Screening of Organic Acidurias by Gas Chromatography-Mass Spectrometry (GC-MS)

Organic acidurias or acidemias are a group of diverse disorders caused by decreased or diminished activity of specific enzyme or transporter involved in the metabolism of amino acids, carbohydrates, fatty acids, and nucleic acids. Organic acidurias are generally inherited but may be acquired due to deficiency of certain cofactors or vitamins. As clinical symptoms are of nonspecific nature, definitive diagnosis of organic aciduria requires measurement of organic acids in urine or blood and sometimes enzyme activity in the cells. Gas chromatography-mass spectrometry (GC-MS) is a commonly used method for screening of organic acidurias.GC-MS procedure described here involves the use of urine volume that contains 1 μmole (113 μg) of creatinine. Internal standards (tropic and 2-ketocaproic acids) are added to the samples, followed by treatment with hydroxylamine to form oxime derivatives of the ketoacids. The mixture is then acidified, and organic acids are extracted in ethyl acetate. The organic extract is concentrated to dryness, and the residue is treated with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)/trimethylchlorosilane (TMCS)/pyridine to form the trimethylsilyl (TMS) derivatives of the organic acids. The derivatized extract is then directly injected onto GC-MS for analysis.

Tandem Mass Spectrometry for the Analysis of Plasma/Serum Acylcarnitines for the Diagnosis of Certain Organic Acidurias and Fatty Acid Oxidation Disorders

Acylcarnitines are formed in the mitochondria by esterification between carnitine and acyl-CoAs. This occurs enzymatically via carnitine acyltransferases. Specific acylcarnitines accumulate as a result of various organic acidurias and fatty acid oxidation disorders, and, thus, acylcarnitines profiles are used for the diagnosis of these disorders. Acylcarnitines monitoring can also be used for the follow-up of patients with these disorders. Tandem mass spectrometry (MS/MS) is the most commonly used method for the analysis of acylcarnitines. An MS/MS method for the quantification of a number of acylcarnitines is described. The method involves butylation of acylcarnitines using acidified butanol. Butylated acylcarnitines are analyzed using flow injection and precursor ion scan. Multiple-reaction monitoring (MRM) is used for the analysis of low-molecular-weight acylcarnitines.

A knock-in rat model unravels acute and chronic renal toxicity in glutaric aciduria type I

Glutaric aciduria type I (GA-I, OMIM # 231670) is an autosomal recessive inborn error of metabolism caused by deficiency of the mitochondrial enzyme glutaryl-CoA dehydrogenase (GCDH). The principal clinical manifestation in GA-I patients is striatal injury most often triggered by catabolic stress. Early diagnosis by newborn screening programs improved survival and reduced striatal damage in GA-I patients. However, the clinical phenotype is still evolving in the aging patient population. Evaluation of long-term outcome in GA-I patients recently identified glomerular filtration rate (GFR) decline with increasing age. We recently created the first knock-in rat model for GA-I harboring the mutation p.R411W (c.1231 C>T), corresponding to the most frequent GCDH human mutation p.R402W. In this study, we evaluated the effect of an acute metabolic stress in form of high lysine diet (HLD) on young Gcdh^ki/ki rats. We further studied the chronic effect of GCDH deficiency on kidney function in a longitudinal study on a cohort of Gcdh^ki/ki rats by repetitive ⁶⁸Ga-EDTA positron emission tomography (PET) renography, biochemical and histological analyses. In young Gcdh^ki/ki rats exposed to HLD, we observed a GFR decline and biochemical signs of a tubulopathy. Histological analyses revealed lipophilic vacuoles, thinning of apical brush border membranes and increased numbers of mitochondria in proximal tubular (PT) cells. HLD also altered OXPHOS activities and proteome in kidneys of Gcdh^ki/ki rats. In the longitudinal cohort, we showed a progressive GFR decline in Gcdh^ki/ki rats starting at young adult age and a decline of renal clearance. Histopathological analyses in aged Gcdh^ki/ki rats revealed tubular dilatation, protein accumulation in PT cells and mononuclear infiltrations. These observations confirm that GA-I leads to acute and chronic renal damage. This raises questions on indication for follow-up on kidney function in GA-I patients and possible therapeutic interventions to avoid renal damage.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Long-term N-carbamylglutamate treatment of hyperammonemia in patients with classic organic acidemias

Background

Classic organic acidurias (OAs) usually characterized by recurrent episodes of acidemia, ketonuria, and hyperammonemia leading to coma and even death if left untreated. Acute hyperammonemia episodes can be treated effectively with N-carbamylglutamate (NCG). The effect of the long-term efficacy of N-carbamylglutamate is little known.

