Guideline for the diagnosis and management of glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type I)

Diagnosis of glutaric aciduria type I based on neuroradiological findings: when neonatal screening fails

BACKGROUND

Glutaric aciduria type I (GA-I) is an autosomal recessive disorder affecting the metabolism of lysine, hydroxylysine, and tryptophan. Patients present in the first age of life with an irreversible motor disorder, and neuroradiological imaging can suggest the presence of the condition. Biochemically, the disorder is characterized by elevated levels of glutaric and 3-hydroxy glutaric acid in the urine and glutarylcarnitine in the blood. This latter metabolite can be detected in dried blood spots, and the condition can therefore be included in some newborn screening programs.

CASE PRESENTATION

We present the case of a patient affected by GA-I that was undetected by newborn screening in whom the diagnosis was clinically oriented at the age of nine months by acute neurological symptoms, represented by persistent tonic seizures, and by neuroimaging showing bilateral signal alterations in the basal ganglia. Biochemical data, including glutarylcarnitine in dried blood spots and urinary excretion of glutaric acid, were normal in the acute phase and during follow-up. Molecular analysis confirmed a diagnosis of GA-I, showing a homozygous M405V variant of the GCDH gene, which is common in African populations and associated with a low-excretor phenotype characteristic of the disorder.

CONCLUSIONS

In conclusion, although GA-I is included in neonatal screening programs, the biochemical markers in dried blood spots can be absent. Therefore, in patients of African origin, clinicians should maintain a high degree of vigilance in the presence of suggestive clinical and neuroradiological findings, even if biochemical parameters are normal.

Digital-Tier Strategy Improves Newborn Screening for Glutaric Aciduria Type 1

Glutaric aciduria type 1 (GA1) is a rare inherited metabolic disease increasingly included in newborn screening (NBS) programs worldwide. Because of the broad biochemical spectrum of individuals with GA1 and the lack of reliable second-tier strategies, NBS for GA1 is still confronted with a high rate of false positives. In this study, we aim to increase the specificity of NBS for GA1 and, hence, to reduce the rate of false positives through machine learning methods. Therefore, we studied NBS profiles from 1,025,953 newborns screened between 2014 and 2023 at the Heidelberg NBS Laboratory, Germany. We identified a significant sex difference, resulting in twice as many false-positives male than female newborns. Moreover, the proposed digital-tier strategy based on logistic regression analysis, ridge regression, and support vector machine reduced the false-positive rate by over 90% compared to regular NBS while identifying all confirmed individuals with GA1 correctly. An in-depth analysis of the profiles revealed that in particular false-positive results with high associated follow-up costs could be reduced significantly. In conclusion, understanding the origin of false-positive NBS and implementing a digital-tier strategy to enhance the specificity of GA1 testing may significantly reduce the burden on newborns and their families from false-positive NBS results.

Systemic delivery of AAV-GCDH ameliorates HLD-induced phenotype in a glutaric aciduria type I mouse model

Glutaric aciduria type 1 (GA1) is a rare inherited metabolic disorder caused by a deficiency of glutaryl-coenzyme A dehydrogenase (GCDH), with accumulation of neurotoxic metabolites, resulting in a complex movement disorder, irreversible brain damage, and premature death in untreated individuals. While early diagnosis and a lysine restricted diet can extend survival, they do not prevent neurological damage in approximately one-third of treated patients, and more effective therapies are required. Here we report the efficacy of adeno-associated virus 9 (AAV9)-mediated systemic delivery of human GCDH at preventing a high lysine diet (HLD)-induced phenotype in Gcdh -/- mice. Neonatal treatment with AAV-GCDH restores GCDH expression and enzyme activity in liver and striatum. This treatment protects the mice from HLD-aggressive phenotype with all mice surviving this exposure; in stark contrast, a lack of treatment on an HLD triggers very high accumulation of glutaric acid, 3-hydroxyglutaric acid, and glutarylcarnitine in tissues, with about 60% death due to brain accumulation of toxic lysine metabolites. AAV-GCDH significantly ameliorates the striatal neuropathology, minimizing neuronal dysfunction, gliosis, and alterations in myelination. Magnetic resonance imaging findings show protection against striatal injury. Altogether, these results provide preclinical evidence to support AAV-GCDH gene therapy for GA1.

Evaluation of the first 5 years of a glutaric aciduria type I neonatal screening programme in Asturias

INTRODUCTION

. Neonatal screening of glutaric aciduria type 1 (GA-1) has brought radical changes in the course and outcomes of this disease. This study analyses the outcomes of the first 5 years (2015-2019) of the AGA1 neonatal screening programme in our autonomous community.

MATERIAL

. We conducted an observational, descriptive and retrospective study. All neonates born between January 1, 2015 and December 31, 2019 that participated in the neonatal screening programme were included in the study. The glutarylcarnitine (C5DC) concentration in dry blood spot samples was measured by means of tandem mass spectrometry applying a cut-off point of 0.25 µmol/L.

RESULTS

. A total of 30 120 newborns underwent screening. We found differences in the C5DC concentration based on gestational age, type of feeding and hours of life at sample collection. These differences were not relevant for screening purposes. There were no differences between neonates with weights smaller and greater than 1500 g. Screening identified 2 affected patients and there were 3 false positives. There were no false negatives. The diagnosis was confirmed by genetic testing. Patients have been in treatment since diagnosis and have not developed encephalopathic crises in the first 4 years of life.

CONCLUSIONS

. Screening allowed early diagnosis of two cases of GA-1 in the first 5 years since its introduction in our autonomous community. Although there were differences in C5DC levels based on gestational age, type of feeding and hours of life at blood extraction, they were not relevant for screening.

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.

[Evaluation and optimization of newborn screening by structured long-term follow-up-using the example of inherited metabolic diseases]

Newborn screening (NBS) is a highly successful secondary prevention program with the goal of preventing severe sequelae of congenital, mostly genetic, diseases by identifying them as early as possible, ideally in the pre-symptomatic period. Studies to date have shown the important achievements of NBS programs but also reveal a number of relevant weaknesses. These include the often incompletely understood natural history and phenotypic diversity of rare diseases as well as the inadequate ability to accurately predict individual disease severity at an early stage and thus the uncertainties in case definition, risk stratification, and treatment indication.In light of the rapid developments in high-throughput genetic technologies and the associated opportunities for substantial future expansion of NBS programs, it seems overdue to make structured long-term follow-up and the subsequent evaluation of the long-term health benefits mandatory for individuals with rare diseases identified through NBS. This article explains the importance of long-term follow-up for the evaluation and continuous optimization of the screening. Long-term clinical outcomes of people with inherited metabolic diseases identified by NBS are presented as examples.

Neuroimaging findings of inborn errors of metabolism: urea cycle disorders, aminoacidopathies, and organic acidopathies

Although there are many types of inborn errors of metabolism (IEMs) affecting the central nervous system, also referred to as neurometabolic disorders, individual cases are rare, and their diagnosis is often challenging. However, early diagnosis is mandatory to initiate therapy and prevent permanent long-term neurological impairment or death. The clinical course of IEMs is very diverse, with some diseases progressing to acute encephalopathy following infection or fasting while others lead to subacute or slowly progressive encephalopathy. The diagnosis of IEMs relies on biochemical and genetic tests, but neuroimaging studies also provide important clues to the correct diagnosis and enable the conditions to be distinguished from other, more common causes of encephalopathy, such as hypoxia-ischemia. Proton magnetic resonance spectroscopy (¹H-MRS) is a powerful, non-invasive method of assessing neurological abnormalities at the microscopic level and can measure in vivo brain metabolites. The present review discusses neuroimaging findings, including those of ¹H-MRS, of IEMs focusing on intoxication disorders such as urea cycle disorders, aminoacidopathies, and organic acidopathies, which can result in acute life-threatening metabolic decompensation or crisis.

