Urea cycle disorders in adult patients

INTRODUCTION: Urea cycle disorders (UCD) usually present after 24 h to 48 h of life with failure to thrive, lethargy and coma leading to death, but milder forms may occur from infancy to adulthood. STATE OF THE ART: Survival of children with UCD has significantly improved and the need for transitional care to adulthood has emerged. Adult onset UCD present with chronic or acute neurological, psychiatric and digestive symptoms associated with protein avoidance. Ornithine transcarbamylase (OTC) deficiency, which is inherited as an X-linked disorder, is the most well-described UCD in adults. Acute decompensations associate the triad of encephalopathy, respiratory alkalosis and hyperammonemia. Acute encephalopathy is characterized by brain edema, which is life-threatening without treatment. Specific urea cycle enzyme deficiency can be suspected in the presence of abnormal plasma amino acids concentrations and urinary excretion of orotic acid. A measurement enzyme activity in appropriate tissue, or DNA analysis if available, is required for diagnosis. Treatment requires restriction of dietary protein intake and the use of alternative pathways of waste nitrogen excretion with sodium benzoate and sodium phenylbutyrate. Patients with acute forms may need hemodialysis or hemodiafiltration. Therapeutic goals for OTC deficiency are to maintain plasma ammonia<80 micromol/L, plasma glutamine<1,000 micromol/L, argininemia 80-150 micromol/L and branched chain amino acids within the normal range, in order to prevent episodes of potentially lethal acute hyperammonemia. CONCLUSION: Potentially fatal acute hyperammonemia may occur in male or female patients at any age. Ammonia should be measured promptly in case of acute neurological and psychiatric symptoms or coma.     

Rejection encephalopathy. An acute neurological syndrome complicating renal transplantation

Fifteen episodes of encephalopathy have been studied in 13 renal transplant recipients. All episodes of encephalopathy occurred during an acute rejection crisis. Clinical and biochemical features were recorded during rejection crises associated with encephalopathy and in an equal number of uncomplicated rejection episodes in the same patients. Encephalopathy was related to the severity of the rejection crisis and not to other features such as blood pressure, fever, steroid therapy or plasma electrolytes. The definition of the syndrome of rejection encephalopathy and its relation to the severity of the rejection has important therapeutic implications. Steroid therapy should not be withdrawn or reduced because of acute neurological features. Control of hypertension, fluid overload and electrolyte imbalance, in addition to treatment of the rejection episode, are necessary to reverse the encephalopathy. The prognosis of this syndrome is excellent with no long-term sequelae.     

Ammonia: Key factor in the pathogenesis of hepatic encephalopathy

There is substantial clinical and experimental evidence to suggest that ammonia toxicity is a major factor in the pathogenesis of hepatic encephalopathy associated with subacute and chronic liver disease. Ammonia levels in patients with severe liver disease are frequently found to be elevated both in blood and cerebrospinal fluid (csf). Hepatic encephalopathy results in neuropathological damage of a similar nature (Alzheimer type II astrocytosis) to that found in patients with congenital hyperammonemia resulting from inherited defects of urea cycle enzymes. Following portocaval anastomosis in the rat, blood ammonia concentration is increased 2-fold, and brain ammonia is found to be increased 2–3-fold. Administration of ammonia salts or resins to rats with a portocaval anastomosis results in coma and in Alzheimer type II astrocytosis. Since the CNS is devoid of effective urea cycle activity, ammonia removal by brain relies on glutamine formation. Cerebrospinal fluid and brain glutamine are found to be significantly elevated in cirrhotic patients with encephalopathy and in rats following portocaval anastomosis. In both cases, glutamine is found to be elevated in a region-dependent manner. Several mechanisms have been proposed to explain the neurotoxic action of ammonia. Such mechanisms include: (i) Modification of blood-brain barrier transport; (ii) alterations of cerebral energy metabolism; (iii) direct actions on the neuronal membrane; and (iv) decreased synthesis of releasable glutamate, resulting in impaired glutamatergic neurotransmission.     

