Ornithine transcarbamylase deficiency in the newborn infant

Nonhepatic hyperammonemic encephalopathy due to undiagnosed urea cycle disorder

Ornithine transcarbamoylase deficiency is the most common inherited urea cycle disorder. In adults, its phenotypes are diverse. In asymptomatic patients with late presentations, symptom onset is often associated with a precipitating factor. We present a case of a woman with urea cycle disorder diagnosed after an acute peptic ulcer bleed and fasting.

Reduced Functional Connectivity of Default Mode and Set-Maintenance Networks in Ornithine Transcarbamylase Deficiency

Background and Purpose

Ornithine transcarbamylase deficiency (OTCD) is an X-chromosome linked urea cycle disorder (UCD) that causes hyperammonemic episodes leading to white matter injury and impairments in executive functioning, working memory, and motor planning. This study aims to investigate differences in functional connectivity of two resting-state networks—default mode and set-maintenance—between OTCD patients and healthy controls.

Methods

Sixteen patients with partial OTCD and twenty-two control participants underwent a resting-state scan using 3T fMRI. Combining independent component analysis (ICA) and region-of-interest (ROI) analyses, we identified the nodes that comprised each network in each group, and assessed internodal connectivity.

Results

Group comparisons revealed reduced functional connectivity in the default mode network (DMN) of OTCD patients, particularly between the anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC) node and bilateral inferior parietal lobule (IPL), as well as between the ACC/mPFC node and the posterior cingulate cortex (PCC) node. Patients also showed reduced connectivity in the set-maintenance network, especially between right anterior insula/frontal operculum (aI/fO) node and bilateral superior frontal gyrus (SFG), as well as between the right aI/fO and ACC and between the ACC and right SFG.

Conclusion

Internodal functional connectivity in the DMN and set-maintenance network is reduced in patients with partial OTCD compared to controls, most likely due to hyperammonemia-related white matter damage. Because several of the affected areas are involved in executive functioning, it is postulated that this reduced connectivity is an underlying cause of the deficits OTCD patients display in this cognitive domain.

Hyperammonemia in a patient with late-onset ornithine carbamoyltransferase deficiency

Ornithine carbamoyltransferase (OTC) deficiency is a urea cycle disorder that causes the accumulation of ammonia, which can lead to encephalopathy. Adults presenting with hyperammonemia who are subsequently diagnosed with urea cycle disorders are rare. Herein, we report a case of a late-onset OTC deficient patient who was successfully treated with arginine, benzoate and hemodialysis. A 59-yr-old man was admitted to our hospital with progressive lethargy and confusion. Although hyperammonemia was suspected as the cause of the patient's mental changes, there was no evidence of chronic liver disease. A plasma amino acid and urine organic acid analysis revealed OTC deficiency. Despite the administration of a lactulose enema, the patient's serum ammonia level increased and he remained confused, leading us to initiate acute hemodialysis. After treatment with arginine, sodium benzoate and hemodialysis, the patient's serum ammonia level stabilized and his mental status returned to normal.

Altered neural activation in ornithine transcarbamylase deficiency during executive cognition: an fMRI study

BACKGROUND

Ornithine transcarbamylase deficiency (OTCD) is an X-linked urea cycle disorder characterized by hyperammonemia resulting in white matter injury and impairments in working memory and executive cognition.

OBJECTIVE

To test for differences in BOLD signal activation between subjects with OTCD and healthy controls during a working memory task.

DESIGN, SETTING AND PATIENTS

Nineteen subjects with OTCD and 21 healthy controls participated in a case-control, IRB-approved study at Georgetown University Medical Center.

INTERVENTION

An N-back working memory task was performed in a block design using 3T functional magnetic resonance imaging.

RESULTS

In subjects with OTCD we observed increased BOLD signal in the right dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) relative to healthy age matched controls.

