Impact of enteral arginine supplementation on lysine metabolism in humans: A proof-of-concept for lysine-related inborn errors of metabolism

Dietary management for pyridoxine-dependent epilepsy due to α-aminoadipic semialdehyde dehydrogenase deficiency, a follow-on from the international consortium guidelines

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is a neurometabolic disorder in the lysine metabolism pathway. In 2014 and 2021, the International PDE consortium published consensus guidelines about diagnosis and management. In this follow-on, a literature review was performed and nutrition management was evaluated through an international dietary questionnaire with 40 respondents. This manuscript discusses consensus dietary statements and the practical provision of lysine reduction therapies. Results from the questionnaire, statements from the PDE consensus guidelines, new data from the literature, as well as clinical practice experience of the metabolic dietitian group form the basis of these updated practical diet recommendations. These dietary management recommendations can support dietitians, nutritionists, and physicians in initiation and monitoring of lysine reduction therapies for PDE-ALDH7A1 patients and families.

Tolerable Upper Intake Level for Individual Amino Acids in Humans: A Narrative Review of Recent Clinical Studies

Individual amino acids are widely popular as supplements because of various perceived and real health benefits. However, currently, there are no recommendations set by national health agencies for tolerable upper intake levels (UL) for amino acids because of a lack of well-conducted human dose-response trials. In the past decade, under the initiative of the International Council on Amino Acid Science, a nonprofit organization, a series of UL human clinical studies were conducted. The goal of this narrative review is to summarize the studies on 6 essential amino acids (leucine, tryptophan, methionine, lysine, histidine, and phenylalanine), 2 nonessential amino acids (arginine and serine), and 2 nonproteinogenic amino acids (ornithine and citrulline) and provide the first set of ULs. A brief background of the concept of the DRI framework of UL, the concept of UL for amino acids, and a perspective of the results are also provided. The data suggest that in relatively healthy adult individuals, the tested amino acids are well tolerated, and ULs, or the no-observed-adverse-effect-level (NOAEL), lowest-observed-adverse-effect-level (LOAEL), can be determined. The ULs were for leucine-young (35 g/d), tryptophan (4.5 g/d), and leucine-elderly (30 g/d); NOAEL and LOAEL for methionine at 3.2 and 6.4 g/d, respectively; NOAEL for arginine (30 g/d); NOAEL and LOAEL for lysine at 6 and 7.5 g/d, respectively; NOAEL and LOAEL for histidine at 8 and 12 g/d, respectively; and NOAEL for phenylalanine (12 g/d), serine (12 g/d), ornithine (12 g/d) and citrulline (24 g/d). This first set of human UL data are hoped to help national and international agencies set safety standards for supplemental amino acids.

Association Between Lysine Reduction Therapies and Cognitive Outcomes in Patients With Pyridoxine-Dependent Epilepsy

BACKGROUND AND OBJECTIVES

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is a developmental epileptic encephalopathy characterized by seizure improvement after pyridoxine supplementation. Adjunct lysine reduction therapies (LRTs) reduce the accumulation of putative neurotoxic metabolites with the goal to improve developmental outcomes. Our objective was to examine the association between treatment with LRTs and cognitive outcomes.

METHODS

Participants were recruited from within the International Registry for Patients with Pyridoxine-Dependent Epilepsy from August 2014 through March 2021. The primary outcome was standardized developmental test scores associated with overall cognitive ability. The relationship between test scores and treatment was analyzed with multivariable linear regression using a mixed-effects model. A priori, we hypothesized that treatment in early infancy with pyridoxine and LRTs would result in a normal developmental outcome. A subanalysis was performed to evaluate the association between cognitive outcome and LRTs initiated in the first 6 months of life.

RESULTS

A total of 112 test scores from 60 participants were available. On average, treatment with pyridoxine and LRTs was associated with a nonsignificant increase of 6.9 points (95% CI -2.7 to 16.5) on developmental testing compared with treatment with pyridoxine alone. For the subanalysis, a total of 14 developmental testing scores were available from 8 participants. On average, treatment with pyridoxine and LRTs in the first 6 months of life was associated with a significant increase of 21.9 points (95% CI 1.7-42.0) on developmental testing.