Role of carnitine and fatty acid oxidation and its defects in infantile epilepsy

Defects in fatty acid oxidation are a source of major morbidity and are potentially rapidly fatal. Fatty acid oxidation defects encompass a spectrum of clinical disorders, including recurrent hypoglycemic, hypoketotic encephalopathy or Reye-like syndrome in infancy with secondary seizures and potential developmental delay, progressive lipid storage myopathy, recurrent myoglobinuria, neuropathy, and progressive cardiomyopathy. As all of the known conditions are inherited as autosomal recessive diseases, there is often a family history of sudden infant death syndrome in siblings. Early recognition and prompt initiation of therapy and the institution of preventive measures may be life saving and significantly decrease long-term morbidity, particularly with respect to central nervous system sequelae. Seizures may be the result of cerebral bioenergetic failure associated with acute episodes of hypoglycemic, hypoketotic encephalopathy, or hypoxic-ischemic encephalopathy in the context of cardiac arrhythmias and/or cardiomyopathy. This review provides an overview of the fatty acid oxidation pathway and the central role of carnitine, as well as a discussion of normal fasting adaptation and the critical metabolic adaptations that occur at birth. The increased vulnerability of infants and young children to fasting and defective fatty acid oxidation is discussed in the context of the heightened bioenergetic demands of the developing brain. Clinical and laboratory features of specific genetic defects in fatty acid oxidation, approaches to diagnosis, and current treatment methodologies are described. Indications for carnitine supplementation in childhood epilepsy are also discussed.     

Pyruvate dehydrogenase deficiency presenting as intermittent isolated acute ataxia

OBJECTIVE: The aim of this study is to report and emphasize unusual presentations of pyruvate dehydrogenase (PDH) deficiency (OMIM 312170). METHODS: PDH activity and PDHA1 gene were studied in two siblings presenting with intermittent ataxia in childhood. Similar presentations in reported PDH-deficient patients were searched for using the Medline database. RESULTS: Both patients had PDH deficiency caused by a new mutation (G585C) in the PDHA1 gene, which is predicted to replace a highly conserved glycine at codon 195 by alanine. Although this mutation lies within the thiamine pyrophosphate binding domain, there was no thiamine responsiveness IN VIVO. The patients presented recurrent episodes of acute isolated ataxia in infancy. Both had normal blood and CSF lactate levels. Although symptoms initially resolved between episodes during the first decade, both patients subsequently worsened and developed progressive and severe encephalopathy, leading to death in their twenties. The spectrum of intermittent presentations in PDH deficiency includes episodic ataxia, intermittent peripheral weakness, recurrent dystonia and extrapyramidal movement disorders. CONCLUSIONS: PDH deficiency should be considered in patients with unexplained intermittent and recurrent acute neurological symptoms. Long-term prognosis and outcome remain uncertain. PDH deficiency can occur even with normal CSF lactate concentration.     

Soluble brain proteins in dialysis encephalopathy

Summary Soluble brain proteins were analyzed regionally in a case of dialysis encephalopathy and compared to the findings in patients dying from uncomplicated uremia and acute myocardial infarction. Sixteen individual proteins were quantitated and the results may indicate that dialysis encephalopathy is accompanied by defects in the blood-brain barrier. However, such a postulate does not explain why certain proteins (-trace protein) occur at very low concentrations in dialysis encephalopathy.     

Thiamine deficiency in childhood with attention to genetic causes: Survival and outcome predictors

Primary and secondary conditions leading to thiamine deficiency have overlapping features in children, presenting with acute episodes of encephalopathy, bilateral symmetric brain lesions, and high excretion of organic acids that are specific of thiamine‐dependent mitochondrial enzymes, mainly lactate, alpha‐ketoglutarate, and branched chain keto‐acids. Undiagnosed and untreated thiamine deficiencies are often fatal or lead to severe sequelae. Herein, we describe the clinical and genetic characterization of 79 patients with inherited thiamine defects causing encephalopathy in childhood, identifying outcome predictors in patients with pathogenic SLC19A3 variants, the most common genetic etiology. We propose diagnostic criteria that will aid clinicians to establish a faster and accurate diagnosis so that early vitamin supplementation is considered. Ann Neurol 2017;82:317–330     

Clinical and MRI characteristics of acute encephalopathy in congenital adrenal hyperplasia

Acute encephalopathy in childhood is frequently associated with common infections, especially in East Asia. Various types have been identified although many cases remain unclassified. Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease presenting impairment of cortisol biosynthesis. We report three CAH children with acute infection-related encephalopathy. They exhibited disturbed consciousness or seizures, which did not improve after glucocorticoid administration, accompanied by clinical and laboratory findings of adrenal insufficiency. Brain MRI disclosed various patterns of white matter lesions, suggesting different types of acute encephalopathy such as clinically mild encephalitis/encephalopathy with a reversible splenial lesion or hemiconvulsion-hemiplegia syndrome. Acute encephalopathy should be considered and brain MRI immediately performed when impairment of consciousness does not improve after intravenous glucocorticoid administration in CAH patients. Further research is required to elucidate the epidemiology and pathogenic mechanisms of acute encephalopathy in CAH.     