How guideline development has informed clinical research for organic acidurias (et vice versa)

Organic acidurias, such as glutaric aciduria type 1 (GA1), methylmalonic (MMA), and propionic aciduria (PA) are a prominent group of inherited metabolic diseases involving accumulation of eponymous metabolites causing endogenous intoxication. For all three conditions, guidelines for diagnosis and management have been developed and revised over the last years, resulting in three revisions for GA1 and one revision for MMA/PA. The process of clinical guideline development in rare metabolic disorders is challenged by the scarcity and limited quality of evidence available. The body of literature is often fragmentary and where information is present, it is usually derived from small sample sizes. Therefore, the development of guidelines for GA1 and MMA/PA was initially confronted with a poor evidence foundation that hindered formulation of concrete recommendations in certain contexts, triggering specific research projects and initiation of longitudinal, prospective observational studies using patient registries. Reversely, these observational studies contributed to evaluate the value of newborn screening, phenotypic diversities, and treatment effects, thus significantly improving the quality of evidence and directly influencing formulation and evidence levels of guideline recommendations. Here, we present insights into interactions between guideline development and (pre)clinical research for GA1 and MMA/PA, and demonstrate how guidelines gradually improved from revision to revision. We describe how clinical studies help to unravel the relative impact of therapeutic interventions on outcome and conclude that despite new and better quality of research data over the last decades, significant shortcomings of evidence regarding prognosis and treatment remain. It appears that development of clinical guidelines can directly help to guide research, and vice versa.

Does glutaric aciduria type 1 affect hearing function?

This study aimed to evaluate audiological findings among patients with glutaric aciduria type 1 (GA-1). We used a large test battery for the audiological evaluation of 17 individuals with GA-1 (the study group) and 20 healthy individuals (the control group). Conventional audiometry (0.125-8 kHz), distortion product otoacoustic emissions (DPOAEs) (1, 1.5, 2, 3, 4, 6, and 8 kHz), contralateral suppression of otoacoustic emissions, and auditory brainstem response (ABR) ( 30, 50, 70 and 90 dB nHL) were measured for all participants (n = 37). Mild sensorineural hearing loss was found in 77.47% (n = 13) of the patients with GA-1, and normal hearing thresholds were seen in 23.53% (n = 4). There were three asymptomatic patients at the time of diagnosis [two developed mild mental motor retardation (MMR) and one developed severe MMR during the follow-up], one with a normal hearing threshold and two with mild hearing loss), and 14 symptomatic patients (three with normal hearing thresholds and 11 with mild hearing loss). Seven of the symptomatic patients diagnosed following an encephalopathic crisis required intensive care and showed significantly worse hearing thresholds than those without symptoms [20.86 ± 4.47 vs. 15.44 ± 3.96 decibel hearing level (dB HL), p = 0.039*], while five had mild-to-moderate hearing loss. Acute encephalopathic crisis had a negative effect on hearing function in the symptomatic patients. The emission and contralateral suppression amplitude values of the study group were significantly lower compared to the control group (p < 0.05). The I-V interpeak latency and absolute latencies of ABR waves I, III, and V of the study group were observed to be significantly prolonged and morphologically distorted compared to those of the control group (p < 0.05). Five patients had MMR, and three had moderate MMR; all eight had mild-to-moderate hearing loss. In addition, of the eight patients with mild MMR, four had mild hearing loss. In particular, the morphological findings of ABR waves were significantly worse in the patients with severe and moderate MMR (p < 0.05). There was a significant correlation between a macrocephaly history (12 patients) and hearing loss (p = 0.041*). Magnetic resonance imaging findings were evaluated in all the 17 patients with GA-1, and typical fronto-temporal atrophy and sylvian fissure enlargement were observed. Our findings support that GA-1 is associated with auditory impairment, primarily in symptomatic patients. Adequate audiological test battery evaluation is essential in this context, particularly for symptomatic patients with a history of encephalopathic crises.

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.

Rare Disease Registries Are Key to Evidence-Based Personalized Medicine: Highlighting the European Experience

Rare diseases, such as inherited metabolic diseases, have been identified as a health priority within the European Union more than 20 years ago and have become an integral part of EU health programs and European Reference Networks. Having the potential to pool data, to achieve sufficient sample size, to overcome the knowledge gap on rare diseases and to foster epidemiological and clinical research, patient registries are recognized as key instruments to evidence-based medicine for individuals with rare diseases. Patient registries can be used for multiple purposes, such as (1) describing the natural history and phenotypic diversity of rare diseases, (2) improving case definition and indication to treat, (3) identifying strategies for risk stratification and early prediction of disease severity (4), evaluating the impact of preventive, diagnostic, and therapeutic strategies on individual health, health economics, and the society, and (5) informing guideline development and policy makers. In contrast to clinical trials, patient registries aim to gather real-world evidence and to achieve generalizable results based on patient cohorts with a broad phenotypic spectrum. In order to develop a consistent and sustained framework for rare disease registries, uniform core principles have been formulated and have been formalized through the European Rare Disease Registration Infrastructure. Adherence to these core principles and compliance with the European general data protection regulations ensures that data collected and stored in patient registries can be exchanged and pooled in a protected environment. To illustrate the benefits and limitations of patient registries on rare disease research this review focuses on inherited metabolic diseases.

Subdural hematoma in glutaric aciduria type 1: High excreters are prone to incidental SDH despite newborn screening

Subdural hematoma (SDH) was initially reported in 20% to 30% of patients with glutaric aciduria type 1 (GA1). A recent retrospective study found SDH in 4% of patients, but not in patients identified by newborn screening (NBS). 168 MRIs of 69 patients with GA1 (age at MRI 9 days - 73.8 years, median 3.2 years) were systematically reviewed for presence of SDH, additional MR and clinical findings in order to investigate the frequency of SDH and potential risk factors. SDH was observed in eight high-excreting patients imaged between 5.8 and 24.4 months, namely space-occupying SDH in two patients after minor accidental trauma and SDH as an incidental finding in six patients without trauma. In patients without trauma imaged at 3 to 30 months (n = 36, 25 NBS, 27/9 high/low excreters), incidence of SDH was 16.7% (16% in NBS). SDH was more common after acute (33.3%) than insidious onset of dystonia (14.3%) or in asymptomatic patients (5.9%). It was only seen in patients with wide frontoparietal CSF spaces and frontotemporal hypoplasia. High excreters were over-represented among patients with SDH (6/27 vs 0/9 low excreters), acute onset (10/12), and wide frontoparietal CSF spaces (16/19). Incidental SDH occurs despite NBS and early treatment in approximately one in six patients with GA1 imaged during late infancy and early childhood. Greater risk of high excreters is morphologically associated with more frequent enlargement of external CSF spaces including frontotemporal hypoplasia, and may be furthered aggravated by more pronounced alterations of cerebral blood volume and venous pressure.

