Hyperargininemia Experiences over Last 7 Years from a Tertiary Care Center

Natural history of epilepsy in argininosuccinic aciduria provides new insights into pathophysiology: A retrospective international study

OBJECTIVE

Argininosuccinate lyase (ASL) is integral to the urea cycle, which enables nitrogen wasting and biosynthesis of arginine, a precursor of nitric oxide. Inherited ASL deficiency causes argininosuccinic aciduria, the second most common urea cycle defect and an inherited model of systemic nitric oxide deficiency. Patients present with developmental delay, epilepsy, and movement disorder. Here we aim to characterize epilepsy, a common and neurodebilitating comorbidity in argininosuccinic aciduria.

METHODS

We conducted a retrospective study in seven tertiary metabolic centers in the UK, Italy, and Canada from 2020 to 2022, to assess the phenotype of epilepsy in argininosuccinic aciduria and correlate it with clinical, biochemical, radiological, and electroencephalographic data.

RESULTS

Thirty-seven patients, 1-31 years of age, were included. Twenty-two patients (60%) presented with epilepsy. The median age at epilepsy onset was 24 months. Generalized tonic-clonic and focal seizures were most common in early-onset patients, whereas atypical absences were predominant in late-onset patients. Seventeen patients (77%) required antiseizure medications and six (27%) had pharmacoresistant epilepsy. Patients with epilepsy presented with a severe neurodebilitating disease with higher rates of speech delay (p = .04) and autism spectrum disorders (p = .01) and more frequent arginine supplementation (p = .01) compared to patients without epilepsy. Neonatal seizures were not associated with a higher risk of developing epilepsy. Biomarkers of ureagenesis did not differ between epileptic and non-epileptic patients. Epilepsy onset in early infancy (p = .05) and electroencephalographic background asymmetry (p = .0007) were significant predictors of partially controlled or refractory epilepsy.

SIGNIFICANCE

Epilepsy in argininosuccinic aciduria is frequent, polymorphic, and associated with more frequent neurodevelopmental comorbidities. We identified prognostic factors for pharmacoresistance in epilepsy. This study does not support defective ureagenesis as prominent in the pathophysiology of epilepsy but suggests a role of central dopamine deficiency. A role of arginine in epileptogenesis was not supported and warrants further studies to assess the potential arginine neurotoxicity in argininosuccinic aciduria.

Arginase 1 Deficiency in Patients Initially Diagnosed with Hereditary Spastic Paraplegia

Background

Arginase 1 Deficiency (ARG1-D) is a rare autosomal recessive urea cycle disorder (UCD) characterized by pathologic elevation of plasma arginine and debilitating manifestations. Based on clinical commonalities and low disease awareness, ARG1-D can be diagnosed as hereditary spastic paraplegia (HSP), leading to treatment delays.

Cases

A Hispanic woman with unremarkable medical history experienced progressive lower-limb spasticity in her 20s and received a diagnosis of HSP. She developed significant gait abnormalities and is unable to walk without assistance. More recently, two Hispanic brothers with childhood-onset manifestations including lower-limb spasticity, developmental delays, and seizures presented with suspected HSP. All three patients were ultimately diagnosed with ARG1-D based on plasma arginine several-fold above normal levels and loss-of-function ARG1 variants. Disease progression occurred before ARG1-D was correctly diagnosed.

Literature Review

Retrospective analyses demonstrate that diagnostic delays in ARG1-D are common and can be lengthy. Because of clinical similarities between ARG1-D and HSP, such as insidious onset and progressive spasticity, accurate diagnosis of ARG1-D is challenging. Timely ARG1-D diagnosis is critical because this UCD is a treatable genetic cause of progressive lower-limb spasticity.

Conclusions

Arginase 1 Deficiency should be considered in HSP differential diagnosis until biochemically/genetically excluded, and should be routinely included in HSP gene panels.

Phenotypic Pleiotropy in Arginase Deficiency: A Single Center Cohort

Background

Arginase deficiency is considered a masquerader of diplegic cerebral palsy. The rarity of hyperammonemic crisis and the slowly progressive course has made it a unique entity among the urea cycle defects.

Objectives

The aim of our study is to describe the varied phenotypic spectrum of children with arginase deficiency.

Methodology

This retrospective study included children and adolescents aged <18 years with a biochemical or genetic diagnosis of arginase deficiency from May 2011 to May 2022. Data were collected from the hospital's electronic database. The clinical presentation, laboratory parameters at baseline and during metabolic decompensation, neuroimaging, electroencephalography findings, and molecular studies were analyzed.

Results

About 11 children from nine families with biochemically or genetically proven arginase deficiency were analyzed. The male: female ratio was 2.7:1. Consanguineous parentage was observed in all children. The median age at presentation was 36 months (Range: 5 months-18 years). All children with onset of symptoms in early childhood had a predominant delay in motor milestones of varying severity. Metabolic decompensation with encephalopathy occurred in all except two children (n = 9, 81.8%). Pyramidal signs were present in all patients and additional extrapyramidal signs in two children. Positive family history was present in four probands. Seizures occurred in all children. Epilepsy with electrical status in slow wave sleep and West syndrome was noted in three children. All children had elevated ammonia and arginine at the time of metabolic crisis. The spectrum of neuroimaging findings includes periventricular, subcortical, and deep white matter signal changes and diffusion restriction. The mean duration of follow-up was 38.6 ± 34.08 months. All patients were managed with an arginine-restricted diet and sodium benzoate with or without ornithine supplementation.

Conclusion

Spastic diparesis, recurrent encephalopathy, presence of family history, and elevated serum arginine levels must alert the clinician to suspect arginase deficiency. Atypical presentations in our cohort include frequent metabolic crises and epileptic encephalopathy. Early identification and management will ensure a better neurodevelopmental outcome.

Neurological Deterioration in Three Siblings: Exploring the Spectrum of Argininemia

Argininemia or hyperargininemia is a urea cycle disorder caused by deficiency of the enzyme arginase 1. It is inherited in an autosomal recessive fashion. It commonly leads to spastic diplegia in childhood, but other important features include cognitive deterioration and epilepsy. Unlike other disorders of the urea cycle, hyperammonemia is not prominent. The authors report three siblings with genetically proven argininemia who presented with diverse phenotypes but with spasticity being a common feature. Sibling 1 developed motor regression in early childhood, sibling 2 developed delayed motor milestones from early infancy, whereas sibling 3 had global developmental delay in late infancy after a period of normal development. All siblings had mild hyperammonemia only. Early recognition is imperative, not only to initiate ammonia scavenging therapy which may lead to definite clinical improvement, but also to provide genetic counselling.