently fatal complication of chemotherapy. It is characterised by abrupt alteration in mental status with markedly elevated plasma ammonia levels in the absence of obvious liver disease or any other identifiable cause, and frequently results in intractable coma and death. It usually occurs in patients with haematologic malignancies during the period of neutropenia following cytoreductive therapy or bone marrow transplantation, and in solid organ malignancies treated with 5-fluorouracil. Although the aetiology of this syndrome is yet to be determined, it appears to be multi-factorial in nature. Optimal management remains to be formally established, and the critical step is increased awareness of the syndrome by measurement of plasma ammonium levels in patients with neurological symptoms, leading to early diagnosis and the prompt implementation of therapy.

Hyperammonemia, bane of the brain

Ammonia, normally produced from catabolism of amino acids, is a deadly neurotoxin. As such, the concentration of free ammonia in the blood is very tightly regulated and is exceeded by two orders of magnitude by its physiologic derivative, urea. The normal capacity for urea production far exceeds the rate of free ammonia production by protein catabolism under normal circumstances, such that any increase in free blood ammonia concentration is a reflection of either biochemical or pharmacologic impairment of urea cycle function or fairly extensive hepatic damage. Clinical signs of hyperammonemia occur at concentrations > 60 micromol/L and include anorexia, irritability, lethargy, vomiting, somnolence, disorientation, asterixis, cerebral edema, coma, and death; appearance of these findings is generally proportional to free ammonia concentration, is progressive, and is independent of the primary etiology. Causes of hyperammonemia include genetic defects in the urea cycle ("primary") or organic acidemias ("secondary"), as well as genetic or acquired disorders resulting in significant hepatic dysfunction. Thus, because of the neurotoxic implications of hyperammonemia and the typical absence of other specific laboratory abnormalities, appearance of the clinical signs should trigger an emergent search for elevated blood ammonia concentration.

Cognitive outcome in urea cycle disorders

Despite treatment, cognitive and motor deficits are common in individuals with inherited urea cycle disorders. However, the extent to which the deficits involve specific cognitive or sensorimotor domains is unknown. Furthermore, little is known about the neurochemical basis of cognitive impairment in these disorders. This paper reviews studies of cognitive and motor dysfunction in urea cycle disorders, and discusses potential venues for investigation of the underlying neural basis that may elucidate these defects. Such methods of investigation may serve as a model for studying the relationship between genes, biochemical markers, brain function, and behavior in other metabolic diseases.

Neurological outcome of patients with ornithine carbamoyltransferase deficiency

BACKGROUND

Ornithine carbamoyltransferase (OCT) deficiency is the commonest of the inherited urea cycle disorders.

AIMS

To determine the long term neurological and cognitive outcome of continuously treated surviving patients.

METHODS

Twenty eight surviving children (five boys) with OCT deficiency who had been treated continuously with a low protein diet and alternative pathway therapy were identified. Those aged 5-16 years had a detailed neurological examination and psychometric testing.

RESULTS

Four presented in the neonatal period and four were treated prospectively following antenatal diagnosis. Median (range) age at diagnosis for the later onset group was 19 (2-144) months; median time between onset of symptoms and diagnosis was 10 (2-48) months. Nine children had had less than three episodes of hyperammonaemic encephalopathy, the others more. Seven had focal abnormalities on neurological examination; 14 had global cognitive impairment; four had a normal IQ but specific learning difficulties. Sixteen underwent neuroimaging which was normal in three, showed focal abnormalities of the cerebral hemispheres in six, and global cerebral atrophy in seven.

CONCLUSION

Eighteen of 28 surviving children with OCT deficiency had disabling neurological complications. Plasma ammonia at diagnosis was the only factor that predicted this outcome. While most neurological complications could be attributed to hyperammonaemic encephalopathy, other mechanisms may also contribute to the neurological abnormalities.