The outcome of 41 Late-Diagnosed Turkish GA-1 Patients: A Candidate for the Turkish NBS

BACKGROUND

Glutaric aciduria type 1(GA-1) is an inherited cerebral organic aciduria. Untreated patients with GA-1 have a risk of acute encephalopathic crises during the first 6 years of life. In so far as GA-1 desperately does not exist in Turkish newborn screening (NBS) program, most patients in our study were late-diagnosed.

METHOD

This study included 41 patients diagnosed with acylcarnitine profile, urinary organic acids, mutation analyses in the symptomatic period. We presented with clinical, neuroradiological, and molecular data of our 41 patients.

RESULTS

The mean age at diagnosis was 14.8 ± 13.9 (15 days to 72 months) and, high blood glutaconic acid, glutarylcarnitine and urinary glutaric acid (GA) levels in 41 patients were revealed. Seventeen different mutations in the glutaryl-CoA dehydrogenase gene were identified, five of which were novel. The patients, most of whom were late-diagnosed, had a poor neurological outcome. Treatment strategies made a little improvement in dystonia and the frequency of encephalopathic attacks.

CONCLUSION

All GA-1 patients in our study were severely affected since they were late-diagnosed, while others show that GA-1 is a treatable metabolic disorder if it is diagnosed with NBS. This study provides an essential perspective of the severe impact on GA-1 patients unless it is diagnosed with NBS. We immediately advocate GA-1 to be included in the Turkish NBS.

The biochemical subtype is a predictor for cognitive function in glutaric aciduria type 1: a national prospective follow-up study

The aim of the study was a systematic evaluation of cognitive development in individuals with glutaric aciduria type 1 (GA1), a rare neurometabolic disorder, identified by newborn screening in Germany. This national, prospective, observational, multi-centre study includes 107 individuals with confirmed GA1 identified by newborn screening between 1999 and 2020 in Germany. Clinical status, development, and IQ were assessed using standardized tests. Impact of interventional and non-interventional parameters on cognitive outcome was evaluated. The majority of tested individuals (n = 72) showed stable IQ values with age (n = 56 with IQ test; median test age 11 years) but a significantly lower performance (median [IQR] IQ 87 [78-98]) than in general population, particularly in individuals with a biochemical high excreter phenotype (84 [75-96]) compared to the low excreter group (98 [92-105]; p = 0.0164). For all patients, IQ results were homogenous on subscale levels. Sex, clinical motor phenotype and quality of metabolic treatment had no impact on cognitive functions. Long-term neurologic outcome in GA1 involves both motor and cognitive functions. The biochemical high excreter phenotype is the major risk factor for cognitive impairment while cognitive functions do not appear to be impacted by current therapy and striatal damage. These findings implicate the necessity of new treatment concepts.

A generic emergency protocol for patients with inborn errors of metabolism causing fasting intolerance: A retrospective, single-center study and the generation of www.emergencyprotocol.net

Patients with inborn errors of metabolism causing fasting intolerance can experience acute metabolic decompensations. Long-term data on outcomes using emergency letters are lacking. This is a retrospective, observational, single-center study of the use of emergency letters based on a generic emergency protocol in patients with hepatic glycogen storage diseases (GSD) or fatty acid oxidation disorders (FAOD). Data on hospital admissions, initial laboratory results, and serious adverse events were collected. Subsequently, the website www.emergencyprotocol.net was generated in the context of the CONNECT MetabERN eHealth project following multiple meetings, protocol revisions, and translations. Representing 470 emergency protocol years, 127 hospital admissions were documented in 54/128 (42%) patients who made use of emergency letters generated based on the generic emergency protocol. Hypoglycemia (here defined as glucose concentration < 3.9 mmol/L) was reported in only 15% of hospital admissions and was uncommon in patients with ketotic GSD and patients with FAOD aged >5 years. Convulsions, coma, or death was not documented. By providing basic information, emergency letters for individual patients with hepatic GSD or the main FAOD can be generated at www.emergencyprotocol.net, in nine different languages. Generic emergency protocols are safe and easy for home management by the caregivers and the first hour in-hospital management to prevent metabolic emergencies in patients with hepatic GSD and medium-chain Acyl CoA dehydrogenase deficiency. The website www.emergencyprotocol.net is designed to support families and healthcare providers to generate personalized emergency letters for patients with hepatic GSD and the main FAOD.

Evaluation of the Clinical, Biochemical, Neurological, and Genetic Presentations of Glutaric Aciduria Type 1 in Patients From China

Purpose

To characterize the phenotypic and genotypic variations associated with Glutaric aciduria type 1 (GA1) in Chinese patients.

Methods

We analyzed the clinical, neuroradiological, biochemical, and genetic information from 101 GA1 patients in mainland China.

Results

20 patients were diagnosed by newborn screening and the remaining 81 cases were identified following clinical intervention. Macrocephaly was the most common presentation, followed by movement disorders and seizures. A total of 59 patients were evaluated by brain MRI and 58 patients presented with abnormalities, with widening of the sylvian fissures being the most common symptom. The concentration of glutarylcarnitine in the blood, glutarylcarnitine/capryloylcarnitine ratio, and urine levels of glutaric acid were increased in GA1 patients and were shown to decrease following intervention. A total of 88 patient samples were available for genotyping and 74 variants within the GCDH gene, including 23 novel variants, were identified. The most common variant was c.1244-2A > C (18.4%) and there were no significant differences in the biochemical or clinical phenotypes described for patients with the four most common variants: c.1244-2A > C, c.1064G > A, c.533G > A, and c.1147C > T. Patients identified by newborn screening had better outcomes than clinical patients.

Conclusion

Our findings expand the spectrum of phenotypes and genotypes for GA1 in Chinese populations and suggest that an expanded newborn screening program using tandem mass spectrometry may facilitate the early diagnosis and treatment of this disease, improving clinical outcomes for patients in China.

Impact of interventional and non-interventional variables on anthropometric long-term development in glutaric aciduria type 1: A national prospective multi-centre study

Glutaric aciduria type 1 (GA1) is a rare neurometabolic disorder, caused by inherited deficiency of glutaryl-CoA dehydrogenase, mostly affecting the brain. Early identification by newborn screening (NBS) significantly improves neurologic outcome. It has remained unclear whether recommended therapy, particular low lysine diet, is safe or negatively affects anthropometric long-term outcome. This national prospective, observational, multi-centre study included 79 patients identified by NBS and investigated effects of interventional and non-interventional parameters on body weight, body length, body mass index (BMI) and head circumference as well as neurological parameters. Adherence to recommended maintenance and emergency treatment (ET) had a positive impact on neurologic outcome and allowed normal anthropometric development until adulthood. In contrast, non-adherence to ET, resulting in increased risk of dystonia, had a negative impact on body weight (mean SDS -1.07; P = .023) and body length (mean SDS -1.34; P = -.016). Consistently, longitudinal analysis showed a negative influence of severe dystonia on weight and length development over time (P < .001). Macrocephaly was more often found in female (mean SDS 0.56) than in male patients (mean SDS -0.20; P = .049), and also in individuals with high excreter phenotype (mean SDS 0.44) compared to low excreter patients (mean SDS -0.68; P = .016). In GA1, recommended long-term treatment is effective and allows for normal anthropometric long-term development up to adolescence, with gender- and excreter type-specific variations. Delayed ET and severe movement disorder result in poor anthropometric outcome.