DISCUSSION

Pyridoxine and LRTs at any age was associated with mild improvement in developmental testing, and treatment in early infancy was associated with a clinically significant increase in developmental test scores. These results provide insight into the mechanism of intellectual and developmental disability in PDE-ALDH7A1 and emphasize the importance of treatment in early infancy with both pyridoxine and LRTs.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that in PDE-ALDH7A1, pyridoxine and LRTs compared with pyridoxine alone is not significantly associated with overall higher developmental testing scores, but treatment in the first 6 months of life is associated with significantly higher developmental testing scores.

Recommendations for diagnosing and managing individuals with glutaric aciduria type 1: Third revision

Glutaric aciduria type 1 is a rare inherited neurometabolic disorder of lysine metabolism caused by pathogenic gene variations in GCDH (cytogenic location: 19p13.13), resulting in deficiency of mitochondrial glutaryl-CoA dehydrogenase (GCDH) and, consequently, accumulation of glutaric acid, 3-hydroxyglutaric acid, glutaconic acid and glutarylcarnitine detectable by gas chromatography/mass spectrometry (organic acids) and tandem mass spectrometry (acylcarnitines). Depending on residual GCDH activity, biochemical high and low excreting phenotypes have been defined. Most untreated individuals present with acute onset of striatal damage before age 3 (to 6) years, precipitated by infectious diseases, fever or surgery, resulting in irreversible, mostly dystonic movement disorder with limited life expectancy. In some patients, striatal damage develops insidiously. In recent years, the clinical phenotype has been extended by the finding of extrastriatal abnormalities and cognitive dysfunction, preferably in the high excreter group, as well as chronic kidney failure. Newborn screening is the prerequisite for pre-symptomatic start of metabolic treatment with low lysine diet, carnitine supplementation and intensified emergency treatment during catabolic episodes, which, in combination, have substantially improved neurologic outcome. In contrast, start of treatment after onset of symptoms cannot reverse existing motor dysfunction caused by striatal damage. Dietary treatment can be relaxed after the vulnerable period for striatal damage, that is, age 6 years. However, impact of dietary relaxation on long-term outcomes is still unclear. This third revision of evidence-based recommendations aims to re-evaluate previous recommendations (Boy et al., J Inherit Metab Dis, 2017;40(1):75-101; Kolker et al., J Inherit Metab Dis 2011;34(3):677-694; Kolker et al., J Inherit Metab Dis, 2007;30(1):5-22) and to implement new research findings on the evolving phenotypic diversity as well as the impact of non-interventional variables and treatment quality on clinical outcomes.

An Atypical Presentation of Pyridoxine-Dependent Epilepsy Diagnosed with Whole Exome Sequencing and Treated with Lysine Restriction and Supplementation with Arginine and Pyridoxine

Pyridoxine dependent-developmental and epileptic encephalopathy (PD-DEE) or pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder caused by biallelic pathogenic variants in ALDH7A1. It classically presents as intractable infantile-onset seizures unresponsive to multiple antiepileptic drugs (AEDs) but with a profound response to large doses of pyridoxine (B6). We report a case of PDE with an atypical clinical presentation. The patient presented at 3 days of life with multifocal seizures, fever, increased work of breathing, decreased left ventricular systolic function, and lactic acidosis, raising suspicion for a mitochondrial disorder or infectious process. Within 1.5 weeks of presentation, seizure activity resolved with antiepileptic therapy. Whole exome sequencing (WES) revealed homozygous pathogenic variants in ALDH7A1 (c.1279G > C, p.E427Q) and confirmed the diagnosis of PDE. Follow-up biochemical testing demonstrated elevated urine pipecolic acid. In the second week of life, the patient was initiated on triple therapy, including pyridoxine supplementation, low lysine diet, and arginine supplementation, which he tolerated well. Urine pipecolic acid levels responded accordingly after initiation of therapy. Our case illustrates the diagnostic challenges in PDE, the utility of rapid WES in such cases, and the response in urine pipecolic acid to therapy.