Convulsive Status Epilepticus in Children

Summary: Status epilepticus (SE) occurs most commonly in infancy and childhood. Children with prior neurological abnormalities are most susceptible. More than 90% of cases are convulsive and the majority are generalized. SE may occur in the setting of an acute illness, in patients with established epilepsy or as a first unprovoked seizure. The etiology can be classified as idiopathic, remote symptomatic, febrile, acute symptomatic, or associated with a progressive encephalopathy. The morbidity and mortality of status have dramatically declined in recent years. Overall mortality in recent pediatric series was 3–10%, with almost all fatalities associated with acute central nervous system insults or progressive neurologic disorders. Neurological sequelae in children with idiopathic or febrile status are rare. Neurologically normal children with SE as their first unprovoked seizure have the same risk of experiencing subsequent seizures of any type as children who present with a brief first seizure. The risk of recurrent episodes of convulsive SE approaches 50% in neurologically abnormal children but is very low in neurologically normal children. The favorable outcome of SE in children may be related to advances in therapy and to the resistance of the immature brain to damage from seizures.     

Alterations in expression of genes coding for key astrocytic proteins in acute liver failure.

Cerebral edema and hepatic encephalopathy are major complications of acute liver failure. Brain herniation caused by increased intracranial pressure as a result of cell swelling is the major cause of death in this condition. Evidence available currently suggests that the rapid accumulation of ammonia by the brain is the major cause of the central nervous system complications of acute liver failure. Increased brain ammonia may cause cell swelling via the osmotic effects of an increase in astrocytic glutamine concentrations or by inhibition of glutamate removal from brain extracellular space. Acute liver failure results in altered expression of several genes in brain, some of which code for important proteins involved in CNS function such as the glucose (GLUT-1) and glutamate (GLT-1) transporters, the astrocytic structural protein glial fibrillary acidic protein (GFAP) the "peripheral-type" benzodiazepine receptor (PTBR) and the water channel protein, aquaporin IV. Loss of expression of GLT-1 results in increased extracellular brain glutamate in acute liver failure. Experimental acute liver failure also results in post-translational modifications of the serotonin and noradrenaline transporters resulting in increased extracellular concentrations of these monoamines. Therapeutic measures currently used to prevent and treat brain edema and encephalopathy in patients with acute liver failure include mild hypothermia and the ammonia-lowering agent L-ornithine-L-aspartate.     

Phenotypic Spectrum of Glucose Transporter Type 1 Deficiency Syndrome (Glut1 DS)

Glut1 deficiency syndrome (Glut1 DS) was originally described in 1991 as a developmental encephalopathy characterized by infantile onset refractory epilepsy, cognitive impairment, and mixed motor abnormalities including spasticity, ataxia, and dystonia. The clinical condition is caused by impaired glucose transport across the blood brain barrier. The past 5 years have seen a dramatic expansion in the range of clinical syndromes that are recognized to occur with Glut1 DS. In particular, there has been greater recognition of milder phenotypes. Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood. A number of patients present predominantly with movement disorders, sometimes without any accompanying seizures. In particular, paroxysmal exertional dyskinesia is now a well-documented clinical feature that occurs in individuals with Glut1 DS. A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise. Intellectual impairment may range from severe to very mild. Awareness of the broad range of potential clinical phenotypes associated with Glut1 DS will facilitate earlier diagnosis of this treatable neurologic condition. The ketogenic diet is the mainstay of treatment and nourishes the starving symptomatic brain during development.     

Headache and neuropsychic disorders in the puerperium: a case report with suspected deficiency of urea cycle enzymes

An enzymatic abnormality of the urea cycle is a metabolic disorder occasionally seen in adults, but particularly in the puerperium. The main risk is acute hyperammoniemic encephalopathy, leading to psychosis, coma and even death if not diagnosed promptly and treated appropriately. Headache is frequent in the puerperium normally manifesting between 3 and 6 days after delivery. We describe here a 39-year-old woman, who 3 days after delivery presented diffuse tension-type headache and depression, followed by behavioral disorders, psychomotor agitation, epileptic seizures, and finally coma 2 days later. Pregnancy and normal delivery: routine blood chemistry findings, CT scan, MR imaging, angio-MR of the brain, and lumbar puncture were normal. EEG when seizures started, it showed diffuse slowing, as in the case of metabolic encephalopathy. This led us to assay blood ammonia, which was high at >400 mmol. Liver function and abdominal US were normal; hence, we suspected a urea cycle enzymatic abnormality, and requested for genetic tests. These confirmed a congenital primary metabolic deficiency of arginine succinate synthetase, with high citrullinemia (type II, adult form). Dialysis was started promptly, with initially iv arginine, then orally, plus medical therapy for the hyperammoniemia and a low protein diet; plasma ammonia dropped swiftly to normal, and her state of consciousness gradually improved until all the clinical symptoms had resolved. Ammonia assay should always be considered in the first few days of the puerperium in women with headache and behavioral disorders, to exclude an inborn deficiency of the urea cycle, which may have gone unnoticed until then.