Inconsistencies in the Nutrition Management of Glutaric Aciduria Type 1: An International Survey

Glutaric aciduria type 1 (GA-1) is a cerebral organic aciduria characterized by striatal injury and progressive movement disorder. Nutrition management shifted from a general restriction of intact protein to targeted restriction of lysine and tryptophan. Recent guidelines advocate for a low-lysine diet using lysine-free, tryptophan-reduced medical foods. GA-1 guideline recommendations for dietary management of patients over the age of six are unclear, ranging from avoiding excessive intake of intact protein to counting milligrams of lysine intake. A 22–question survey on the nutrition management of GA-1 was developed with the goal of understanding approaches to diet management for patients identified by newborn screening under age six years compared to management after diet liberalization, as well as to gain insight into how clinicians define diet liberalization. Seventy-six responses (25% of possible responses) to the survey were received. Nutrition management with GA-1 is divergent among surveyed clinicians. There was congruency among survey responses to the guidelines, but there is still uncertainty about how to counsel patients on diet optimization and when diet liberalization should occur. Ongoing clinical research and better understanding of the natural history of this disease will help establish stronger recommendations from which clinicians can best counsel families.

Functional Recovery of a GCDH Variant Associated to Severe Deflavinylation—Molecular Insights into Potential Beneficial Effects of Riboflavin Supplementation in Glutaric Aciduria-Type I Patients

Riboflavin is the biological precursor of two important flavin cofactors—flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN)—that are critical prosthetic groups in several redox enzymes. While dietary supplementation with riboflavin is a recognized support therapy in several inborn errors of metabolism, it has yet unproven benefits in several other pathologies affecting flavoproteins. This is the case for glutaric aciduria type I (GA-I), a rare neurometabolic disorder associated with mutations in the GCDH gene, which encodes for glutaryl-coenzyme A (CoA) dehydrogenase (GCDH). Although there are a few reported clinical cases that have responded to riboflavin intake, there is still not enough molecular evidence supporting therapeutic recommendation. Hence, it is necessary to elucidate the molecular basis in favor of riboflavin supplementation in GA-I patients. Here, using a combination of biochemical and biophysical methodologies, we investigate the clinical variant GCDH-p.Val400Met as a model for a phenotype associated with severe deflavinylation. Through a systematic analysis, we establish that recombinant human GCDH-p.Val400Met is expressed in a nonfunctional apo form, which is mainly monomeric rather than tetrameric. However, we show that exogenous FAD is a driver for structural reorganization of the mutant enzyme with concomitant functional recovery, improved thermolability, and resistance to trypsin digestion. Overall, these results establish proof of principle for the beneficial effects of riboflavin supplementation in GA-I patients.

Short-chain fatty acid, acylation and cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Metabolic dysfunction is a fundamental core mechanism underlying CVDs. Previous studies generally focused on the roles of long-chain fatty acids (LCFAs) in CVDs. However, a growing body of study has implied that short-chain fatty acids (SCFAs: namely propionate, malonate, butyrate, 2-hydroxyisobutyrate (2-HIBA), β-hydroxybutyrate, crotonate, succinate, and glutarate) and their cognate acylations (propionylation, malonylation, butyrylation, 2-hydroxyisobutyrylation, β-hydroxybutyrylation, crotonylation, succinylation, and glutarylation) participate in CVDs. Here, we attempt to provide an overview landscape of the metabolic pattern of SCFAs in CVDs. Especially, we would focus on the SCFAs and newly identified acylations and their roles in CVDs, including atherosclerosis, hypertension, and heart failure.

Adult-onset glutaric aciduria type I: rare presentation of a treatable disorder

Glutaric aciduria type I (GA1; OMIM #231670) is an autosomal recessively inherited and treatable disorder characterized by the accumulation and irregular excretion of glutaric acid due to a defect in the glutaryl-CoA dehydrogenase enzyme involved in the catabolic pathways of L-lysine, L-hydroxylysine, and L-tryptophan. Glutaryl-CoA dehydrogenase is encoded by the GCDH gene (OMIM #608801), and several mutations in this gene are known to result in GA1. GA1 usually presents in the first 18-36 months of life with mild or severe acute encephalopathy, movement disorders, and striatal degeneration. Few cases of adult-onset GA1 have been described so far in the literature, often with non-specific and sometimes longstanding neurological symptoms. Since a preventive metabolic treatment is available, neurologists must be aware of this rare but likely underdiagnosed presentation, especially when typical neuroimaging features are identified. Here, we describe 35-year-old presenting with headache and subjective memory problems. There was no history of dystonic movement disorders. Neurological examination and neurocognitive tests were normal. Brain MRI scan revealed white matter abnormalities associated with subependymal nodules and mild frontotemporal hypoplasia suggestive of glutaric aciduria type 1 (GA1). Genetic testing confirmed the presence of homozygous c.1204C > T (p.R402W) variant in the GCDH gene, inherited from heterozygous parents.

Treatable Inherited Movement Disorders in Children: Spotlight on Clinical and Biochemical Features

Background

About 80% of monogenic metabolic diseases causing movement disorders (MDs) emerges during the first 2 decades of life, and a number of these conditions offers the opportunity of a disease-modifying treatment. The implementation of enlarged neonatal screening programs and the impressive rapid increase of the identification of new conditions are enhancing our potential to recognize and treat several diseases causing MDs, changing their outcome and phenotypic spectrum.

Methods and Findings

A literature review of monogenic disorders causing MDs amenable to treatment was conducted focusing on early clinical signs and diagnostic biomarkers. A classification in 3 broad categories based on the therapeutic approach has been proposed. Some disorders result in irreversible neurotoxic lesions that can only be prevented if treated in a presymptomatic stage, and others present with a progressive neurological impairment that a timely diagnosis and treatment may reverse or improve. Some MDs are the result of the failure of intracellular energy supply or altered glucose transport. The treatment in these conditions includes vitamins or a metabolic shift from a carbohydrate to a fatty acid catabolism, respectively. Finally, a group of highly treatable MDs are the result of defects of neurotransmitter metabolism. In these disorders, the supplementation of precursors or mimetics of neurotransmitters can deeply change the disease natural history.

Conclusions

To prevent serious and irreversible neurological impairment, the diagnostic work-up of MDs in children should consider a number of clinical red flags and biomarkers denoting specifically treatable diseases.

Clinical, biochemical, neuroradiological and molecular characterization of Egyptian patients with glutaric acidemia type 1

Glutaric acidemia type 1 (GA1) is an inherited metabolic autosomal recessive disorder that is caused by a deficiency in glutaryl-CoA dehydrogenase (GCDH). Untreated patients suffer primarily from severe striatal damage. More than 250 variants in the GCDH gene have been reported with a variable frequency among different ethnic groups. In this study, we aimed to characterize 89 Egyptian patients with GA1 and identify the variants in the 41 patients who were available for genotyping. All of our patients demonstrated clinical, neuroradiological, and biochemical characteristics that are consistent with a diagnosis of GA1. All patients presented with variable degrees of developmental delay ranging from mild to severe. Most of the 89 patients presented with acute onset type (71.9%), followed by insidious (19%) and asymptomatic (9%). A delay in diagnosis was inversely associated with macrocephaly. The prevalence rate ratio (PR) for macrocephaly that was associated with each 6-month delay was 0.95 (95%CI 0.91-0.99). However, high body weight was associated with a higher likelihood of having macrocephaly (PR 1.16, 95%CI 1.06-1.26 per 1 SD increment of Z score weight). However, body weight was inversely associated with the morbidity score. Consanguinity level was 64% among our patient's cohort and was positively associated with the C5DC level (β (95%CI) 1.06 (0.12-1.99)). Forty-one patients were available for genotyping and were sequenced for the GCDH gene. We identified a total of 25 variants, of which the following six novel variants were identified: three missense variants, c.320G > T (p.Gly107Val), c.481C > T (p.Arg161Trp) and c.572 T > G (p.Met191Arg); two deletions, c.78delG (p.Ala27Argfs34) and c.1035delG (p.Gly346Alafs*11); and one indel, c.272_331del (p.Val91_Lys111delinsGlu). All of the novel variants were absent in the 300 normal chromosomes. The most common variant, c.*165A > G, was detected in 42 alleles, and the most commonly detected missense variant, c.1204C > T (p.Arg402Trp), was identified in 29 mutated alleles in 15/41 (34.2%) of patients. Our findings suggest that GA1 is not uncommon organic acidemia disease in Egypt; therefore, there is a need for supporting neonatal screening programs in Egypt.

