Urea Cycle Disorders: Diagnosis and Management

Urea cycle disorders comprise a group of inherited metabolic conditions characterised by deficiencies in one of six core enzymes or associated transporters responsible for converting ammonia to urea. Impaired function leads to hyperammonaemia, which can precipitate neurological injury, hepatic dysfunction and multisystem complications. Clinical presentations range from severe neonatal crises with lethargy, encephalopathy and risk of early mortality, to late‐onset or non‐classical forms manifesting in adolescence or adulthood with neurocognitive deficits and episodic metabolic decompensation. Diagnostic strategies combine biochemical profiling—plasma ammonia, amino acid analysis and urinary organic acids—with genetic testing to confirm enzyme defects. Rapid recognition is critical, especially in acute hyperammonaemic episodes, where interventions include ammonia scavengers, dietary protein restriction supplemented with essential amino acids, and supportive extracorporeal therapies. Long‐term management encompasses individualised nutrition plans, pharmacological agents that promote alternative nitrogen excretion pathways, and, in selected cases, orthotopic liver transplantation. Emerging modalities, such as enzyme replacement and gene therapy, hold promise for more targeted correction of underlying enzyme deficits. Multidisciplinary care and newborn screening initiatives have improved survival, yet neurological sequelae remain a significant burden, underscoring the need for early diagnosis and optimised therapeutic regimens.

Research from Nature Portfolio

Recent work has elucidated the molecular basis of enzyme regulation within the urea cycle. High‐resolution structural analyses have revealed how allosteric activators induce conformational switches in key enzymes, clarifying the impact of pathogenic variants on catalytic efficiency and informing the design of small‐molecule modulators. In the field of acute management, expert consensus recommendations now advocate for stratified use of extracorporeal clearance techniques and non‐renal replacement therapies in paediatric patients presenting with hyperammonaemia, detailing thresholds for peritoneal dialysis, continuous therapies or intermittent haemodialysis based on ammonia levels and neurological status. Advances in gene delivery approaches have demonstrated that combined hepatic and neuronal correction can address both ammonia detoxification and nitric oxide dysregulation, restoring metabolic homeostasis in preclinical models and reducing neurotoxicity more effectively than single‐organ interventions.

Urea Cycle Disorders: Diagnosis and Management publication trend

The graph below shows the total number of articles in urea cycle disorders: diagnosis and management across all publications each year (not limited to Nature Index journals).

Technical terms

Urea cycle: A hepatic metabolic pathway converting toxic ammonia into urea for renal excretion.

Hyperammonaemia: Elevated blood ammonia levels that are neurotoxic if not rapidly controlled.

Alternative pathway therapy: Pharmacological strategy using ammonia scavengers to divert nitrogen into excretable metabolites independent of the urea cycle.

Enzyme replacement therapy: Administration of functional recombinant enzymes to compensate for endogenous deficiencies.

Kidney replacement therapy: Extracorporeal procedures (e.g. dialysis) employed to remove ammonia and other toxins during acute decompensation.

Blood–brain barrier: Selective endothelial interface regulating molecular exchange between the circulation and the central nervous system.

Nitric oxide: A signalling molecule involved in vascular regulation and neuronal function, whose synthesis can be disrupted in certain urea cycle disorders.

Gene therapy: Introduction of corrective genetic material to restore deficient enzyme activity at the cellular level.

References

1. Efficacy and safety of pegzilarginase in arginase 1 deficiency (PEACE): a phase 3, randomized, double-blind, placebo-controlled, multi-centre trial. EClinicalMedicine (2024).
2. Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression. JCI Insight (2023).
3. Suggested guidelines for the diagnosis and management of urea cycle disorders. Orphanet Journal of Rare Diseases (2012).
4. Structure of human carbamoyl phosphate synthetase: deciphering the on/off switch of human ureagenesis. Scientific Reports (2015).
5. Consensus guidelines for management of hyperammonaemia in paediatric patients receiving continuous kidney replacement therapy. Nature Reviews Nephrology (2020).
6. Argininosuccinic aciduria fosters neuronal nitrosative stress reversed by Asl gene transfer. Nature Communications (2018).