     

Late onset heterozygous ornithine transcarbamylase deficiency mimicking complex partial status epilepticus

A 57 year old woman with post-traumatic complex partial seizures was admitted because of recurrent episodes of altered mental state over the preceding 4 years, each lasting up to 5 days. There was a history of dietary protein intolerance since childhood and two of her daughters had died in the neonatal period from unexplained encephalopathies. In hospital she developed fluctuating confusion, amnesia, and sudden episodes of unresponsiveness. An EEG was consistent with complex partial status epilepticus but there was no response to benzodiazepines. Nasogastric feeding and sodium valproate were given and shortly afterwards she lapsed into a deep coma. Blood ammonia and urinary orotate were raised, and genetic testing confirmed that she was a carrier of a mutation in exon 3 of the ornithine transcarbamylase gene (C to T at position 92). Treatment with protein restriction, carnitine, and sodium phenylbutyrate led to a full recovery over a period of 3 months. To our knowledge this is the oldest age of onset yet described in a manifesting carrier. She is the fifth patient with heterozygous ornithine transcarbamylase deficiency reported to have had a severe reaction to sodium valproate. Hyperammonaemic encephalopathy should be considered in patients of any age who experience fluctuating confusion.     

Clinical features of encephalopathy in children with cancer requiring cranial magnetic resonance imaging

We analyzed acute neurotoxic problems attributable to chemotherapy or immunosuppression in the context of childhood neoplastic diseases, based on clinical and neuroradiologic findings. This retrospective single-center study reviewed the acute neurologic complications of 62 children receiving conventional chemotherapy or hematopoietic stem cell transplantation from July 2005-July 2008. We excluded patients with central nervous system metastasis and various neurotoxic manifestations not usually requiring cranial magnetic resonance imaging. Of 62 patients, 12 (19.3%) developed acute neurologic complications. The most common complications included posterior reversible encephalopathy syndrome in six of 12 (50%) patients, and Wernicke's encephalopathy in three of 12 (25%) patients. Other complications included chemical arachnoiditis, grey matter injury induced by postchemotherapeutic angiopathy, and leukoencephalopathy. Posterior reversible encephalopathy syndrome was accompanied by hypertensive episodes in most patients (5/6), and Wernicke's encephalopathy was evident with altered mental status in malnourished children. These data indicate that posterior reversible encephalopathy syndrome and Wernicke's encephalopathy are the predominant complications in children undergoing chemotherapy or hematopoietic stem cell transplantation. Early radiologic and clinical evaluation and prompt treatment for these complications are necessary to prevent their progression to irreversible brain damage.     

Different clinical manifestations of hyperammonemic encephalopathy

Valproate is an effective anticonvulsant. Although it is usually well tolerated, it has been associated with many neurological, hematopoietic, hepatic, and digestive system side effects. Among these side effects, hyperammonemia without clinical or laboratory evidence of hepatotoxicity is rare and is an important clinical consideration. The aim of this article was to evaluate the reasons for the unexpected symptoms observed in seven patients with epilepsy patients during valproate treatment. We evaluated seven adult patients with localization-related epilepsy who presented with different acute or subacute neurological symptoms related to valproate-induced hyperammonemic encephalopathy. Four of the seven patients had acute onset of confusion, decline in cognitive abilities, and ataxia. Two had subacute clinical symptoms, and the other patient had symptoms similar to those of acute toxicity. These unusual clinical symptoms and similar cases had not been reported in the literature before. Serum ammonia levels were elevated in all seven patients. After discontinuation of valproate, complete clinical improvement was observed within 5-10 days. On the basis of our work, we suggest that the ammonia levels of a patient who has new neurological symptoms and has been taking valproate must be checked. Clinicians should be aware that these clinical symptoms may be related to valproate-induced hyperammonemic encephalopathy. The symptoms have been observed to resolve dramatically after withdrawal of the drug.     