Genetic mimics of cerebral palsy

The term "cerebral palsy mimic" is used to describe a number of neurogenetic disorders that may present with motor symptoms in early childhood, resulting in a misdiagnosis of cerebral palsy. Cerebral palsy describes a heterogeneous group of neurodevelopmental disorders characterized by onset in infancy or early childhood of motor symptoms (including hypotonia, spasticity, dystonia, and chorea), often accompanied by developmental delay. The primary etiology of a cerebral palsy syndrome should always be identified if possible. This is particularly important in the case of genetic or metabolic disorders that have specific disease-modifying treatment. In this article, we discuss clinical features that should alert the clinician to the possibility of a cerebral palsy mimic, provide a practical framework for selecting and interpreting neuroimaging, biochemical, and genetic investigations, and highlight selected conditions that may present with predominant spasticity, dystonia/chorea, and ataxia. Making a precise diagnosis of a genetic disorder has important implications for treatment, and for advising the family regarding prognosis and genetic counseling. © 2019 International Parkinson and Movement Disorder Society.

Patterns, evolution, and severity of striatal injury in insidious- vs acute-onset glutaric aciduria type 1

BACKGROUND

Striatal injury in patients with glutaric aciduria type 1 (GA1) results in a complex, predominantly dystonic, movement disorder. Onset may be acute following acute encephalopathic crisis (AEC) or insidious without apparent acute event.

METHODS

We analyzed clinical and striatal magnetic resonance imaging (MRI) findings in 21 symptomatic GA1 patients to investigate if insidious- and acute-onset patients differed in timing, pattern of striatal injury, and outcome.

RESULTS

Eleven patients had acute and ten had insidious onset, two with later AEC (acute-on-insidious). The median onset of dystonia was 10 months in both groups, and severity was greater in patients after AEC (n = 8 severe, n = 5 moderate) than in insidious onset (n = 4 mild, n = 3 moderate, n = 1 severe). Deviations from guideline-recommended basic metabolic treatment were identified in six insidious-onset patients. Striatal lesions were extensive in all acute-onset patients and restricted to the dorsolateral putamen in eight of ten insidious-onset patients. After AEC, the two acute-on-insidious patients had extensive striatal changes superimposed on pre-existing dorsolateral putaminal lesions. Two insidious-onset patients with progressive dystonia without overt AEC also had extensive striatal changes, one with sequential striatal injury revealed by diffusion-weighted imaging. Insidious-onset patients had a latency phase of 3.5 months to 6.5 years between detection and clinical manifestation of dorsolateral putaminal lesions.

CONCLUSIONS

Insidious-onset type GA1 is characterized by dorsolateral putaminal lesions, less severe dystonia, and an asymptomatic latency phase, despite already existing lesions. Initially normal MRI during the first months and deviations from guideline-recommended treatment in a large proportion of insidious-onset patients substantiate the protective effect of neonatally initiated treatment.

Molecular genetic study of glutaric aciduria, type I: Identification of a novel mutation

Glutaric acidemia type I (GA-1) is an inborn error of metabolism due to deficiency of glutaryl-CoA dehydrogenase (GCDH), which catalyzes the conversion of glutaryl-CoA to crotonyl-CoA. GA-1 occurs in about 1 in 100 000 infants worldwide. The GCDH gene is on human chromosome 19p13.2, spans about 7 kb and comprises 11 exons and 10 introns. Tandem mass spectrometry (MS/MS) was used for clinical diagnosis in a proband from Iran with GA-1. Sanger sequencing was performed using primers specific for coding exons and exon-intron flanking regions of the GCDH gene in the proband. Cosegregation analysis and in silico assessment were performed to confirm the pathogenicity of the candidate variant. A novel homozygous missense variant c.1147C > A (p.Arg383Ser) in exon 11 of GCDH was identified. Examination of variant through in silico software tools determines its deleterious effect on protein in terms of function and stability. The variant cosegregates with the disease in family. In this study, the clinical and molecular aspects of GA-1 were investigated, which showed one novel mutation in the GCDH gene in an Iranian patient. The variant is categorized as pathogenic according to the the guideline of the American College of Medical Genetics and Genomics (ACMG) for variant interpretation. This mutation c.1147C > A (p.Arg383Ser) may also be prevalent among Iranian populations.

Patterns, evolution, and severity of striatal injury in insidious- versus acute-onset glutaric aciduria type 1

BACKGROUND

Striatal injury in patients with glutaric aciduria type 1 (GA1) results in a complex, predominantly dystonic, movement disorder. Onset may be acute following acute encephalopathic crisis (AEC) or insidious without apparent acute event.

METHODS

We analyzed clinical and striatal magnetic resonance imaging (MRI) findings in 21 symptomatic GA1 patients to investigate if insidious- and acute-onset patients differed in timing, pattern of striatal injury, and outcome.

RESULTS

Eleven patients had acute and ten had insidious onset, two with later AEC (acute-on-insidious). The median onset of dystonia was 10 months in both groups, and severity was greater in patients after AEC (n = 8 severe, n = 5 moderate) than in insidious onset (n = 4 mild, n = 3 moderate, n = 1 severe). Deviations from guideline-recommended basic metabolic treatment were identified in six insidious-onset patients. Striatal lesions were extensive in all acute-onset patients and restricted to the dorsolateral putamen in eight of ten insidious-onset patients. After AEC, the two acute-on-insidious patients had extensive striatal changes superimposed on pre-existing dorsolateral putaminal lesions. Two insidious-onset patients with progressive dystonia without overt AEC also had extensive striatal changes, one with sequential striatal injury revealed by diffusion-weighted imaging. Insidious-onset patients had a latency phase of 3.5 months to 6.5 years between detection and clinical manifestation of dorsolateral putaminal lesions.

CONCLUSIONS

Insidious-onset type GA1 is characterized by dorsolateral putaminal lesions, less severe dystonia, and an asymptomatic latency phase, despite already existing lesions. Initially normal MRI during the first months and deviations from guideline-recommended treatment in a large proportion of insidious-onset patients substantiate the protective effect of neonatally initiated treatment.

Movement Disorders and Neurometabolic Diseases

Many inherited metabolic diseases or inborn errors of metabolism (IEM) cause movement disorders in children. This review focuses on chorea, dystonia, myoclonus, tremor, and parkinsonism. Broad neurometabolic categories commonly responsible for pediatric movement disorders include mitochondrial cytopathies, organic acidemias, mineral metabolism and transport disorders, neurotransmitter diseases, purine metabolism abnormalities, lipid storage conditions, and creatine metabolism dysfunction. Each movement disorder can be caused by many IEM and several of them can cause multiple movement abnormalities. Dietary modifications, medications, and increasingly specific therapy can improve outcomes in children with movement disorders caused by IEM. Recognition and characterization of secondary movement disorders in children facilitate their management and diagnosis, and possible treatment of an underlying IEM.

