Urea cycle defect: a case with MR and CT findings resembling infarct

Multimodal imaging in urea cycle-related neurological disease - What can imaging after hyperammonemia teach us?

BACKGROUND

Urea cycle-related brain disease may take on variable neuroimaging manifestations, ranging from normal to abnormal with or without a signature appearance. In the past, we have described the usefulness of multimodal imaging in identifying biomarkers of neuronal injury in UCD patients. In this study, we report unique findings in an adolescent male with neonatal-onset OTC deficiency after an episode of hyperammonemia.

MATERIALS AND METHODS

Multiplanar, multisequence MR imaging (T1WI, T2WI, T2 FLAIR, diffusion weighted images and gradient echo) of the brain was performed on seven separate occasions over the course following the acute illness; first five exams were performed within 28 days of admission and the final two exams were performed approximately 3 and 5 months later.

RESULTS

1.The initial MR revealed increased signal on T2WI in the basal ganglia, claustrum and frontoparietal white matter; which remained stable over time. By the 5th exam, signal changes had developed in frontal cortex; reflecting permanent injury. 2. DTI tractography of the corticospinal tracts displayed revealed diminution of the number of projectional and commissural fibers over time. 3. Blood flow measurements demonstrated hypoperfusion on the fifth exams followed by hyperperfusion on the final two studies. 4. MR spectroscopy demonstrated that glutamine was elevated during hyperammonemia with myoinositol reduction, reflecting osmotic buffering.

CONCLUSION

This particular multimodal magnetic resonance neuroimaging showed novel, temporally specific manifestations over the disease course in OTC deficiency. This prospective imaging study expands our understanding of the effect of hyperammonemia on the structure and biochemistry of the nervous system.

Urea cycle disorder presenting as bilateral mesial temporal sclerosis - an unusual cause of seizures: a case report and review of the literature

BACKGROUND

Urea cycle disorders are secondary to defects in the system converting ammonia into urea, causing accumulation of ammonia and other byproducts which are neurotoxic. Ornithine transcarbamylase deficiency is the most common of the urea cycle disorders and frequently presents with coma or seizures during hyperammonemia. However, seizures can also occur without metabolic decompensation.

CASE PRESENTATION

We describe a 23-year-old Chinese woman with urea cycle disorder who presented with confusion due to focal seizures arising from the left frontotemporal region. Interestingly, her ammonia levels remained normal during the seizures. Neuroimaging showed bilateral mesial temporal sclerosis. Her seizures were successfully controlled with two anti-epileptic medications.

CONCLUSIONS

This case adds evidence of the predisposition of the temporal lobe to injury in urea cycle disorder. Urea cycle disorder can lead to mesial temporal sclerosis which leads to increased susceptibility of patients to seizures regardless of their metabolic state.

Ornithine transcarbamylase deficiency presenting with acute reversible cortical blindness

Acute focal neurologic deficits are a rare but known presentation of ornithine transcarbamylase deficiency, particularly in females. We describe here a 6-year-old girl with newly diagnosed ornithine transcarbamylase deficiency who presents with an episode of acute cortical blindness lasting for 72 hours in the absence of hyperammonemia. Her symptoms were associated with a subcortical low-intensity lesion with overlying cortical hyperintensity on fluid-attenuated inversion recovery magnetic resonance imaging (MRI) of the occipital lobes. Acute reversible vision loss with these MRI findings is an unusual finding in patients with ornithine transcarbamylase deficiency. Our findings suggest a role for oxidative stress and aberrant glutamine metabolism in the acute clinical features of ornithine transcarbamylase deficiency even in the absence of hyperammonemia.

Antepartum ornithine transcarbamylase deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common type urea cycle enzyme deficiencies. This syndrome results from a deficiency of the mitochondrial enzyme ornithine transcarbamylase, which catalyzes the conversion of ornithine and carbamoyl phosphate to citrullin. Our case was a 28-year-old female diagnosed with OTCD following neurocognitive deficit during her first pregnancy. Although hyperammonemia was suspected as the cause of the patient's mental changes, there was no evidence of chronic liver disease. Plasma amino acid and urine organic acid analysis revealed OTCD. After combined modality treatment with arginine, sodium benzoate and hemodialysis, the patient's plasma ammonia level stabilized and her mental status returned to normal. At last she recovered without any damage left.

