Hyperammonemia in a Woman with Late-onset Ornithine Transcarbamylase Deficiency

Non-producer multiple myeloma presenting with acute hyperammonemic encephalopathy: case report

BACKGROUND

Hyperammonemic encephalopathy (HE) is a rare and life-threatening complication of multiple myeloma, with underlying mechanisms that are not fully understood. In contrast to previously reported cases, most of which have been associated with IgG or IgA isotypes, we describe a patient with HE as the presenting symptom of non-producer multiple myeloma (NPMM).

CASE PRESENTATION

A 60-year-old man developed lethargy that progressed into coma. He was found to have an elevated ammonia level, despite normal hepatic function. He was diagnosed with HE secondary to NPMM, demonstrating 80% plasma cells without light chain expression in the bone marrow and absence of a monoclonal protein in the serum or urine, including by matrix-assisted laser desorption ionization time-of-flight mass-spectrometry (MASS-FIX). Myeloma-directed therapy with daratumumab, bortezomib, cyclophosphamide and dexamethasone successfully reversed his HE. At clinical relapse, he received salvage chemotherapy followed by venetoclax therapy, leading to a short period of neurological recovery.

CONCLUSIONS

This case demonstrates that HE can occur in a patient with NPMM and challenges the mechanism suggested by limited prior studies; i.e., that excess ammonia in multiple myeloma arises from degradation of M-proteins. We postulate that the neoplastic plasma cells in NPMM have amplified amino acid metabolism, despite lacking detectable intracellular or secreted immunoglobulins.

Hyperammonemia in a pregnant woman with citrullinemia type I: a case report and literature review

BACKGROUND

Citrullinemia type I (CTLN1) is a rare urea cycle disorder (UCD) with few adult cases described so far. Diagnosis of late-onset CTLN1 is difficult, and delayed treatment may increase the risk of severe hyperammonemia. Pregnancy is an important risk factor for women with CTLN1. However, the clinical manifestations of CTLN1 in a pregnant woman may be mistaken for pregnancy side effects and ultimately delay a timely diagnosis.

CASE PRESENTATION

A 34-year-old woman developed vomiting and disturbance of consciousness after 12 weeks of gestation. A blood test showed hyperammonemia (454 μg/dL) with normal liver function tests. She fell into a deep coma, and her serum ammonia level increased to 800 μg/dL. Continuous renal replacement therapy (CRRT) was administered as a diagnostic treatment for UCD and serum ammonia. This patient's case was complicated by co-infection; her dependents decided to withdraw life support and the patient died. She was diagnosed with CTLN1 by analyses of plasma amino acids, urinary orotic acid, and second-generation gene sequencing.

DISCUSSION AND CONCLUSION

When a patient displays symptoms of emesis and disturbance of consciousness in early pregnancy, blood ammonia should be monitored, and UCD should be considered, particularly for patients with hyperammonemia in the absence of severe liver function abnormalities.

Psychological Stress Triggers a Hyperammonemia Episode in Patient with Ornithine Transcarbamylase Deficiency

An 18-year-old male motorcycle racer, who was a participant in the FIM Road Racing World Championship and had a history of Ornithine Transcarbamylase deficiency, developed nausea and dizziness while driving his motorcycle and became unconscious right after he stopped at the box. He was rapidly attended to by the medical personnel of the circuit, and once he recovered consciousness, he was taken to the local hospital where the blood analysis showed hyperammonemia (307 μg/dL) and excess alkalosis. The patient was properly following the prescribed treatment, and there were no environmental stressors. Hence, psychological stress and its somatization due to the risky task that the patient was performing could have triggered the episode. Stress must be considered as a potential cause, triggering strenuous metabolic stress that leads to hyperammonemia.

Corticosteroid suppresses urea-cycle-related gene expressions in ornithine transcarbamylase deficiency

Background

Ornithine transcarbamylase deficiency (OTCD) is most common among urea cycle disorders (UCDs), defined by defects in enzymes associated with ureagenesis. Corticosteroid administration to UCD patients, including OTCD patients, is suggested to be avoided, as it may induce life-threatening hyperammonemia. The mechanism has been considered nitrogen overload due to the catabolic effect of corticosteroids; however, the pathophysiological process is unclear.

Methods

To elucidate the mechanism of hyperammonemia induced by corticosteroid administration in OTCD patients, we analyzed a mouse model by administering corticosteroids to OTC^spf−ash mice deficient in the OTC gene. Dexamethasone (DEX; 20 mg/kg) was administered to the OTC^spf−ash and wild-type (WT) mice at 0 and 24 h, and the serum ammonia concentrations, the levels of the hepatic metabolites, and the gene expressions related with ammonia metabolism in the livers and muscles were analyzed.