Genotype-phenotype correlation in 18 Egyptian patients with glutaric acidemia type I

Glutaric acidemia I (GAI) is an autosomal recessive metabolic disease caused by a deficiency of glutaryl-CoA dehydrogenase enzyme (GCDH). Patients with GAI are characterized by macrocephaly, acute encephalitis-like crises, dystonia and frontotemporal atrophy. In this study, we investigated 18 Egyptian patients that were diagnosed with GAI based on their clinical, neuroradiological, and biochemical profiles. Of the 18 patients, 16 had developmental delay and/or regression, dystonia was prominent in 75% of the cases, and three patients died. Molecular genetics analysis identified 14 different mutations in the GCDH gene in the 18 patients, of the 14 mutations, nine were missense, three were in the 3'-Untranslated Region (3'-UTR), one was nonsense, and one was a silent mutation. Four novel mutations were identified (c.148 T > A; p.Trp50Arg, c.158C > A; p.Pro53Gln, c.1284C > G; p.Ile428Met, and c.1189G > T; p.Glu397*) that were all absent in 300 normal chromosomes. The 3'-UTR mutation (c.*165A > G; rs8012), was the most frequent mutation observed (0.5; 18/36), followed by the most common mutation among Caucasian patients (p.Arg402Trp; rs121434369) with allele frequency of 0.36 (13/36), and the 3'-UTR mutation (c.*288G > T; rs9384, 0.22; 8/16). The p.Arg257Gln mutation was found with allele frequency of ~0.17 (6/36). The marked homozygosity observed in our patients is probably due to the high level of consanguinity that is observed in 100% of the cases. We used nine in silico prediction tools to predict the pathogenicity (SIFT, PhD-SNP, SNAP, Meta-SNP, PolyPhen2, and Align GVGD) and protein stability (I-Mutant2.0, Mupro, and istable) of the nine missense mutants. The mutant p.Arg402Trp was predicted to be most deleterious by all the six pathogenicity prediction tools and destabilizing by all the three-stability prediction tools, and highly conserved by the ConSurf server. Using the clinical, biochemical, family history of the 18 patients, and the in silico analysis of the missense mutations, our study showed a mix of conclusive and inconclusive genotype-phenotype correlations among our patient's cohort and suggests the usefulness of using various sophisticated computational analysis to be utilized for future variant classifications in the genetic clinics.

Severe neurological manifestations in an Egyptian patient with a novel frameshift mutation in the Glutaryl-CoA dehydrogenase gene

To characterize an Egyptian patient with glutaric acidemia type I (GA I) and to identify the causative mutation(s) that may be responsible for the disease phenotype. MRI was performed on the patient using the 1.5 T magnet, biochemical analysis was carried out using gas chromatography/mass spectrometry on the patient's dried blood spot, and the patient's organic acids were measured in dried blood and a urine sample using MS/MS and GC/MS, respectively. Total RNA was isolated from the patient's peripheral blood, and the synthesized cDNA was bi-directionally sequenced. The patient exhibited clinical features and MRI findings compatible with a diagnosis of GA I. The abnormal elevation of organic acids in the urine supported the presence of glutaryl-CoA dehydrogenase deficiency. Gene sequencing revealed a novel homozygous frameshift mutation, c.644_645insCTCG; p.(Pro217Leufs*14), in exon 8 of the GCDH gene. The present study revealed a novel frameshift mutation responsible for a severe GA I phenotype in an Egyptian patient. This novel mutation will ultimately contribute to a better understanding of the molecular pathology of the disease and shed light on the intricacies of the genotype-phenotype correlation of GA I disease.

Proposed recommendations for diagnosing and managing individuals with glutaric aciduria type I: second revision

Glutaric aciduria type I (GA-I; synonym, glutaric acidemia type I) is a rare inherited metabolic disease caused by deficiency of glutaryl-CoA dehydrogenase located in the catabolic pathways of L-lysine, L-hydroxylysine, and L-tryptophan. The enzymatic defect results in elevated concentrations of glutaric acid, 3-hydroxyglutaric acid, glutaconic acid, and glutaryl carnitine in body tissues, which can be reliably detected by gas chromatography/mass spectrometry (organic acids) and tandem mass spectrometry (acylcarnitines). Most untreated individuals with GA-I experience acute encephalopathic crises during the first 6 years of life that are triggered by infectious diseases, febrile reaction to vaccinations, and surgery. These crises result in striatal injury and consequent dystonic movement disorder; thus, significant mortality and morbidity results. In some patients, neurologic disease may also develop without clinically apparent crises at any age. Neonatal screening for GA-I us being used in a growing number of countries worldwide and is cost effective. Metabolic treatment, consisting of low lysine diet, carnitine supplementation, and intensified emergency treatment during catabolism, is effective treatment and improves neurologic outcome in those individuals diagnosed early; treatment after symptom onset, however, is less effective. Dietary treatment is relaxed after age 6 years and should be supervised by specialized metabolic centers. The major aim of this second revision of proposed recommendations is to re-evaluate the previous recommendations (Kölker et al. J Inherit Metab Dis 30:5-22, 2007b; J Inherit Metab Dis 34:677-694, 2011) and add new research findings, relevant clinical aspects, and the perspective of affected individuals.

Glutaric Aciduria Type I: A Rare Metabolic Disorder Mimicking as Choreoathetoid Cerebral Palsy

Glutaric aciduria type I (GA I) is an autosomal recessive inborn error of metabolism caused by a deficiency of the enzyme glutaryl-CoA dehydrogenase. This disorder is characterized by progressive dystonia, choreoathetosis, and dyskinesia. It is often misdiagnosed as athetoid cerebral palsy. Laboratory evaluation usually demonstrates increased urinary excretion of gluataric acid and 3-hydroxyglutaric acid. We report a case of a 7-year-old boy presenting with choreoathetosis and dystonia, mimicking as choreoathetoid cerebral palsy. The presence of characteristic neuroimaging and biochemical studies led to the diagnosis of GA I.

Review and evaluation of the methodological quality of the existing guidelines and recommendations for inherited neurometabolic disorders

BACKGROUND

Inherited neurometabolic disorders (iNMDs) represent a group of almost seven hundred rare diseases whose common manifestations are clinical neurologic or cognitive symptoms that can appear at any time, in the first months/years of age or even later in adulthood. Early diagnosis and timely treatments are often pivotal for the favorable course of the disease. Thus, the elaboration of new evidence-based recommendations for iNMD diagnosis and management is increasingly requested by health care professionals and patients, even though the methodological quality of existing guidelines is largely unclear. InNerMeD-I-Network is the first European network on iNMDs that was created with the aim of sharing and increasing validated information about diagnosis and management of neurometabolic disorders. One of the goals of the project was to determine the number and the methodological quality of existing guidelines and recommendations for iNMDs.

METHODS

We performed a systematic search on PubMed, the National Guideline Clearinghouse (NGC), the Guidelines International Network (G-I-N), the Scottish Intercollegiate Guideline Network (SIGN) and the National Institute for Health and Care Excellence (NICE) to identify all the published guidelines and recommendations for iNMDs from January 2000 to June 2015. The methodological quality of the selected documents was determined using the AGREE II instrument, an appraisal tool composed of 6 domains covering 23 key items.

