Clinical status, biochemical profile and management of a single cohort of patients with arginase deficiency

Unraveling the Link: Seizure Characteristics and Ammonia Levels in Urea Cycle Disorder During Hyperammonemic Crises

BACKGROUND

This retrospective clinical study performed at a single clinical center aimed to identify the prevalence of seizures in individuals with urea cycle disorders (UCDs) with and without hyperammonemic (HA) crises. In addition, we sought to correlate the utility of biochemical markers and electroencephalography (EEG) in detecting subclinical seizures during HA.

METHODS

Medical records of individuals with UCDs enrolled in Urea Cycle Disorders Consortium Longitudinal Study (UCDC-LS) (NCT00237315) at Children's National Hospital between 2006 and 2022 were reviewed for evidence of clinical and subclinical seizuress during HA crises, and initial biochemical levels concurrently.

RESULTS

Eighty-five individuals with UCD were included in the analyses. Fifty-six of the 85 patients (66%) experienced HA crises, with a total of 163 HA events. Seizures are observed in 13% of HA events. Among all HA events with concomitant EEG, subclinical seizures were identified in 27% of crises of encephalopathy without clinical seizures and 53% of crises with clinical seizures. The odds of seizures increases 2.65 (95% confidence interval [CI], 1.51 to 4.66) times for every 100 μmol/L increase in ammonia and 1.14 (95% CI, 1.04 to 1.25) times for every 100 μmol/L increase in glutamine.

CONCLUSIONS

This study highlights the utility of EEG monitoring during crises for patients presenting with clinical seizures or encephalopathy with HA. During HA events, measurement of initial ammonia and glutamine can help determine risk for seizures and guide EEG monitoring decisions.

Plasma arginine levels in arginase deficiency in the "real world"

Background

Deficiency of arginase-1, the final enzyme in the urea cycle, causes a distinct clinical syndrome and is characterized biochemically by a high level of plasma arginine. While conventional therapy for urea cycle disorders can lower these levels to some extent, it does not normalize them. Until now, research on plasma arginine levels in this disorder has primarily relied on data from specialized tertiary centers, which limits the ability to assess the natural history and treatment efficacy of arginase-1 deficiency due to the small number of patients in each center and technical variations in plasma arginine measurements among different laboratories.

Method

In this study, we reported plasma arginine levels from 51 patients with arginase-1 deficiency in the database of Quest Diagnostics. The samples were collected from different US regions.

Results

The mean plasma arginine level in these treated patients was 373 μmol/L and the median level was 368.4 μmol/L. Our data set from 30 arginase deficiency patients with plasma amino acid data from five or more collections revealed significant correlations between the levels of arginine and five other amino acids (citrulline, alanine, ornithine, glutamine, and asparagine).

Conclusion

Despite treatment, the arginine levels remained persistently elevated and did not change significantly with age, suggesting the current treatment regimen is inadequate to control arginine levels and underscoring the need to seek more effective treatments for this disorder.

The role and control of arginine levels in arginase 1 deficiency

Arginase 1 Deficiency (ARG1-D) is a rare urea cycle disorder that results in persistent hyperargininemia and a distinct, progressive neurologic phenotype involving developmental delay, intellectual disability, and spasticity, predominantly affecting the lower limbs and leading to mobility impairment. Unlike the typical presentation of other urea cycle disorders, individuals with ARG1-D usually appear healthy at birth and hyperammonemia is comparatively less severe and less common. Clinical manifestations typically begin to develop in early childhood in association with high plasma arginine levels, with hyperargininemia (and not hyperammonemia) considered to be the primary driver of disease sequelae. Nearly five decades of clinical experience with ARG1-D and empirical studies in genetically manipulated models have generated a large body of evidence that, when considered in aggregate, implicates arginine directly in disease pathophysiology. Severe dietary protein restriction to minimize arginine intake and diversion of ammonia from the urea cycle are the mainstay of care. Although this approach does reduce plasma arginine and improve patients' cognitive and motor/mobility manifestations, it is inadequate to achieve and maintain sufficiently low arginine levels and prevent progression in the long term. This review presents a comprehensive discussion of the clinical and scientific literature, the effects and limitations of the current standard of care, and the authors' perspectives regarding the past, current, and future management of ARG1-D.