Material-Methods

This retrospective study was conducted at Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty, Pediatric Nutrition and Metabolism Clinic between January 2012 to January 2018. Patients with classic OAs were enrolled in the study. Patients' ammonia levels, hospitalization needs, hyperammonemia episodes, and management of hyperammonemia were recorded. NCG usage for more than consecutively 15 days was considered as a long-term treatment.

Results

Twenty-one patients, consisting of eleven patients with methylmalonic acidemia (MMA) and ten patients with propionic acidemia (PA) were eligible for the study. N-carbamylglutamate was used as ammonia scavenger for a total of 484 months with a median period of 23 months (min-max: 3-51 months) in all patients. A significant decrease in plasma ammonia levels was detected during long term NCG treatment (55.31 ± 13.762 μmol/L) in comparison with pre NCG treatment period (69.64 ± 17.828 μmol/L) (p = 0.021). Hospitalization required hyperammonemia episodes decreased with NCG treatment (p = 0.013). In addition, hyperammonemia episodes were also successfully treated with NCG (p = 0.000). Mean initial and final ammonia levels at the time of hyperammonemia episodes were 142 ± 46.495 μmol/L and 42.739 ± 12.120 μmol/L, respectively. The average NCG dosage was 85 mg/kg/day (range 12.5-250 mg/kg/day). No apparent side effects were observed.

Conclusion

N-Carbamylglutamate may be deemed an effective and safe treatment modality in the chronic management of hyperammonemia in patients with PA and MMA.

[Results of the neonatal screening on Western Andalusia after a decade of experience.]

OBJECTIVE

The main justification of this study was to describe our experience in neonatal screening and to define the prevalence of the diseases included in the neonatal screening program in Andalusia, among which are congenital hypothyroidism, expanded screening (aminoacidopathies, mitochondrial beta-oxidation defects and organic acidurias), cystic fibrosis, and screening for sickle cell anemia.

METHODS

The study was carried out in the Metabolopathies Unit of the Virgen del Rocío Hospital in Seville with samples of newborns from Western Andalusia (Cádiz, Córdoba, Huelva and Seville) and autonomous city of Ceuta. A total of 435,141 newborns were studied (from the period from April 1st 2009 to December 31st 2019) to rule out congenital hypothyroidism and expanded screening; 378,306 for cystic fibrosis from May 1st 2011 to the same date described above. Finally, sickle cell anemia screening was included, which comprised a total of 55,576 newborns from November 26th, 2018 to the same period as the previous ones. Statistical analysis was performed using IBM SPSS software (version 22, SPSS INC., USA).

RESULTS

The study revealed a prevalence of 1:1565 newborns for congenital hypothyroidism, 1:1532 newborns for extended screening, 1:6.878 newborns for cystic fibrosis, and a 1:11.115 newborns for sickle cell disease.

CONCLUSIONS

The neonatal screening program allows a large number of newborns to benefit from the early detection of certain serious congenital diseases. This aim improves the morbidity and mortality of those who suffer from them.

Disruption of mitochondrial functions and oxidative stress contribute to neurologic dysfunction in organic acidurias

Organic acidurias (OADs) are inherited disorders of amino acid metabolism biochemically characterized by accumulation of short-chain carboxylic acids in tissues and biological fluids of the affected patients and clinically by predominant neurological manifestations. Some of these disorders are amenable to treatment, which significantly decreases mortality and morbidity, but it is still ineffective to prevent long-term neurologic and systemic complications. Although pathogenesis of OADs is still poorly established, recent human and animal data, such as lactic acidosis, mitochondrial morphological alterations, decreased activities of respiratory chain complexes and altered parameters of oxidative stress, found in tissues from patients and from genetic mice models with these diseases indicate that disruption of critical mitochondrial functions and oxidative stress play an important role in their pathophysiology. Furthermore, organic acids that accumulate in the most prevalent OADs were shown to compromise bioenergetics, by decreasing ATP synthesis, mitochondrial membrane potential, reducing equivalent content and calcium retention capacity, besides inducing mitochondrial swelling, reactive oxygen and nitrogen species generation and apoptosis. It is therefore presumed that secondary mitochondrial dysfunction and oxidative stress caused by major metabolites accumulating in OADs contribute to tissue damage in these pathologies.