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.

Defects in amino acid catabolism and the urea cycle

Symptoms in patients with defects in amino acid catabolism and the urea cycle usually develop because of intoxication of accumulating metabolites. The cumulative prevalence of these disorders is considerable (at least>1:2000 newborns). Timely and correct intervention during the initial presentation and during later episodes is most important. Evaluation of metabolic parameters should be performed on an emergency basis in every patient with symptoms of unexplained metabolic crisis, intoxication, and/or unexplained encephalopathy. A substantial number of patients develop acute encephalopathy or chronic and fluctuating progressive neurological disease. The so-called cerebral organic acid disorders present with (progressive) neurological symptoms: ataxia, myoclonus, extrapyramidal symptoms, and "metabolic stroke." Important diagnostic clues, such as white matter abnormalities, cortical or cerebellar atrophy, and injury of the basal ganglia can be derived from cranial magnetic resonance imaging (MRI). Long-term neurological disease is common, particularly in untreated patients, and the manifestations are varied, the most frequent being (1) mental defect, (2) epilepsy, and (3) movement disorders. Successful treatment strategies are becoming increasingly available. They mostly require an experienced interdisciplinary team including a neuropediatrician and/or later on a neurologist.

High prevalence of neonatal presentation in Korean patients with citrullinemia type 1, and their shared mutations

Type 1 citrullinemia (CTLN1) often presents as a hyperammonemic encephalopathy in the neonatal period, but it can also develop in the late-infantile period and in adults. In addition, some patients can be identified in the presymptomatic period by neonatal or family member screening. In this study, twenty Korean patients with CTLN1 (19 families) were examined; fourteen patients with neonatal-onset, three with late-onset, and three that were identified presymptomatically. The 13 patients with hyperammonemic encephalopathy received continuous venovenous hemofiltration (CVVH) or peritoneal dialysis (PD). Although the hyperammonemia was relieved more effectively in the six patients on CVVH than the seven on PD, most of these patients suffered from severe neurologic deficits. Recurrent hyperammonemic episodes (7 pts, 35%), recurrent and reversible acute hepatic dysfunction (5 pts, 25%), and focal cerebral infarction (2 pts, 10%) were noted. The neonates with hyperammonemic encephalopathy had extensive brain injuries at the onset of hyperammonemia, followed by encephalomalacia and brain atrophy at quite an early age. Genetic testing for the ASS1 gene revealed a different mutation spectrum from those of other ethnicities; Three common mutations, c.421-2A>G (37.8%), c.1128-6_1188dup67 (18.9%), and p.Gly324Ser (16.2%), accounted for 73% of the mutations. The poor outcome was expected in patients with the peak ammonia level at onset over 600μmol/L, whose proportion was higher in the neonatal presentation group than in the presymptomatic/late presentation group. Our findings add to the current understanding of the ethnic diversity of CTLN1 from both clinical and genetic perspectives.

Urea cycle disorders: brain MRI and neurological outcome

BACKGROUND

Urea cycle disorders encompass several enzyme deficiencies that can result in cerebral damage, with a wide clinical spectrum from asymptomatic to severe.

OBJECTIVE

The goal of this study was to correlate brain MRI abnormalities in urea cycle disorders with clinical neurological sequelae to evaluate whether MRI abnormalities can assist in guiding difficult treatment decisions.

MATERIALS AND METHODS

We performed a retrospective chart review of patients with urea cycle disorders and symptomatic hyperammonemia. Brain MRI images were reviewed for abnormalities that correlated with severity of clinical neurological sequelae.

RESULTS

Our case series comprises six urea cycle disorder patients, five with ornithine transcarbamylase deficiency and one with citrullinemia type 1. The observed trend in distribution of brain MRI abnormalities as the severity of neurological sequelae increased was the peri-insular region first, extending into the frontal, parietal, temporal and, finally, the occipital lobes. There was thalamic restricted diffusion in three children with prolonged hyperammonemia. Prior to death, this site is typically reported to be spared in urea cycle disorders.

CONCLUSION

The pattern and extent of brain MRI abnormalities correlate with clinical neurological outcome in our case series. This suggests that brain MRI abnormalities may assist in determining prognosis and helping clinicians with subsequent treatment decisions.