Detoxification of Ammonia in Mouse Cortical GABAergic Cell Cultures Increases Neuronal Oxidative Metabolism and Reveals an Emerging Role for Release of Glucose-Derived Alanine

Cerebral hyperammonemia is believed to play a pivotal role in the development of hepatic encephalopathy (HE), a debilitating condition arising due to acute or chronic liver disease. In the brain, ammonia is thought to be detoxified via the activity of glutamine synthetase, an astrocytic enzyme. Moreover, it has been suggested that cerebral tricarboxylic acid (TCA) cycle metabolism is inhibited and glycolysis enhanced during hyperammonemia. The aim of this study was to characterize the ammonia-detoxifying mechanisms as well as the effects of ammonia on energy-generating metabolic pathways in a mouse neuronal–astrocytic co-culture model of the GABAergic system. We found that 5 mM ammonium chloride affected energy metabolism by increasing the neuronal TCA cycle activity and switching the astrocytic TCA cycle toward synthesis of substrate for glutamine synthesis. Furthermore, ammonia exposure enhanced the synthesis and release of alanine. Collectively, our results demonstrate that (1) formation of glutamine is seminal for detoxification of ammonia; (2) neuronal oxidative metabolism is increased in the presence of ammonia; and (3) synthesis and release of alanine is likely to be important for ammonia detoxification as a supplement to formation of glutamine.     

Acute hemiparesis as the presenting sign in a heterozygote for ornithine transcarbamylase deficiency

Strokes in children occur in conjunction with cardiac disease, hematological disorders, trauma, intracranial infections and migraine. Recently several inborn errors of metabolism have been recognized as possible causes of stroke-like symptoms. We describe a female heterozygote of ornithine transcarbamylase deficiency, who presented with convulsions and right sided hemiplegia. MR-imaging of the brain demonstrated an acute ischemic lesion in the left hemisphere. In addition to other known metabolic causes of stroke like attacks urea cycle defects should be considered in the differential diagnosis of acute hemiplegia in childhood.     

Mitochondrial respiratory chain defects: underlying etiology in various epileptic conditions

PURPOSE: To determine if defects in mitochondrial respiratory chain enzyme complexes (MRCs) contribute to the etiology of childhood epilepsy. METHODS: We reviewed the clinical and laboratory features of 48 epileptic patients (23 male, 25 female) with MRC defects that were confirmed by biochemical assays using muscle biopsies. RESULTS: (1) Thirty-five cases (72.9%) were MRC I deficient, one case (2.1%) was MRC II deficient, 11 cases (22.9%) were MRC IV deficient, and one case (2.1%) had combined MRC I and IV deficiencies. (2) In our clinical diagnosis, there were 10 cases (20.8%) with Leigh disease and one case each with myopathy, encephalopathy, lactic acidosis, stroke-like episodes (MELAS) or Alpers' disease (2.1%). Most of the remaining cases (75.0%) had uncategorized mitochondrial cytopathy with nonspecific encephalopathy. (3) For epileptic classification, there were two cases (4.2%) of Ohtahara syndrome, 10 cases (20.8%) of West syndrome, 12 cases (25.0%) of Lennox-Gastaut syndrome, two cases (4.2%) of Landau-Kleffner syndrome, 14 cases (29.2%) of generalized epilepsy, and eight cases (16.7%) of partial epilepsy. (4) The mean age of seizure onset was 2.68 +/- 2.21 (range: 1 month - 5.5 years). (5) Magnetic resonance imaging (MRI) showed diffuse cortical atrophy in 34 cases (70.8%), basal ganglia signal changes in 18 cases (37.5%) and thalamus signal changes in 12 cases (25.0%). (6) A ketogenic diet produced clinical improvements, including seizure reduction and global functional improvement in 75% of 24 patients. CONCLUSIONS: MRC defects are one of the important causes of probably symptomatic childhood epilepsy. A ketogenic diet should be carefully considered for treatment of intractable epilepsy related to MRC defects.     

Distinguishing ischemic stroke from the stroke-like lesions of MELAS using apparent diffusion coefficient mapping

We report two patients with migraine, acute visual field defects and other neurological symptoms who were found to have high T(2) signal and FLAIR abnormalities on brain MRI in temporal and parieto-occipital regions. In these patients, the apparent diffusion coefficient (ADC) of their lesions was increased, distinguishing these lesions from those of ischemic stroke. Both were ultimately diagnosed with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). We conclude that conventional MRI when used with diffusion-weighted MR imaging may be invaluable in detecting mitochondrial-related CNS dysfunction.