CONCLUSIONS

Increased neuronal activation in OTCD subjects despite equivalent task performance points to sub-optimal activation of the working memory network in these subjects, most likely reflecting damage caused by hyperammonemic events. These increases directly relate to our previous finding of reduced frontal white matter integrity in the superior extents of the corpus callosum; key hemispheric connections for these areas. Future studies using higher cognitive load are required to further characterize these effects.

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.

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.

An integrated approach to the diagnosis and prospective management of partial ornithine transcarbamylase deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common inherited urea cycle disorder, and is transmitted as an X-linked trait. Female OTCD heterozygotes exhibit wide clinical severities, ranging from being apparently asymptomatic to having the profound neurologic impairment observed in affected males. However, clinical and laboratory diagnosis of partial OTCD during asymptomatic periods is difficult, and correlation of phenotypic severity with either DNA mutation and/or in vitro enzyme activity is imprecise. Provocative testing, including protein load and allopurinol challenge used in the diagnosis of OTCD females, is not without risk and subject to both false positives and negatives. Although definitive when successful, DNA-based diagnosis is unable to detect mutations in all cases. We have previously used the ratio of isotopic enrichments of [(15)N]urea/[(15)N]glutamine ((15)N-U/G) derived from physiologic measurements of ureagenesis by stable isotope infusion as a sensitive index of in vivo urea cycle activity. We have now applied this method in combination with traditional biochemical testing to aid in the diagnosis of a symptomatic OTCD female in whom mutation in the ornithine transcarbamylase (OTC) gene was not found. The (15)N-U/G ratio in this patient showed that she had severe reduction of in vivo urea cycle activity on par with affected male subjects. This was correlated with partially deficient OTC activity in her liver, degree of orotic aciduria, and history of suspected recurrent hyperammonemic episodes before age 3. The measurement of in vivo urea cycle activity in combination with traditional biochemical indices optimizes a diagnostic approach to the at-risk partial OTCD patient, especially in those in whom molecular testing is unproductive. Together they contribute to the risk versus benefit considerations regarding the pursuit of medical therapy versus surgical, ie, orthotopic liver transplantation (OLT) therapy. The decision to resort to OLT in females with partial OTC activity is controversial, requiring consideration of phenotypic severity, failure of medical therapy, access to tertiary care centers experienced in the management of acute hyperammonemia, and social factors. In this patient, the use of in vivo and in vitro measures of urea cycle activity in conjunction with a consideration of her clinical history and medical-social situation led to a decision for OLT.

Menstrual cycle and gonadal steroid effects on symptomatic hyperammonaemia of urea-cycle-based and idiopathic aetiologies

We report two female patients, one with a known inborn error of ureagenesis and the other of unknown cause, in whom recurrent, transient episodes of severe hyperammonaemia increased in frequency and severity with sexual maturity and parturition. Both responded to ovarian steroids administered continuously to suppress ovulation and menstruation, and ultimately to simple hysterectomy. These studies suggest a new therapeutic approach to defective ureagenesis in female patients and a relationship between ammonia production or disposal and the menstrual cycle.

Sudden infant death syndrome. The role of putrefactive toxins in respiratory paralysis and cerebral coma

The Sudden Infant Death Syndrome (SIDS) is responsible for the death of 10,000 infants annually in the U.S.A. The cause of these deaths is not known; all SIDS infants studied died during sleep in a silent fashion and there are no specific lesions observable post mortem. It may be of significance, however, that nearly half of SIDS infants had a respiratory tract infection in the last two weeks of life while forty percent had bloody froth over their mouths when found, presumably pulmonary oedema fluid. It is hypothesis that improper feeding or diarrhoea may likewise be involved in SIDS and that enterotoxins from putrefactive products are the precipitating event in this syndrome.