Diffusion tensor imaging detects areas of abnormal white matter microstructure in patients with partial ornithine transcarbamylase deficiency

BACKGROUND AND PURPOSE

OTCD, an X-linked disorder, is the most common of the UCDs. Neonatal onset is associated with uniformly poor outcome. Males with late-onset OTCD show deficits in executive function, motor planning, and working memory. A broad phenotype is observed in heterozygous females. A specific neurobehavioral phenotype with white matter dysfunction and impaired attention and working memory has been described. The extent to which the deficits involve specific pathways in the brain is unknown. We hypothesized that DTI would disclose white matter microstructure in OTCD correlating with cognitive deficits.

MATERIALS AND METHODS

Nineteen adults with partial OTCD and 18 adult control subjects ages 19-59 years participated. MR imaging was performed by using a 3T whole-body scanner. Anisotropy was calculated from the eigenvalues of the diffusion tensor by using the FA metric and was compared between the study and control groups.

RESULTS

FA of the frontal white matter was significantly decreased in subjects, indicating changes in white matter microstructure. There was an inverse relationship between FA and disease severity, but not with age.

CONCLUSIONS

Findings of MR imaging in OTCD are often normal in patients with late-onset disease, heterozygotes, or in those not in hyperammonemic crisis. DTI was more sensitive than FSE T2-weighted imaging for detecting abnormalities in normal-appearing white matter. The extent of abnormality correlated with cognitive deficits. The location of the deficits in the frontal white matter is important because this area connects fibers that are vital to executive function, attention, and working memory.

Parieto-occipital encephalomalacia in neonatal hyperammonemia with ornithine transcarbamylase deficiency: A case report

Urea cycle disorders are congenital metabolic disorders that often cause episodic hyperammonemia. Neuroimaging in episodic hyperammonemia demonstrates several patterns of brain injuries, including focal lesions in the lentiform nucleus, insula, cingulate gyrus, and perirolandic fissure, as well as diffuse cerebral edema. In cases with neonatal onset of hyperammonemia, similar lesions have also been reported. We herein report a boy with severe neonatal hyperammonemia caused by ornithine transcarbamylase deficiency. He presented with parieto-occipital encephalomalacia, which resembles severe neonatal hypoglycemia on magnetic resonance imaging. This radiological finding may indicate parieto-occipital vulnerability not only to hypoglycemia but also to hyperammonemia.

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.

Neurologic damage and neurocognitive dysfunction in urea cycle disorders

Although the survival of patients who have urea cycle disorders has improved with the use of modalities such as alternative pathway therapy and hemodialysis, neurologic outcome is suboptimal. Patients often manifest with a variety of neurologic abnormalities, including cerebral edema, seizures, cognitive impairment, and psychiatric illness. Current hypotheses of the pathogenesis underlying brain dysfunction in these patients have focused on several lines of investigation, including the role of glutamine in causing cerebral edema, mitochondrial dysfunction leading to energy failure and the production of free radicals, and altered neurotransmitter metabolism. Advances in understanding the pathogenetic mechanisms underlying brain impairment in urea cycle disorders may lead to the development of therapies designed to interfere with the molecular cascade that ultimately leads to cerebral edema and other brain pathological findings.

1H MRS identifies symptomatic and asymptomatic subjects with partial ornithine transcarbamylase deficiency

OBJECTIVE

To evaluate brain metabolism in subjects with partial ornithine transcarbamylase deficiency (OTCD) utilizing (1)H MRS.

METHODS

Single-voxel (1)H MRS was performed on 25 medically-stable adults with partial OTCD, and 22 similarly aged controls. Metabolite concentrations from frontal and parietal white matter (FWM, PWM), frontal gray matter (FGM), posterior cingulate gray matter (PCGM), and thalamus (tha) were compared with controls and IQ, plasma ammonia, glutamine, and disease severity.