Prevention by L-carnitine of DNA damage induced by 3-hydroxy-3-methylglutaric and 3-methylglutaric acids and experimental evidence of lipid and DNA damage in patients with 3-hydroxy-3-methylglutaric aciduria

3-hydroxy-3-methylglutaric aciduria (HMGA) is an inherited disorder of the leucine catabolic pathway in which occurs a deficiency of the 3-hydroxy-3-methylglutaryl-CoA lyase enzyme. Therefore, the organic acids 3-hydroxy-3-methylglutaric (HMG) and 3-methylglutaric (MGA), mainly, accumulate in tissues of affected patients. Lately, much attention has been focused on free radicals as mediators of tissue damage in human diseases, causing lipid peroxidation, protein oxidation and DNA damage. The treatment of this disease is based in a restricted protein ingest and supplementation with l-carnitine (LC), an antioxidant and detoxifying agent. In the present work, we investigated the in vitro oxidative damage to DNA induced by the accumulation of organic acids and oxidative stress parameters in vivo of patients with 3-HMG, as well as the effect of the recommended therapy. The in vitro DNA damage was analyzed by the alkaline comet assay in leukocytes incubated with HMG and MGA (1 mM, 2.5 mM and 5 mM) and co-incubated with LC (90 μM and 150 μM). The in vivo urinary 15-F2t-isoprostane levels and urinary oxidized guanine species were measured by ELISA kits in patient's urine before and after the treatment with LC. HMG and MGA induced a DNA damage index (DI) significantly higher than that of the control group. The DI was significantly reduced in the presence of LC. It was also verified a significant increase of oxidized guanine species and urinary isoprostane levels, biomarker of oxidative DNA damage and lipid peroxidation respectively, in patients before treatment. After the treatment and supplementation with LC, patients presented significantly lower levels of those biomarkers. Analyzing the data together, we can conclude that HMGA patients present oxidative lipid and DNA damage, which is induced by HMG and MGA, and the antioxidant therapy with LC can prevent that kind of injuries.

Decreased plasma l-arginine levels in organic acidurias (MMA and PA) and decreased plasma branched-chain amino acid levels in urea cycle disorders as a potential cause of growth retardation: Options for treatment

BACKGROUND AND AIM

Patients with methylmalonic acidemia (MMA) and propionic acidemia (PA) and urea cycle disorders (UCD), treated with a protein restricted diet, are prone to growth failure. To obtain optimal growth and thereby efficacious protein incorporation, a diet containing the essential and functional amino acids for growth is necessary. Optimal growth will result in improved protein tolerance and possibly a decrease in the number of decompensations. It thus needs to be determined if amino acid deficiencies are associated with the growth retardation in these patient groups. We studied the correlations between plasma L-arginine levels, plasma branched chain amino acids (BCAA: L-isoleucine, L-leucine and L-valine) levels (amino acids known to influence growth), and height in MMA/PA and UCD patients.

METHODS

We analyzed data from longitudinal visits made in stable metabolic periods by patients registered at the European Registry and Network for Intoxication Type Metabolic Diseases (E-IMD, Chafea no. 2010 12 01).

RESULTS

In total, 263 MMA/PA and 311 UCD patients were included, all aged below 18 years of age. In patients with MMA and PA, height z-score was positively associated with patients' natural-protein-to-energy prescription ratio and their plasma L-valine and L-arginine levels, while negatively associated with the amount of synthetic protein prescription and their age at visit. In all UCDs combined, height z-score was positively associated with the natural-protein-to-energy prescription ratio. In those with carbamylphosphate synthetase 1 deficiency (CPS1-D), those with male ornithine transcarbamylase deficiency (OTC-D), and those in the hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome subgroup, height z-score was positively associated with patients' plasma L-leucine levels. In those with argininosuccinate synthetase deficiency (ASS-D) and argininosuccinate lyase deficiency (ASL-D), height was positively associated with patients' plasma L-valine levels.

CONCLUSION

Plasma L-arginine and L-valine levels in MMA/PA patients and plasma L-leucine and L-valine levels in UCD patients, as well as the protein-to-energy prescription ratio in both groups were positively associated with height. Optimization of these plasma amino acid levels is essential to support normal growth and increase protein tolerance in these disorders. Consequently this could improve the protein-to-energy intake ratio.