Electroencephalographic findings in urea-cycle disorders

Eleven electroencephalograms in 4 infants with urea-cycle disorders were reviewed. All infants had one or more abnormal EEGs. The abnormalities consisted mainly of multiareal spikes, spike-waves, or sharp-and-slow-wave activity. In addition, one patient, a term infant, exhibited exaggerated spindle-delta bursts. This infant, and also one other at a similar age, had monorhythmic paroxysmal theta activity. Clinically, all patients had seizures shortly preceding abnormal EEGs. EEG alterations were encountered over a wide range of elevated serum ammonia levels. Normal EEGs occurred in the face of slightly elevated levels. It is concluded that epileptiform EEG alterations may be a characteristic manifestation of urea-cycle disorders.

X-linked dominant inherited diseases with lethality in hemizygous males

X-linked dominant inheritance with lethality in hemizygous males is a rare mode of inheritance. The three best-known disorders which seem to be inherited in this way, are incontinentia pigmenti (IP) Bloch-Sulzberger, oral-facial-digital I (OFD I) syndrome, and focal dermal hypoplasia (FDH syndrome, Goltz syndrome). It is the purpose of this article to give a review of the clinical and genetic aspects of the above-mentioned diseases and to add those disorders in which this mode of inheritance is discussed. These disorders are: X-linked chondrodysplasia punctata (CP), cervico-oculo-acusticus syndrome (Wildervanck syndrome, COA), congenital cataract with microcornea or slight microphthalmia, muscular dystrophy--hemizygous lethal, partial lipodystrophy with lipatrophic diabetes and hyperlipidemia, Aicardi syndrome, coxo-auricular syndrome, and Johanson-Blizzard syndrome. OTC deficiency is included in the study, although there is no lethality in utero, only in the neonatal period. A critical evaluation of the current literature is carried out.

Ultrastructure of hepatic mitochondria in a child with hyperornithinemia, hyperammonemia, and homocitrullinuria

Ultrastructural studies of hepatic tissue obtained at biopsy from a nine year old severely retarded boy with hyperornithinemia, hyperammonemia, and homocitrullinuria showed mitochondria of bizarre shapes and unusual internal features. Among the latter were tubules extending throughout the length of the large mitochondria that on cross section had a rosette-like arrangement; the presence of a periodic, approximately 300 A thick, sievelike membrane interposed between the tubules and the inner mitochondrial membrane; and "bulges" of mitochondrial matrix occasionally formed between these two membranes. Since to be metabolized ornithine must enter the mitochondria, the hyperornithinemia is regarded as a reflection of its inability to reach the mitochondrial interior. It is speculated that among other possible causes, the unusual sievelike membrane may be the barrier to ornithine's access to the mitochondrion.

Treatment of hyperammonemic coma caused by inborn errors of urea synthesis

The relative effectiveness of exchange transfusion, peritoneal dialysis, arginine, and sodium benzoate was evaluated during 44 episodes of hyperammonemic coma in 31 patients with congenital urea cycle enzymopathies. The overall survival rate was 56%. In 15 episodes treated with EXT the fall in ammonium was 19 +/- 24%, P > 0.05. In 30 episodes treated with PD, the fall in ammonium was 60 +/- 9%, P < 0.001. Ten times more nitrogen was removed as glutamine than as ammonium during dialysis, suggesting that the effectiveness of PD resides in the removal of glutamine, glutamate, and alanine as well as ammonium. Prior to therapy all patients had hypoargininemia (18 +/- 2 microM); they responded to arginine supplementation with a rise in plasma arginine concentration to normal. In patients with AL deficiency, arginine supplementation (4 mmol/kg/day) was associated with a fall in ammonium level from 917 +/- 62 to 103 +/- 18 microM within 24 hours. When sodium benzoate (250 mg/kg/day) was used during eight episodes of coma, six patients responded with a significant decrease in plasma ammonium.

Transient hyperammonemia of the preterm infant

We report on five preterm infants (34 to 36 weeks' gestation) in whom an overwhelming illness developed within the first 48 hours of life. Each had mild respiratory distress that progressed within 48 hours to deep coma requiring ventilatory assistance. Ammonia concentrations in the plasma ranged from 844 to 7640 microgram per deciliter. Four received exchange transfusion and peritoneal dialysis; ammonia values returned to the normal range (less than 150 mug per deciliter) within 72 hours and remained there even after protein challenge. These four subsequently fed and developed normally. The fifth infant died without an attempt to lower plasma ammonia. In this infant (and two of the others) urea-cycle enzymes measured in liver tissue were in the normal range. Transient hyperammonemia of unknown cause may be a relatively common variety of neonatal hyperammonemia; it responds well to prompt diagnosis and aggressive therapy.