Hyperammonemia in urea cycle disorders: role of the nephrologist

Hyperammonemia associated with inherited disorders of amino acid and organic acid metabolism is usually manifested by irritability, somnolence, vomiting, seizures, and coma. Although the majority of these patients present in the newborn period, they may also present in childhood, adolescence, and adulthood with failure to thrive, persistent vomiting, developmental delay, or behavioral changes. Persistent hyperammonemia, if not treated rapidly, may cause irreversible neuronal damage. After the diagnosis of hyperammonemia is established in an acutely ill patient, certain diagnostic tests should be performed to differentiate between urea cycle defects and other causes of hyperammonemic encephalopathy. In a patient with a presumed inherited metabolic disorder, the aim of therapy should be to normalize blood ammonia levels. Recent experience has provided treatment guidelines that include minimizing endogenous ammonia production and protein catabolism, restricting nitrogen intake, administering substrates of the urea cycle, administering compounds that facilitate the removal of ammonia through alternative pathways, and, in severe cases, dialysis therapy. Initiation of dialysis in the encephalopathic patient with hyperammonemia is indicated if the ammonia blood level is greater than three to four times the upper limit of normal. Hemodialysis is the most effective treatment for rapidly reducing blood ammonia levels. Continuous hemofiltration and peritoneal dialysis are also effective modalities for reducing blood ammonia levels. An improved understanding of the metabolism of ammonia and neurological consequences of hyperammonemia will assist the nephrologist in providing optimal care for this high-risk patient population.

Asymptomatic and late-onset ornithine transcarbamylase (OTC) deficiency in males of a five-generation family, caused by an A208T mutation

In a large five-generation Polish family, late-onset ornithine transcarbamylase (OTC) deficiency in males segregated with the missense mutation Ala208Thr (A208T), and all heterozygous females were asymptomatic. No other mutations were found in the coding sequences and intron-exon boundaries of the OTC gene. Surprisingly, the mutation originated from the great-grandfather of the index patient who died at age 59 of liver carcinoma. He never had dietary restrictions or hyperammonemic spells throughout life and appears to be the oldest male reported with OTC deficiency. The index patient had a severe OTC deficiency (3% of normal). Eight males died suddenly at ages 4 months to 23 years (average 14 years) after a foudroyant episode triggered by a common infection. The patients remained undiagnosed for 28 years because a metabolic defect was not considered to be the cause of the acute episodes. Recognition of the familial pattern of inheritance was initially unnoticed since the patients were admitted to eight different hospitals. DNA analysis predicted that two 'healthy' boys also had OTC deficiency, which was confirmed by abnormal results of allopurinol challenge tests. Initial suspicion of OTC deficiency in such families is complicated, since symptoms can develop at any age, or even remain absent. This obscures the typical pattern of X-linked inheritance in small families.

Vomiting, ataxia, and altered mental status in an adolescent: late-onset ornithine transcarbamylase deficiency

A case of a 13-year-old boy with protracted vomiting, ataxia, and altered mental status, ultimately diagnosed with late-onset ornithine transcarbamylase (OTC) deficiency, is presented. OTC deficiency is the most common urea cycle defect and typically is diagnosed in male infants with irritability, poor feeding, vomiting, lethargy, and often death caused by the effects of hyperammonemia. Late-onset OTC deficiency has been described in patients of all ages. The presenting symptoms in these patients vary but the most common are vomiting and lethargy. The pathophysiology, clinical features, differential diagnosis, and treatment of this disorder are discussed. Because of the risks of serious consequences, early detection and treatment of OTC deficiency and hyperammonemic episodes are mandatory. Emergency physicians caring for children and adults need to be aware of the spectrum of clinical presentations of OTC deficiency, including late-onset disease.

Recurrent episodes of bizarre behavior in a boy with ornithine transcarbamylase deficiency: diagnostic failure of protein loading and allopurinol challenge tests

Recurrent episodes of bizarre behavior were the only clinical symptoms that finally led to the diagnosis of ornithine transcarbamylase deficiency in an 8-year-old boy. The suspected diagnosis could not be confirmed with the use of current challenge tests. The response to a high-protein diet for 24 hours appeared to be a helpful diagnostic aid.

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.