Results

The ammonia levels in Otc^spf−ash mice that were administered DEX tended to increase at 24 h and increased significantly at 48 h. The metabolomic analysis showed that the levels of citrulline, arginine, and ornithine did not differ significantly between Otc^spf−ash mice that were administered DEX and normal saline; however, the level of aspartate was increased drastically in Otc^spf−ash mice owing to DEX administration (P < 0.01). Among the enzymes associated with the urea cycle, mRNA expressions of carbamoyl-phosphate synthase 1, ornithine transcarbamylase, arginosuccinate synthase 1, and arginosuccinate lyase in the livers were significantly downregulated by DEX administration in both the Otc^spf−ash and WT mice (P < 0.01). Among the enzymes associated with catabolism, mRNA expression of Muscle RING-finger protein-1 in the muscles was significantly upregulated in the muscles of WT mice by DEX administration (P < 0.05).

Conclusions

We elucidated that corticosteroid administration induced hyperammonemia in Otc^spf−ash mice by not only muscle catabolism but also suppressing urea-cycle-related gene expressions. Since the urea cycle intermediate amino acids, such as arginine, might not be effective because of the suppressed expression of urea-cycle-related genes by corticosteroid administration, we should consider an early intervention by renal replacement therapy in cases of UCD patients induced by corticosteroids to avoid brain injuries or fatal outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-022-02213-0.

Fifteen years of urea cycle disorders brain research: Looking back, looking forward

Urea cycle disorders (UCD) are inherited diseases resulting from deficiency in one of six enzymes or two carriers that are required to remove ammonia from the body. UCD may be associated with neurological damage encompassing a spectrum from asymptomatic/mild to severe encephalopathy, which results in most cases from Hyperammonemia (HA) and elevation of other neurotoxic intermediates of metabolism. Electroencephalography (EEG), Magnetic resonance imaging (MRI) and Proton Magnetic resonance spectroscopy (MRS) are noninvasive measures of brain function and structure that can be used during HA to guide management and provide prognostic information, in addition to being research tools to understand the pathophysiology of UCD associated brain injury. The Urea Cycle Rare disorders Consortium (UCDC) has been invested in research to understand the immediate and downstream effects of hyperammonemia (HA) on brain using electroencephalogram (EEG) and multimodal brain MRI to establish early patterns of brain injury and to track recovery and prognosis. This review highlights the evolving knowledge about the impact of UCD and HA in particular on neurological injury and recovery and use of EEG and MRI to study and evaluate prognostic factors for risk and recovery. It recognizes the work of others and discusses the UCDC's prior work and future research priorities.

Common polymorphic OTC variants can act as genetic modifiers of enzymatic activity

Understanding the role of common polymorphisms in modulating the clinical phenotype when they co‐occur with a disease‐causing lesion is of critical importance in medical genetics. We explored the impact of apparently neutral common polymorphisms, using the gene encoding the urea cycle enzyme, ornithine transcarbamylase (OTC), as a model system. Distinct combinations of genetic backgrounds embracing two missense polymorphisms were created in cis with the pathogenic p.Arg40His replacement. In vitro enzymatic assays revealed that the polymorphic variants were able to modulate OTC activity both in the presence or absence of the pathogenic lesion. First, we found that the combination of the minor alleles of polymorphisms p.Lys46Arg and p.Gln270Arg significantly enhanced enzymatic activity in the wild‐type protein. Second, enzymatic assays revealed that the minor allele of the p.Gln270Arg polymorphism was capable of ameliorating OTC activity when combined in cis with the pathogenic p.Arg40His replacement. Structural analysis predicted that the minor allele of the p.Gln270Arg polymorphism would serve to stabilize the OTC wild‐type protein, thereby corroborating the results of the experimental assays. Our findings demonstrate the potential importance of cis‐interactions between common polymorphic variants and pathogenic missense mutations and illustrate how standing genetic variation can modulate protein function.

Management of late onset urea cycle disorders-a remaining challenge for the intensivist?

Background

Hyperammonemia caused by a disorder of the urea cycle is a rare cause of metabolic encephalopathy that may be underdiagnosed by the adult intensivists because of its rarity. Urea cycle disorders are autosomal recessive diseases except for ornithine transcarbamylase deficiency (OTCD) that is X-linked. Optimal treatment is crucial to improve prognosis.

Main body

We systematically reviewed cases reported in the literature on hyperammonemia in adulthood. We used the US National Library of Medicine Pubmed search engine since 2009. The two main causes are ornithine transcarbamylase deficiency followed by type II citrullinemia. Diagnosis by the intensivist remains very challenging therefore delaying treatment and putting patients at risk of fatal cerebral edema. Treatment consists in adapted nutrition, scavenging agents and dialysis. As adults are more susceptible to hyperammonemia, emergent hemodialysis is mandatory before referral to a reference center if ammonia levels are above 200 µmol/l as the risk of cerebral edema is then above 55%. Definitive therapy in urea cycle abnormalities is liver transplantation.

Conclusion

Awareness of urea cycle disorders in adults intensive care units can optimize early management and accordingly dramatically improve prognosis. By preventing hyperammonemia to induce brain edema and herniation leading to death.