Attempted dietary treatment of a boy with hyperammonemia due to ornithine transferase deficiency

Dietary treatment of a male patient suffering from the delayed-onset type of OCT deficiency was attempted. Control of the hyperammonemia was attempted by restriction of protein intake, guided by monitoring the plasma ammonia and regular checking of the serum amino acid levels. The influence of supplementary citric acid or lactulose therapy on the plasma ammonia level was investigated and found to be negligible. The therapeutic effect of supplying ornithine and arginine (an essential amino acid in urea cycle disorders) is described. Despite intensive dietary treatment over two and a half years, a incorrigible hyperammonemic crisis resulted in the sudden death of our patient.

Assay of ornithine carbamoyltransferase activity in human liver using carbon-labeled ornithine and thin-layer chromatography

Ornithine carbamoyltransferase (EC 2.1.3.3) activity in human liver homogenates has been measured using 14C-labeled ornithine and unlabeled carbamoyl phosphate. A thin-layer chromatographic (TLC) procedure is used to separate the radioactive substrate and product, ornithine and citrulline, respectively, and the regions of the chromatogram corresponding to ornithine and citrulline are cut out and counted in a liquid scintillation spectrophotometer. The method has the following advantages: (1) the radioactive substrate ornithine is more stable in solution than carbamoyl phosphate, (2) 14C-labeled ornithine is available in higher specific activity than carbamoyl phosphate, (3) all radioactivity may be accounted for by using the TLC system, (4) the developed thin-layer chromatogram is stable indefinitely, (5) in contrast to colorimetric assays, other compounds in the raction mixture do not interfere with the citrulline determination, and (6) most importantly, the rate of the enzyme reaction at various time intervals can be determined by taking aliquots from the same incubation tube.

Urea-cycle enzyme deficiencies and an increased nitrogen load producing hyperammonemia in Reye's syndrome

Assay of urea-cycle enzymes in liver tissue showed ornithine transcarbamylase activities of 18 to 72 per cent of the normal mean in eight patients with Reye's syndrome, below the range of normal in seven of eight, and, in six cases, as low as those in females with X-linked deficiency of this enzyme. Carbamyl phosphate synthetase activities were less than 32 per cent of controls in two patients. Argininosuccinate synthetase and lyase activities were normal in seven patients. Arginase was normal in two biopsy specimens, but below normal in four of five autopsy specimens. The Km's for ornithine and carbamyl phosphate, pH optimum, and heat lability of ornithine transcarbamylase were normal. Two patients excreted 0.64 and 0.58 g per kilogram per day of urinary nitrogen at the peak of hyperammonemia, in spite of peritoneal dialysis. The hyperammonemia of Reye's syndrome apparently results from excess waste nitrogen that overwhelms the ability of reduced ornithine transcarbamylase (and occasionally carbamyl phosphate synthetase) to detoxify the ammonia load.

Hereditary ornithine transcarbamylase deficiency. Report of two male cases with residual enzymatic activity

The authors report two male cases of liver ornithine carbamyl transferase deficiency. In one the disease occurred at 8 years of age with hyperammoniemic coma leading to death in 48 hours. In the second case, symptoms appeared on the sixth day of life but the outcome was favorable. The child is normal at 15 months. In both cases, there was a residual 6-10% OCT activity. These observations are similar to two other male cases in the literature and are different from the male neonatal fatal form in which the deficiency is virtually total. They underline the genetically heterogeneous nature of OCT deficiencies and the fact that in this X-transmitted trait, hemizygotes can preserve a functional enzymatic activity compatible with life.