RESULTS

Cases ranged from 19 to 59 years; average 34 years; controls ranged from 18 to 59 years; average 33 years. IQ scores were lower in cases (full scale 111 vs. 126; performance IQ 106 vs. 117). Decreased myoinositol (mI) in FWM (p=0.005), PWM (p<0.001), PCGM (p=0.003), and tha (p=0.004), identified subjects with OTCD, including asymptomatic heterozygotes. Glutamine (gln) was increased in FWM (p<0.001), PWM (p<0.001), FGM (p=0.002), and PCGM (p=0.001). Disease severity was inversely correlated with [mI] in PWM (r=-0.403; p=0.046) and directly correlated with [gln] in PCGM (r=0.548; p=0.005). N-Acetylaspartate (NAA) was elevated in PWM (p=0.002); choline was decreased in FWM (p=0.001) and tha (p=0.002). There was an inverse relationship between [mI] and [gln] in cases only. Total buffering capacity (measured by [mI/mI+gln] ratio, a measure of total osmolar capacity) was inversely correlated with disease severity in FWM (r=-0.479; p=0.018), PWM (r=-0.458; p=0.021), PCGM (r=-0.567; p=0.003), and tha (r=-0.345; p=0.037).

CONCLUSION

Brain metabolism is impaired in partial OTCD. Depletion of mI and total buffering capacity are inversely correlated with disease severity, and serve as biomarkers.

1H MRS allows brain phenotype differentiation in sisters with late onset ornithine transcarbamylase deficiency (OTCD) and discordant clinical presentations

We used (1)H MRS to evaluate brain metabolic differences in sisters with partial ornithine transcarbamylase deficiency (OTCD) who had discordant clinical symptoms and urea synthetic capabilities to assess whether a brain biomarker of partial OTCD correlated with urea synthetic ability and clinical severity. We performed single voxel 3.0T (1)H MRS in two adult sisters with partial OTCD, one symptomatic and one asymptomatic, in a stable medical state and compared it to one age matched adult control, as well as data collected on an additional 13 subjects with partial OTCD and 12 controls. Data from voxels placed in frontal and parietal white matter (FWM, PWM), posterior cingulate gray matter (PCGM), and thalamus (tha), were corrected for partial volume and analyzed using "LCModel". All three subjects as well as the symptomatic mother of the two sisters, had neurocognitive testing, plasma ammonia levels, plasma amino acid, and urine organic acid analysis. Previous urea synthetic capabilities had been measured by stable isotope analysis. We found IQ scores to be inversely related to symptoms. Decreased myoinositol (mI) identified OTCD subjects, even the sister who is asymptomatic, in the posterior parietal white matter and frontal white matter. Brain metabolism is impaired in partial OTCD. Abnormal metabolism in apparently asymptomatic OTCD females may provide an explanation for neurocognitive impairments previously reported. The concentration of mI seen on (1)H MRS in PWM and FWM in this family could be used to deduce clinical symptomatology and may serve as a non-invasive marker of brain liability in OTCD.

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.

Two cases of citrullinaemia presenting with stroke

Urea cycle disorders are known to be unusual causes of stroke. We report two infant cases of citrullinaemia that both initially presented with a stroke and suggest that urea cycle disorders should be included in the differential diagnosis of unexplained stroke during infancy and childhood.

Urea Cycle Disorders: Clinical Presentation Outside the Newborn Period

Although most commonly associated with infancy, the majority of individuals with urea cycle disorders (UCDs) present outside the neonatal period, frequently in childhood. Signs and symptoms are often vague, but recurrent; fulminant presentations associated with acute illness are also common. A disorder of urea cycle metabolism should be considered in children who have recurrent symptoms, especially neurologic abnormalities associated with periods of decompensation. Routine laboratory tests, including measurement of plasma ammonia concentrations, can indicate a potential UCD; however, specific metabolic testing and ultimately enzymatic or molecular confirmation are necessary to establish a diagnosis. Treatment with dietary protein restriction and medications may be challenging in children.

Nitric oxide synthesis in ornithine transcarbamylase deficiency: possible involvement of low no synthesis in clinical manifestations of urea cycle defect

Nitric oxide (NO) levels in plasma and urine were determined in 5 girls with ornithine transcarbamylase deficiency (OTCD) of late-onset type, who often developed migraine-like headache or vomiting. The patients were found to have low NO synthesis, suggesting that the low NO synthesis contributes to the clinical manifestations of urea cycle defect.