L-lysine: its antagonism with L-arginine in controlling viral infection. Narrative Literature Review

Knowledge about viral characteristics, mechanisms of entry into the host cell and multiplication/dissemination can help in the control and treatment of viral pathologies. Several nutritional factors linked to the host may favor viral multiplication and their control, may lead to new prophylactic alternatives and/or antiviral therapies. The objective of this review is to discuss the relationship between the amino acid L-lysine and the control of viral infections, aiming at a possible therapeutic property. This research used databases such as PubMed, Web of Science, Scielo, Medline and Google Scholar, as well as searching for references cited by journals. The time frame covered the period between 1964 and January 2022. The observed studies have shown that the usual antiviral therapies are not able to interfere with the viruses in their latent state, however, they can interfere with the adhesion and fusion of viral particles or the production of proteins, which play an important role in viral epidemiology and control, particularly in the initial moment and in the reactivation. Lysine is an amino acid that can interfere mainly in the formation of capsid proteins and DNA by a competitive antagonism with amino acid arginine, which is an essential amino acid for some viruses and also by promoting the increase of arginase, increasing the catabolism of arginine. Although there is evidence of the importance of L-lysine in viral control, more studies are needed, with a view to new antiviral therapies.

Glutaric Acidemia, Pathogenesis and Nutritional Therapy

Glutaric acidemia (GA) are heterogeneous, genetic diseases that present with specific catabolic deficiencies of amino acid or fatty acid metabolism. The disorders can be divided into type I and type II by the occurrence of different types of recessive mutations of autosomal, metabolically important genes. Patients of glutaric acidemia type I (GA-I) if not diagnosed very early in infanthood, experience irreversible neurological injury during an encephalopathic crisis in childhood. If diagnosed early the disorder can be treated successfully with a combined metabolic treatment course that includes early catabolic emergency treatment and long-term maintenance nutrition therapy. Glutaric acidemia type II (GA- II) patients can present clinically with hepatomegaly, non-ketotic hypoglycemia, metabolic acidosis, hypotonia, and in neonatal onset cardiomyopathy. Furthermore, it features adult-onset muscle-related symptoms, including weakness, fatigue, and myalgia. An early diagnosis is crucial, as both types can be managed by simple nutraceutical supplementation. This review discusses the pathogenesis of GA and its nutritional management practices, and aims to promote understanding and management of GA. We will provide a detailed summary of current clinical management strategies of the glutaric academia disorders and highlight issues of nutrition therapy principles in emergency settings and outline some specific cases.

Clinical and biochemical outcome of a patient with pyridoxine-dependent epilepsy treated by triple therapy (pyridoxine supplementation, lysine-restricted diet, and arginine supplementation)

Pyridoxine-dependent epilepsy (PDE) is a recessive genetic disease characterized by epileptic encephalopathy with therapeutic response to pharmacological doses of pyridoxine and resistance to anti-epileptic treatments. The recent discovery in 2006 of the genetic defect antiquitin (ALDH7A1, OMIM #266100) has helped to understand the underlying mechanism, which is the accumulation of neurotoxic intermediates in the lysine catabolic pathway. The goal of the new therapeutic approach, termed triple therapy (TT) (pyridoxine, lysine-restricted diet and arginine supplementation), is to improve epilepsy control and neurocognitive development in patients with PDE. We present the 3-year treatment outcome for a child with PDE on pyridoxine treatment (started at age 5 months), lysine-restricted diet (started at age 17 months) and arginine supplementation therapy (started at age 19 months). The TT was well-tolerated with good compliance. No adverse events were reported. We observed a neurodevelopmental improvement, significantly fewer seizures, and a reduction of pipecolic acid (PA) as a biomarker of the illness. Our results show an improving clinical evolution, supporting and extending previous studies reporting efficacy of TT.

Dietary management and growth outcomes in children with propionic acidemia: A natural history study

BACKGROUND

Propionic acidemia (PROP) is an autosomal recessive inherited deficiency of propionyl-CoA carboxylase (PCC) which is involved in the catalytic breakdown of the amino acids valine, isoleucine, methionine, and threonine. PROP nutritional management is based on dietary protein restriction and use of special medical formulas which are free of the offending amino acids, but are enriched in leucine. The resulting imbalance among branched-chain amino acids negatively impacts plasma concentrations of valine and isoleucine, which might impact growth in children with PROP.