Organic acidurias in adults: late complications and management

Organic acidurias (synonym, organic acid disorders, OADs) are a heterogenous group of inherited metabolic diseases delineated with the implementation of gas chromatography/mass spectrometry in metabolic laboratories starting in the 1960s and 1970s. Biochemically, OADs are characterized by accumulation of mono-, di- and/or tricarboxylic acids ("organic acids") and corresponding coenzyme A, carnitine and/or glycine esters, some of which are considered toxic at high concentrations. Clinically, disease onset is variable, however, affected individuals may already present during the newborn period with life-threatening acute metabolic crises and acute multi-organ failure. Tandem mass spectrometry-based newborn screening programmes, in particular for isovaleric aciduria and glutaric aciduria type 1, have significantly reduced diagnostic delay. Dietary treatment with low protein intake or reduced intake of the precursor amino acid(s), carnitine supplementation, cofactor treatment (in responsive patients) and nonadsorbable antibiotics is commonly used for maintenance treatment. Emergency treatment options with high carbohydrate/glucose intake, pharmacological and extracorporeal detoxification of accumulating toxic metabolites for intensified therapy during threatening episodes exist. Diagnostic and therapeutic measures have improved survival and overall outcome in individuals with OADs. However, it has become increasingly evident that the manifestation of late disease complications cannot be reliably predicted and prevented. Conventional metabolic treatment often fails to prevent irreversible organ dysfunction with increasing age, even if patients are considered to be "metabolically stable". This has challenged our understanding of OADs and has elicited the discussion on optimized therapy, including (early) organ transplantation, and long-term care.

Development and Psychometric Evaluation of the MetabQoL 1.0: A Quality of Life Questionnaire for Paediatric Patients with Intoxication-Type Inborn Errors of Metabolism

INTRODUCTION

This study is part of the "European network and registry for intoxication type metabolic diseases" (E-IMD) project. Intoxication-type inborn errors of metabolism (IT-IEM) such as urea cycle disorders (UCD) and organic acidurias (OA) have a major impact on patients' lives. Patients have to adhere to strict diet and medication and may suffer from metabolic crises and neurocognitive impairment. Disease-specific health-related quality of life (HrQoL) assessment questionnaires are the method of choice to estimate the subjective burden of a disease. To date, no such instrument is available for IT-IEM.

METHODS

Disease-specific patient- and parent-reported HrQoL questions were constructed in German based on focus group interviews with patients and parents. Questionnaires for patients from 8 to 18 years were piloted with 14 participants (n = 9 children and adolescents, n = 5 parents) by cognitive debriefing and tested psychometrically with 80 participants (n = 38 patients, n = 42 parents) for item characteristics, validity, and reliability to construct the first version of a disease-specific HrQoL questionnaire.

RESULTS

Twenty-eight questions were selected based on item descriptives. Scales of self- and proxy questionnaires demonstrated acceptable to excellent reliability in terms of internal consistency (Cronbach's α = 0.70-0.93). Scales and total scores correlated with those of generic HrQoL questionnaires, showing convergent validity.

DISCUSSION

The MetabQoL 1.0 questionnaire exhibits sound psychometric properties and is a promising step towards assessing patient-reported outcomes in research and clinical practice. It provides a solid basis for translation into other languages and further elaboration and psychometric exploration in larger populations.

Clinical experience with N-carbamylglutamate in a single-centre cohort of patients with propionic and methylmalonic aciduria

Background

The effect of long-term N-carbamylglutamate (NCG) treatment on the rate and severity of decompensations due to propionic aciduria (PA) and methylmalonic aciduria (MMA) is unknown. This paper presents clinical experience from a single-centre cohort of patients with PA and MMA who received continuous long-term treatment with NCG.

Methods

The effect of oral NCG treatment (initial dose: 50 mg/kg/day) was investigated in patients with PA or MMA who were experiencing frequent progressive episodes of metabolic decompensation, who had pathological levels of ammonia, and who were referred to the Division of Metabolic Diseases, University Hospital of Padova between August 2014 and December 2015. Clinical and biochemical data, including the number of metabolic decompensations, lactic acid, uric acid and plasma ammonia levels, protein intake and body weight, were collected before and after the initiation of NCG treatment.

Results

Eight patients with PA (n = 4) and MMA (n = 4) aged 2–20 years were treated with NCG (50 mg/kg/day) for 7–16 months. Metabolic decompensation episodes decreased in number and severity, with three of the patients having no episodes (pre-treatment: 24 episodes; post-treatment: 9 episodes). After NCG treatment, all episodes were treated at home and none required hospitalisation, lactic acid values were 1.3–2.1 mmol/L and uric acid values were 0.21–0.36 mmol/L. Significant reductions in blood ammonia levels after NCG initiation were observed in five patients, whereas levels were reduced or maintained in the normal range in the remainder. Over the treatment period, patients had an increase in natural protein intake of 20–50% and gained 0–6.5 kg in bodyweight.

Conclusion

These observations suggest that, in addition to short-term benefits for the acute treatment of hyperammonaemia, NCG may be effective and well tolerated as a long-term treatment in patients with severe PA and MMA, and that further prospective studies are warranted.

