Ornithine transcarbamylase deficiency: a urea cycle defect

Presentation of an acquired urea cycle disorder post liver transplantation

The liver's role as the largest organ of metabolism and the unique and often critical function of liver-specific enzyme pathways imply a greater risk to the recipient of acquiring a donor metabolic disease with liver transplants versus other solid organ transplants. With clinical consequences rarely reported, the frequency of solid organ transplant transfer of metabolic disease is not known. Ornithine transcarbamylase deficiency (OTCD), although rare, is the most common of the urea cycle disorders (UCDs). Because of phenotypic heterogeneity, OTCD may go undiagnosed into adulthood. With over 5000 liver transplant procedures annually in the United States, the likelihood of unknowingly transmitting OTCD through liver transplantation is very low. We describe the clinical course of a liver transplant recipient presenting with acute hyperammonemia and encephalopathy after receiving a liver graft form a donor with unrecognized 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.

Foxp3 controls autoreactive T cell activation through transcriptional regulation of early growth response genes and E3 ubiquitin ligase genes, independently of thymic selection

To elucidate the mechanisms of autoreactive T cell activation and expansion, we used endogenous viral superantigens (VSAg)-reactive T cells as a model of self-antigens in two strains of Foxp3-mutant mice. These two strains, together with wild-type mice, provided us with an advantage to simultaneously study the positively and negatively selected as well as rescued autoreactive T cells. We show here that while both VSAg-reactive and non-VSAg-reactive T cells are equally activated in Foxp3-mutant mice, only the VSAg-reactive T cells are preferentially expanded independently of their selected states in the thymus. The T cell activation appears to be controlled by Foxp3 through transcriptional regulation of early growth response (Egr) genes Egr-2 and Egr-3, and E3 ubiquitin (Ub) ligase genes Cblb, Itch and GRAIL, subsequently affecting degradation of two key signaling proteins, PLCgamma1 and PKC-theta. Physiologically, the positively, but not negatively selected VSAg-reactive T cells are spontaneously activated without significant expansion. The results suggest that autoreactive T cell activation is controlled by Foxp3 through transcriptional regulation of early growth response genes and E3 ubiquitin ligase genes, independently of thymic selection.

Fatal cerebral edema from late-onset ornithine transcarbamylase deficiency in a juvenile male patient receiving valproic acid

OBJECTIVES

The aims of this report are to 1) present a rare case of fatal cerebral edema associated with late-onset ornithine transcarbamylase (OTC) deficiency in a juvenile male patient receiving valproic acid and 2) review the neuropathologic changes associated with the hyperammonemia.

DESIGN

Case report.

SETTING

A community hospital and a tertiary pediatric critical care unit.

INTERVENTIONS

Carbohydrate administration, intravenous nitrogen excretion cocktail, and high-flux hemodialysis.

MEASUREMENTS AND MAIN RESULTS

Despite aggressive therapy for presumed late-onset OTC deficiency, the patient rapidly developed fatal cerebral edema with tonsillar herniation. A liver biopsy confirmed OTC deficiency with approximately 3% of residual hepatic enzyme activity. Chromosomal analysis showed a normal male karyotype. A thorough molecular analysis of the coding region in the OTC gene Xp21.1 was completed, but mutations were not identified, suggesting an upstream or downstream abnormality. Severe brain swelling was evident on neuropathology, and histopathology showed Alzheimer type II astrocytes, neuronal cytoplasmic changes, and hypertrophy and eosinophilia of the small arterial walls.

CONCLUSIONS

OTC deficiency is the most common urea cycle defect causing hyperammonemia. Late-onset presentations of OTC are infrequent, primarily affecting female patients. We present a rare case of a late-onset OTC deficiency in a juvenile male patient receiving valproic acid therapy who developed fatal cerebral edema. Valproic acid exacerbates acute elevations in ammonia and may contribute synergistically with ammonia to cerebral mitochondrial dysfunction.

Anesthetic management of patients with ornithine transcarbamylase deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common inborn error of the urea cycle. Several specific factors require care during anesthesia in patients with this condition to avoid metabolic decompensation with acute hyperammonemia and encephalopathy. We report monozygous twins with severe neonatal-onset OTCD undergoing general anesthesia twice each, with midazolam, s-ketamine, fentanyl and isoflurane in combination with surgical field infiltration with ropivacaine. Alternative pathway medication and high-caloric diet with 10% glucose solutions were continuously administered during the perioperative course. Both children were extubated within 10 min of the final suture, and their neurological state remained unchanged. Perioperatively, blood ammonia levels remained within the normal range.

Der Patient mit Ornithintranscarbamylasemangel

Ornithine transcarbamylase deficiency (OTCD) is the most common inborn urea cycle disorder. Patients with OTCD are at risk of acute metabolic decompensation with hyperammonemia and subsequent encephalopathy, coma and death. Symptoms may be triggered by infections, drugs and stress, evoked by trauma, pain, fear, surgery and anaesthesia or by episodes of protein catabolism, i.e. fasting-induced, post partum or during gastrointestinal bleeding. Several specific considerations must be made for anaesthetic and intensive care management in patients with this disease in order to avoid metabolic decompensation. We report the intensive care management of the first manifestation of late-onset OTCD in a 16-year-old girl and a course of inconspicuous general anaesthesia with midazolam, s-ketamine, fentanyl and isoflurane in a 22-year-old girl with known OTCD.