RESULTS

A total of 55 records met the inclusion criteria, 11 % were about groups of disorders, whereas the majority encompassed only one disorder. Lysosomal disorders, and in particular Fabry, Gaucher disease and mucopolysaccharidoses where the most studied. The overall methodological quality of the recommendation was acceptable and increased over time, with 25 % of the identified guidelines strongly recommended by the appraisers, 64 % recommended, and 11 % not recommended. However, heterogeneity in the obtained scores for each domain was observed among documents covering different groups of disorders and some domains like 'stakeholder involvement' and 'applicability' were generally scarcely addressed.

CONCLUSIONS

Greater efforts should be devoted to improve the methodological quality of guidelines and recommendations for iNMDs and AGREE II instrument seems advisable for new guideline development. The elaboration of new guidelines encompassing still uncovered disorders is badly needed.

Clinical and molecular investigation in Chinese patients with glutaric aciduria type I

Glutaric aciduria type I (GA-I) is a rare autosomal recessive metabolic disorder caused by deficiency of glutaryl-CoA dehydrogenase (GCDH), leading to an abnormal metabolism of lysine, hydroxylysine and tryptophan. It results in accumulations of glutaric acid, 3-hydroxyglutaric acid and glutaconic acid. Clinical features include the sudden onset of encephalopathy, hypotonia and macrocephaly usually before age 18months. Here we report five cases of GA-I confirmed with mutation analysis. GCDH gene mutations were identified in all five probands with GA-I. Three of them had compound heterozygous mutations and two had homozygous mutations. Mutations of two alleles (c.334G>T and IVS11-11A>G) were novel and both of them were confirmed to be splice site mutations by reverse transcription PCR.

(1)H-MRS in glutaric aciduria type 1: impact of biochemical phenotype and age on the cerebral accumulation of neurotoxic metabolites

BACKGROUND

In glutaric aciduria type 1 (GA1) the neurotoxic metabolites glutaric acid (GA) and 3-hydroxyglutaric acid (3-OH-GA) accumulate within the brain. Due to limited efflux across the blood-brain-barrier biochemical monitoring of intracerebrally accumulating toxic metabolites is as yet not possible.

AIMS

To investigate brain metabolic patterns in glutaric aciduria type 1 using (1)H magnetic resonance spectroscopy ((1)H-MRS) with focus on detecting the disease-related neurotoxic metabolites GA and 3-OH-GA.

PATIENTS AND METHODS

Short echo time (1)H-MRS was performed in 13 treated metabolically stable patients. Twenty-one white matter and 16 basal ganglia spectra from 12 patients (age range 7 months - 22 years) were included. Subgroups based on age, biochemical phenotype and/or associated MRI changes were compared with control spectra.

RESULTS

GA was elevated in white matter of patients. 3-OH-GA was elevated in white matter of older patients with associated signal changes on MRI, which was structurally characterized by decreased creatine and phosphocreatine (tCr) and elevated choline (Cho). Metabolite changes differed with biochemical phenotype and disease duration: Low excretors with up to 30% residual enzyme activity had only mildly, non-significantly elevated GA and mildly subnormal N-acetylaspartate (tNAA). High excretors with complete lack of enzyme activity had significantly increased GA, tNAA was mildly subnormal in younger and decreased in older high excretors.

CONCLUSIONS

GA and 3-OH-GA are detectable by in vivo (1)H-MRS, which might finally allow biochemical follow-up monitoring of intracerebrally accumulating neurotoxic metabolites in GA1. A high excreting phenotype appears to be a risk factor for cerebral GA accumulation and progressive neuroaxonal compromise despite a similar clinical course in younger high and low excreting patients. This might have consequences for long-term outcome.

Compartmentation of Metabolism of the C12-, C9-, and C5-n-dicarboxylates in Rat Liver, Investigated by Mass Isotopomer Analysis: ANAPLEROSIS FROM DODECANEDIOATE

We investigated the compartmentation of the catabolism of dodecanedioate (DODA), azelate, and glutarate in perfused rat livers, using a combination of metabolomics and mass isotopomer analyses. Livers were perfused with recirculating or nonrecirculating buffer containing one fully (13)C-labeled dicarboxylate. Information on the peroxisomal versus mitochondrial catabolism was gathered from the labeling patterns of acetyl-CoA proxies, i.e. total acetyl-CoA, the acetyl moiety of citrate, C-1 + 2 of β-hydroxybutyrate, malonyl-CoA, and acetylcarnitine. Additional information was obtained from the labeling patterns of citric acid cycle intermediates and related compounds. The data characterize the partial oxidation of DODA and azelate in peroxisomes, with terminal oxidation in mitochondria. We did not find evidence of peroxisomal oxidation of glutarate. Unexpectedly, DODA contributes a substantial fraction to anaplerosis of the citric acid cycle. This opens the possibility to use water-soluble DODA in nutritional or pharmacological anaplerotic therapy when other anaplerotic substrates are impractical or contraindicated, e.g. in propionic acidemia and methylmalonic acidemia.

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

Networking Across Borders for Individuals with Organic Acidurias and Urea Cycle Disorders: The E-IMD Consortium

BACKGROUND

Patients with organic acidurias (OAD) and urea cycle disorders (UCD) are at increased risk of disability, impaired quality of life and reduced life expectancy. Clinical care in any one centre is constrained by small patient numbers; and furthermore diagnostic and treatment strategies vary between metabolic centres and countries, resulting in significant inequalities and disparity in patient outcome.

AIMS/METHODS

The overall objective of the EU-funded activity 'European registry and network for intoxication type metabolic diseases' (E-IMD) is to collect systematic data to improve the knowledge of these diseases, to develop consensus care guidelines and to provide detailed information materials for families and professionals.

RESULTS

Within three years E-IMD has (1) established a network of 87 partners in 25 countries (2) set up a patient registry of more than 1,000 individuals with OAD and UCD, (3) launched a website ( www.e-imd.org ) including detailed information materials in 11 languages, (4) developed guidelines for OAD and UCD, (5) organised two teaching courses and various scientific meetings, (6) extended the IT platform clustering with other inherited metabolic diseases (IMD) and (7) strengthened the collaboration with other international scientific consortia.

CONCLUSIONS

E-IMD has made important steps towards improving and sharing knowledge on OAD and UCD and harmonisation of diagnostic and therapeutic strategies. Through the establishment of a modular patient registry, clustering with other IMD and stepwise extension of the network, E-IMD has implemented the core components of a European Reference Network for rare diseases.

Molecular analysis of Cypriot patients with Glutaric aciduria type I: identification of two novel mutations

OBJECTIVES

The purpose of this study was to identify the mutations in the glutaryl-CoA dehydrogenase gene (GCDH) in ten Cypriot patients with Glutaric aciduria type I (GAI).

DESIGN AND METHODS

Molecular analysis of the GCDH gene was performed by direct sequencing of the patients' genomic DNA. In silico tools were applied to predict the effect of the novel variants on the structure and function of the protein.

RESULTS

All disease alleles were characterized (mutation detection rate 100%). Five missense mutations were identified: c.192G>T (p.Glu64Asp) and c.803G>T (p.Gly268Val), which are novel, and three previously described mutations, c.1123T>C (p.Cys375Arg), c.1204C>T (p.Arg402Trp) and c.1286C>T (p.Thr429Met).