Pilot Experience with an External Quality Assurance Scheme for Acylcarnitines in Plasma/Serum

The analysis of acylcarnitines (AC) in plasma/serum is established as a useful test for the biochemical diagnosis and the monitoring of treatment of organic acidurias and fatty acid oxidation defects. External quality assurance (EQA) for qualitative and quantitative AC is offered by ERNDIM and CDC in dried blood spots but not in plasma/serum samples. A pilot interlaboratory comparison between 14 European laboratories was performed over 3 years using serum/plasma samples from patients with an established diagnosis of an organic aciduria or fatty acid oxidation defect. Twenty-three different samples with a short clinical description were circulated. Participants were asked to specify the method used to analyze diagnostic AC, to give quantitative data for diagnostic AC with the corresponding reference values, possible diagnosis, and advice for further investigations.Although the reference and pathological concentrations of AC varied among laboratories, elevated marker AC for propionic acidemia, isovaleric acidemia, medium-chain acyl-CoA dehydrogenase, very long-chain acyl-CoA dehydrogenase, and multiple acyl-CoA dehydrogenase deficiencies were correctly identified by all participants allowing the diagnosis of these diseases. Conversely, the increased concentrations of dicarboxylic AC were not always identified, and therefore the correct diagnosis was not reach by some participants, as exemplified in cases of malonic aciduria and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. Misinterpretation occurred in those laboratories that used multiple-reaction monitoring acquisition mode, did not derivatize, or did not separate isomers. However, some of these laboratories suggested further analyses to clarify the diagnosis.This pilot experience highlights the importance of an EQA scheme for AC in plasma.

Quantification of Free Carnitine and Acylcarnitines in Plasma or Serum Using HPLC/MS/MS

Acylcarnitines are formed by esterification between fatty acids CoA or organic acids CoA molecules and carnitine. In various fatty acids oxidation defects and organic acidurias, there is increased concentration of corresponding acylcarnitines. Abnormalities in specific acylcarnitines are used in the diagnosis of fatty acids oxidation defects and organic acidurias. Most commonly used method for the assay of acylcarnitines is HPLC-tandem mass spectrometry (HPLC/MS/MS). A HPLC/MS/MS method is described for the quantification of number of acylcarnitines. The method involves butylation of carnitine/acylcarnitines using acidified butanol, HPLC flow injection, and measurement of acylcarnitines using precursor ion scan and multiple reactions monitoring (MRM).

Differences between acylcarnitine profiles in plasma and bloodspots

Quantification of acylcarnitines is used for screening and diagnosis of inborn error of metabolism (IEM). While newborn screening is performed in dried blood spots (DBSs), general metabolic investigation is often performed in plasma. Information on the correlation between plasma and DBS acylcarnitine profiles is scarce. In this study, we directly compared acylcarnitine concentrations measured in DBS with those in the corresponding plasma sample. Additionally, we tested whether ratios of acylcarnitines in both matrices are helpful for diagnostic purpose when primary markers fail.

STUDY DESIGN

DBS and plasma were obtained from controls and patients with a known IEM. (Acyl)carnitines were converted to their corresponding butyl esters and analyzed using HPLC/MS/MS.

RESULTS

Free carnitine concentrations were 36% higher in plasma compared to DBS. In contrast, in patients with carnitine palmitoyltransferase 1 (CPT-1) deficiency free carnitine concentration in DBS was 4 times the concentration measured in plasma. In carnitine palmitoyltransferase 2 (CPT-2) deficiency, primary diagnostic markers were abnormal in plasma but could also be normal in DBS. The calculated ratios for CPT-1 (C0/(C16+C18)) and CPT-2 ((C16+C18:1)/C2) revealed abnormal values in plasma. However, normal ratios were found in DBS of two (out of five) samples obtained from patients diagnosed with CPT-2.

CONCLUSIONS

Relying on primary acylcarnitine markers, CPT-1 deficiency can be missed when analysis is performed in plasma, whereas CPT-2 deficiency can be missed when analysis is performed in DBS. Ratios of the primary markers to other acylcarnitines restore diagnostic recognition completely for CPT-1 and CPT-2 in plasma, while CPT-2 can still be missed in DBS.

Organic acidurias: an updated review

Organic acidurias are an important class of inherited metabolic disorders arising due to defect in intermediary metabolic pathways of carbohydrate, amino acids and fatty acid oxidation. This review summarizes the current knowledge about the important organic acidurias in the Indian population. Specifically, diagnosis and principles of treatment of organic acidurias are covered. The salient features of common organic acidurias as well as their prevalence in various parts of the world are reviewed in some detail.