OBJECTIVE AND METHODS

Our primary objective was to describe dietary protein and calorie intake and their impact on long-term growth outcomes of four PROP patients. This was accomplished through a longitudinal retrospective chart review following the cohort from birth to 18 years.

RESULTS

All children (n = 4) had poor growth outcomes with persistently reduced height-for-age Z scores, and elevated weight and body mass index (BMI) Z scores. Energy intakes for all subjects were within 80% to 120% of the dietary reference intakes for age. All children had low intakes of intact protein compared with current guidelines and were supplemented with medical formula and single l-amino acids (valine and/or isoleucine), which led to the excess consumption of total protein.

CONCLUSION

Despite adequate total protein and energy intakes, all children had persistently low height Z scores. Restricted intact protein consumption together with the abundant use of medical formula could have affected overall growth. To optimize dietary management in patients with PROP, further research is needed to determine the optimal intake of medical formula relative to intact protein.

Consensus guidelines for the diagnosis and management of pyridoxine-dependent epilepsy due to α-aminoadipic semialdehyde dehydrogenase deficiency

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is an autosomal recessive condition due to a deficiency of α-aminoadipic semialdehyde dehydrogenase, which is a key enzyme in lysine oxidation. PDE-ALDH7A1 is a developmental and epileptic encephalopathy that was historically and empirically treated with pharmacologic doses of pyridoxine. Despite adequate seizure control, most patients with PDE-ALDH7A1 were reported to have developmental delay and intellectual disability. To improve outcome, a lysine-restricted diet and competitive inhibition of lysine transport through the use of pharmacologic doses of arginine have been recommended as an adjunct therapy. These lysine-reduction therapies have resulted in improved biochemical parameters and cognitive development in many but not all patients. The goal of these consensus guidelines is to re-evaluate and update the two previously published recommendations for diagnosis, treatment, and follow-up of patients with PDE-ALDH7A1. Members of the International PDE Consortium initiated evidence and consensus-based process to review previous recommendations, new research findings, and relevant clinical aspects of PDE-ALDH7A1. The guideline development group included pediatric neurologists, biochemical geneticists, clinical geneticists, laboratory scientists, and metabolic dieticians representing 29 institutions from 16 countries. Consensus guidelines for the diagnosis and management of patients with PDE-ALDH7A1 are provided.

Beneficial outcome of early dietary lysine restriction as an adjunct to pyridoxine therapy in a child with pyridoxine dependant epilepsy due to Antiquitin deficiency

Pyridoxine-dependent epilepsy (PDE) is a potentially treatable vitamin-responsive epileptic encephalopathy. The most prevalent form of PDE is due to an underlying genetic defect in ALDH7A1 encoding Antiquitin (ATQ), an enzyme with α-aminoadipic semialdehyde dehydrogenase (AASADH) activity which facilitates cerebral lysine degradation. Devastating outcomes including intellectual disability and significant developmental delays are still observed in 75% to 80% of pyridoxine responsive individuals with good seizure control, potentially attributable to the accumulation of toxic intermediates α-aminoadipic semialdehyde (AASA) and its cyclic form Δ1-piperideine-6-carboxylate (P6C) in plasma, urine and CSF. Thus, adjunct treatment strategies incorporating lysine restriction and arginine supplementation, separately or in combination with pyridoxine have been attempted to enhance seizure control and improve cognitive function. We describe a 4 year old girl with classical PDE who demonstrated significant improvements in clinical, neurological and developmental outcomes including absence of clinical seizures and cessation of antiepileptic medications since age 3 months, normalisation of EEG, significant improvement in the white matter signal throughout the cerebrum on neuroimaging and significant reduction in urine P6C and pipecolic acid levels post- combined therapy with lysine restricted diet in conjunction with pyridoxine and folinic acid. Lysine restriction was well tolerated with impressive compliance and plasma lysine levels remained within the lower reference ranges; mean level 70 μmol/L (ref range 52-196 μmol/L). This case further emphasizes the benefit of early dietary intervention as an effective adjunct in the management of PDE.