Arginase deficiency

Potential role of ARG1 c.57G > A variant in Argininemia

BACKGROUND AND OBJECTIVE

Argininemia (OMIM: 207800), as well as arginase deficiency, a disorder of the urea cycle caused by deficiency of arginase 1 (ARG1, NP_000036.2), is a scarce autosomal recessive genetic disease. The patients who suffered with argininemia often showed spastic paraplegia, epileptic seizures, severe mental retardation, and even the hyperammonemia. In neonatal screening, we found a healthy baby with mild elevated arginine levels. We have demonstrated the genetic etiology of the patient.

METHODS

The patient's clinical characteristic and family history were collected. The technologies including Next Generation Sequencing (NGS), Sanger sequencing, Bioinformatics Analysis, RNA extraction, cDNA obtained, Sanger sequencing, Minigene splicing assay, Real-time PCR, Single-molecule real-time (SMRT) sequencing were applied.

RESULTS

One homozygous variant, c.57G > A (p.Q19=), was identified in the proband, which was inherited from the parents. Through different detection methods, we found that the c.57G > A variant causes three different transcriptional versions: normal mRNA (mRNA from blood), mRNA with the exon2 deletion (73bp, mRNA from blood and minigene assay), and mRNA sequence from the SMRT sequencing (parts of exons and introns were detected, including exon 1-4, intron 1 and 4, and part of intron 2, 3, and 5). The expression of ARG1 mRNA and protein also decreased in the blood. The related genes of NMD (Nonsense-mediated mRNA decay), SMG1, UPF1, and UPF3b, were expressed higher than the controls in the blood, which hints the NMD could play a role in the mRNA decay regarding the cDNA with 73bp deletion by c.57G > A variant.

CONCLUSIONS

The study is the first study considering a synonymous variant of the ARG1 gene influencing alternative splicing(AS). Otherwise, the variant c.57G > A is relatively frequent in the general population( MAF = 0.0146). Our discovery revealed the variant possesses partial pathogenic potential, which would contribute to the deeper understanding and gold model for the intricate relationship between genetic mutations, arginine metabolism, and physical function.

Hyperargininemia Experiences over Last 7 Years from a Tertiary Care Center

Context

Several Enzymes carry out chemical reactions for the production of energy and carrying out normal functioning of the organism. Disorders of these functions can result in permanent damage to the child affecting multiple systems. Most metabolic disorders are at least controllable and therefore it is important to recognize them early for ensuring optimum growth and development. This involves proper pattern recognition by the clinician.

Aims

In this study we are discussing a rare treatable metabolic disorder namely Hyperargininemia seen by the authors in the last seven years.

Settings and Design

Various parameters of confirmed hyperargininemia patients were analysed.

Methods and Material

It is a descriptive study where all patients were confirmed cases with red blood cell arginase levels <10.

Statistical Analysis used

Descriptive statistical analysis, Mann-whitney test, spearman's rho.

Results

In this study we found consanguinity in 30 % of patients. At least one sibling was affected in 13 % of patients. Females were more in this group though the pattern remains AR. Symptom onset showed variability from less than 1 year to up to 17 years. Commonest clinical feature was cognitive dysfunction, spasticity, seizures, microcephaly and lesser number with extrapyramidal and cerebellar features. Failure to thrive and dysmorphic features were also seen.

Conclusion

Hyperargininemia commonly manifests as regression, failure to thrive, spasticity, seizures with or without microcephaly. When the above phenotype is seen, it is mandatory to screen for urea cycle disorders.

Impacts of lisinopril and lisinopril plus simvastatin on erythrocyte and plasma arginase, nitrite, and nitrate in hypertensive patients

Angiotensin-converting enzyme inhibitors are effective at reducing blood pressure, whereas statins decrease plasma cholesterol, impeding atherosclerosis. The authors hypothesize that these medications may improve blood pressure by modifying the arginase-nitric oxide synthase system of erythrocytes. In this study, the effects of lisinopril alone versus lisinopril + simvastatin on erythrocyte and plasma arginase enzyme and nitric oxide metabolites are compared. Patients with atherosclerosis and hypertension are randomly assigned to receive lisinopril 10 to 20 mg/d or lisinopril 10 to 20 mg/d plus simvastatin 20 mg/d for 24 weeks. Higher arginase activity is observed in erythrocytes from 100% of patients and mainly recovered after 12 and 24 weeks of treatment with lisinopril or lisinopril + simvastatin. Plasma arginase activity is 3 orders of magnitude lower than erythrocyte arginase activity in all participants, suggesting a lack of its clinical significance. Both treatments cause the increase in plasma $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ , $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ , and $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ in 100% of patients. Erythrocyte $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ concentration is greatly decreased in hypertensive patients but recovers after monotherapy and combined therapy. The results show for the first time that lisinopril monotherapy and combined lisinopril + simvastatin therapy exhibit pronounced and equipotential normalizing effects on erythrocyte arginase and nitric oxide synthase activities.

Inborn errors of metabolism: the flux from Mendelian to complex diseases

Inborn errors of metabolism are characterized by dysregulation of the metabolic networks that underlie development and homeostasis, and constitute an important and expanding group of genetic disorders in humans. Diagnostic methods that are based on molecular genetic tools have a limited ability to correlate phenotypes with subtle changes in metabolic fluxes. We argue that the direct and dynamic measurement of metabolite flux will facilitate the integration of environmental, genetic and biochemical factors with phenotypic information. Ultimately, this integration will lead to new diagnostic and therapeutic approaches that are focused on the manipulation of these pathways.