Comparison of clinical, magnetic resonance and evoked potentials data in a case of valproic-acid-related hyperammonemic coma

Magnetic resonance (MR) multimodality evoked potentials (MEPs) and clinical findings were correlated in a 47-year-old epileptic man in whom parenteral valproic acid (VPA) therapy induced severe comatose hyperammonemic encephalopathy without biological signs of hepatotoxicity (or hepatocytic dysfunction). Although the plasma VPA level remained within a normal therapeutic range, the ammoniemia increased to a toxic peak level at 411 micromol/l 24 h after symptom onset, requiring VPA therapy discontinuation. Brain MR monitoring demonstrated early cytotoxic edema evolving into delayed vasogenic edema and final brain atrophy. Concomitantly to abnormalities within the brainstem on MR images, an increase in brainstem conduction at MEPs and clinical disturbance of brainstem reflexes were observed at the initial phase of the disease course. Later, the resolution of the MR and MEPs abnormalities paralleled the clinical recovery of the reflexes.

Acute extrapyramidal syndrome in mild ornithine transcarbamylase deficiency: metabolic stroke involving the caudate and putamen without metabolic decompensation

A 6-year-old male with partial ornithine transcarbamylase (OTC) deficiency had acute and rapidly progressive symmetrical swelling of the head of the caudate nuclei and putamina. Clinical presentation was ataxia and dysarthria progressing to seizures and coma; these symptoms gradually resolved with supportive management. Although he had been recently treated for mild hyperammonemia, there was no evidence of acute metabolic decompensation prior to presentation, and plasma ammonia and amino acids were consistent with good metabolic control. This case is novel in that the neurological insult affected the neostriatum of the basal ganglia and the episode occurred in the absence of an apparent metabolic abnormality, unique observations in a patient with OTC deficiency.

CONCLUSION

This case suggests that the pathophysiology of metabolic stroke is complicated. It also argues for an evaluation for metabolic stroke in patients with known inborn errors of metabolism who present with unusual neurological symptoms in the absence of biochemical abnormalities. Similarly, this case suggests that patients presenting with unexplained neurological insults might benefit from an evaluation for an inborn error of metabolism.

Magnetic resonance imaging in late-onset ornithine transcarbamylase deficiency

We examined brain magnetic resonance imaging (MRI) in a cohort of seven patients with ornithine transcarbamylase deficiency (OTCD), and correlated MRI findings with clinical manifestations. Seven patients with OTCD, aged 3-27 years, all with a missense mutation, were involved in the study. We classified the OTCD patients clinically into four stages. MR study was performed with a 1.5-T superconducting magnet during asymptomatic periods. MRI revealed white matter lesions in two patients with an advanced clinical stage, i.e. T1 and T2 prolongated round lesions in the deep white matter and posterolateral angle of the lateral ventricle in one patient; small foci of T2 and T1 prolongation in the subcortical white matter in another. Parenchymal lesions, and cerebral and cerebellar atrophy were not found in the other five patients. MRI might be normal in the early stage of the disease, and progress in proportion to the clinical stage of OTCD. OTCD should be considered as a differential diagnosis of small foci in the white matter in children.

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.

Ornithine transcarbamylase deficiency in females: an often overlooked cause of treatable encephalopathy

Ornithine transcarbamylase deficiency is an X-linked recessive disorder of urea biosynthesis characterized by recurrent, often fatal, hyperammonemic encephalopathy in affected males; carrier females are usually asymptomatic. We report here the clinical and laboratory findings in five symptomatic heterozygous females with ornithine transcarbamylase deficiency. In each case, the onset of symptoms occurred in the 1st year of life, but diagnosis was delayed by up to 15 years. Symptoms included recurrent vomiting with lethargy (five patients), dietary protein intolerance (five), irritability (four), severe acute encephalopathy (three), ataxia (three), and acute hemiparesis (two). All eventually showed evidence of developmental delay or learning difficulties. Two of the three who experienced severe, acute, hyperammonemic encephalopathy suffered serious, permanent neurologic sequelae. Three of the patients showed decreased ornithine transcarbamylase activity in liver obtained by needle biopsy, and the other two had marked orotic aciduria associated with hyperammonemia. Neuroimaging studies demonstrated persistent abnormal lobar attenuation and abnormal signal on computed tomographic scan and magnetic resonance imaging. All patients showed marked symptomatic improvement on treatment with dietary protein restriction supplemented by pharmacologic measures to increase nonprotein nitrogen excretion. Ornithine transcarbamylase deficiency should be considered in the differential diagnosis of acute or chronic encephalopathy in females at any age.