Restoration of nitrogen homeostasis in a man with ornithine transcarbamylase deficiency

We evaluated the hypothesis that sodium phenylbutyrate-induced phenylacetylglutamine biosynthesis in a man with partial ornithine transcarbamylase (OTC) deficiency has a dual effect; it provides an additional vehicle for waste nitrogen excretion, and in the process it suppresses the patient's residual urea N synthesis, which then may be available for N homeostasis if the need arises. A 38-year-old man was studied over three periods. Period I was a control period during which he received a fixed caloric and N intake plus L-citrulline. Phenylbutyrate was added in period II and was maintained during period III, during which his N intake was increased. Plasma levels of ammonium and glutamine and net urea N synthesis were measured in each period; phenylacetylglutamine N synthesis was measured in periods II and III. These studies demonstrated that phenylbutyrate administration led to a 73% decrease in net de novo urea N synthesis during period II, which subsequently increased threefold in period III in response to the increased N intake. Phenylacetylglutamine N synthesis was 2.27 g/d, similar to his estimated maximum net urea N synthesis of 2.65 g/d. During periods II and III, his plasma levels of ammonium and glutamine improved as compared with period I when they were abnormally high. We conclude that sodium phenylbutyrate treatment of patients with urea cycle disorders who have significant residual enzyme activity results in both an improvement in waste N excretion and improved N homeostasis as a result of the generation of a reserve urea N synthetic capacity. This therapeutic approach may be useful in other nitrogen accumulation decreases, eg, portal-systemic encephalopathy.

Orthotopic liver transplantation in liver-based metabolic disorders

The efficacy of orthotopic liver transplantation (OLT) in the management of more common liver-based metabolic disorders associated with severe liver damage, alpha-1-antitrypsin deficiency (PIZZ), Wilson disease and tyrosinaemia has been demonstrated and indications defined. An early mortality in excess of 15% and finite resources limit its use. Phenotypic heterogeneity make the precise indication in other disorders less certain. In disorders in which endstage liver disease is less frequent such as cystic fibrosis, haemochromatosis and galacosaemia it has been a very effective therapy. It has been used with encouraging results in disorders in which the liver is structurally normal such as Crigler-Najjar type I, primary hyperoxaluria type I and primary hypercholesterolaemia. In these it should be performed before there is permanent damage to brain, kidneys or heart. OLT in the short term prevents hyperammonaemic coma in urea cycle defects and may prevent extrahepatic disease in glycogen storage disease type IV. Its limitation in reversing all metabolic effects in these and other disorders is discussed. It is ineffective in protoporphyria or Niemann Pick disease type II (Sea Blue Histiocyte syndrome) in which the transplanted liver acquires the lesions of the initial disorder and extrahepatic features progress. Early referral provides optimum circumstances to assess the benefits of OLT as compared with those of other forms of management and to achieve transplantation at the ideal time. The place of OLT in management will require constant review as metabolic disorders are better defined, new forms of therapy evolve and as techniques of liver transplantation and modes of immunosuppression improve.

Late-onset ornithine transcarbamylase deficiency in male patients

We report on 21 male patients who presented after 28 days of age with ornithine transcarbamylase (OTC) deficiency, which we define as late-onset OTC deficiency. These patients appeared normal at birth, but irritability, vomiting, and lethargy, which were often episodic, later developed. The age at presentation ranged from 2 months to 44 years. Biochemical testing revealed hyperammonemia, hyperglutaminemia, hypocitrullinemia, increased urinary orotate excretion, and decreased liver OTC activity measured in vitro, which ranged from 0% to 15% of normal. Male patients who were older at presentation had a somewhat different pattern of presenting symptoms and were more likely to die. These data illustrate the phenotypic variability of OTC deficiency. Unexplained episodes of repetitive or protracted vomiting in association with progressive alterations in behavior or neurologic findings should suggest the diagnosis of a urea cycle defect (or another symptomatic inborn error of metabolism), regardless of the age or medical history of the patient.

Sporadic late onset ornithine transcarbamylase deficiency in a boy with somatic mosaicism for an intragenic deletion

Somatic mosaicism for a deletion in the ornithine transcarbamylase gene is described in a boy with sporadic late onset ornithine transcarbamylase deficiency. These findings are discussed in relation to the clinical picture of the patient and in relation to genetic counseling.