CONCLUSIONS

Two novel mutations, p.Glu64Asp and p.Gly268Val, account for the majority of disease alleles (76.5%) in Cypriot patients with Glutaric aciduria type I. A founder effect for the p.Glu64Asp and the p.Gly268Val can be suggested based on the place of origin of the carriers of these mutations. Identification of the causative mutations of GAI in Cypriot patients will facilitate carrier detection as well as post- and pre-natal diagnosis.

Newborn screening by tandem mass spectrometry for glutaric aciduria type 1: a cost-effectiveness analysis

BACKGROUND

Glutaric aciduria type I (GA-I) is a rare metabolic disorder caused by inherited deficiency of glutaryl-CoA dehydrogenase. Despite high prognostic relevance of early diagnosis and start of metabolic treatment as well as an additional cost saving potential later in life, only a limited number of countries recommend newborn screening for GA-I. So far only limited data is available enabling health care decision makers to evaluate whether investing into GA-I screening represents value for money. The aim of our study was therefore to assess the cost-effectiveness of newborn screening for GA-I by tandem mass spectrometry (MS/MS) compared to a scenario where GA-I is not included in the MS/MS screening panel.

METHODS

We assessed the cost-effectiveness of newborn screening for GA-I against the alternative of not including GA-I in MS/MS screening. A Markov model was developed simulating the clinical course of screened and unscreened newborns within different time horizons of 20 and 70 years. Monte Carlo simulation based probabilistic sensitivity analysis was used to determine the probability of GA-I screening representing a cost-effective therapeutic strategy.

RESULTS

Within a 20 year time horizon, GA-I screening averts approximately 3.7 DALYs (95% CI 2.9 - 4.5) and about one life year is gained (95% CI 0.7 - 1.4) per 100,000 neonates screened initially . Moreover, the screening programme saves a total of around 30,682 Euro (95% CI 14,343 to 49,176 Euro) per 100,000 screened neonates over a 20 year time horizon.

CONCLUSION

Within the limitations of the present study, extending pre-existing MS/MS newborn screening programmes by GA-I represents a highly cost-effective diagnostic strategy when assessed under conditions comparable to the German health care system.

Glutaric aciduria type I: outcome of patients with early- versus late-diagnosis

Patients with Glutaric aciduria type 1 (GA-1) can be identified by newborn screening using tandem mass spectrometry. The clinical evolution of screened patients seems to be more favourable compared with those diagnosed later, although long-term evolution is still doubtful. We have evaluated the outcome in nine GA-1 patients diagnosed in our region during 12 years. Six were detected by newborn screening and 3 clinically. The birth prevalence was 1:35,027. High blood C5DC concentration, in 8/9 patients, was found, whereas all patients exhibited high concentration of this metabolite in urine. Therefore, urine C5DC was a good marker for the detection of this disease. Eight different mutations in the GCDH gene were identified, four of them were novel (p.R88H, p.Y398C, p.R372K, p.D220N); being p.R227P the mostcommon. Macrocephaly with enlarged frontotemporal subarachnoid space was present in 4/6 patients diagnosed by newborn screening, all these patients required high energy intake, and in two cases, enteral feeding during the first year of life was needed. One child had an intercurrent episode of feeding refuse with hypoglycemia at two years of age. The mean follow-up time of screened patients was 56 months, and patients still remain asymptomatic. However, after a mean follow-up of 97 months treatment efficacy was poor in unscreened patients, two of them showing a severe spastic tetraparesis. Plasma levels of lysine, tryptophan and carnitine, were the most useful biomarkers for the follow-up. Our data support that, early diagnosis and treatment strategies are essential measures for the good clinical evolution of GA-1 patients.

Low lysine diet in glutaric aciduria type I--effect on anthropometric and biochemical follow-up parameters

BACKGROUND

Metabolic treatment in glutaric aciduria type I (GA-I) including a low lysine diet with lysine-free, tryptophan-reduced amino acid supplements (AAS), carnitine supplementation and early start of emergency treatment during putatively threatening episodes of intermittent febrile illness dramatically improves the outcome and thus has been recommended by an international guideline group (Kölker et al, J Inherit Metab Dis 30:5-22, 2007). However, possible affection of linear growth, weight gain and biochemical follow-up monitoring has not been studied systematically.

METHODS

Thirty-three patients (n = 29 asymptomatic, n = 4 dystonic) with GA-I who have been identified by newborn screening in Germany from 1999 to 2009 were followed prospectively during the first six years of life. Dietary treatment protocols, anthropometrical and biochemical parameters were longitudinally evaluated.

RESULTS

Mean daily intake as percentage of guideline recommendations was excellent for lysine (asymptomatic patients: 101 %; dystonic patients: 103 %), lysine-free, tryptophan-reduced AAS (108 %; 104 %), energy (106 %; 110 %), and carnitine (92 %; 102 %). Low lysine diet did not affect weight gain (mean SDS 0.05) but mildly impaired linear growth in asymptomatic patients (mean SDS -0.38), while dystonic patients showed significantly reduced weight gain (mean SDS -1.32) and a tendency towards linear growth retardation (mean SDS -1.03). Patients treated in accordance with recent recommendations did not show relevant abnormalities of routine biochemical follow-up parameters.

INTERPRETATION

Low lysine diet promotes sufficient intake of essential nutrients and anthropometric development in asymptomatic children up to age 6 year, whereas individualized nutritional concepts are required for dystonic patients. Revised recommendations for biochemical monitoring might be required for asymptomatic patients.

Neurotoxic effects of trans-glutaconic acid in rats

trans-Glutaconic acid (tGA) is an unsaturated C5-dicarboxylic acid which may be found accumulated in glutaric aciduria type I, whose pathophysiology is still uncertain. In the present work it was investigated the in vitro effect of increasing tGA concentrations on neurochemical and oxidative stress parameters in rat cerebral cortex. We observed that Na⁺, K⁺-ATPase activity was reduced by tGA, but not creatine kinase, respiratory chain complex IV, and ATP synthase activities. On the other hand, tGA significantly increased lipid peroxidation (thiobarbituric acid-reactive species levels and spontaneous chemiluminescence), as well as protein oxidative damage (oxidation of sulfhydryl groups). tGA also significantly decreased nonenzymatic antioxidant defenses (TRAP and reduced glutathione levels). Our data suggest that tGA may be neurotoxic in rat brain.

Ammonium accumulation and cell death in a rat 3D brain cell model of glutaric aciduria type I

Glutaric aciduria type I (glutaryl-CoA dehydrogenase deficiency) is an inborn error of metabolism that usually manifests in infancy by an acute encephalopathic crisis and often results in permanent motor handicap. Biochemical hallmarks of this disease are elevated levels of glutarate and 3-hydroxyglutarate in blood and urine. The neuropathology of this disease is still poorly understood, as low lysine diet and carnitine supplementation do not always prevent brain damage, even in early-treated patients. We used a 3D in vitro model of rat organotypic brain cell cultures in aggregates to mimic glutaric aciduria type I by repeated administration of 1 mM glutarate or 3-hydroxyglutarate at two time points representing different developmental stages. Both metabolites were deleterious for the developing brain cells, with 3-hydroxyglutarate being the most toxic metabolite in our model. Astrocytes were the cells most strongly affected by metabolite exposure. In culture medium, we observed an up to 11-fold increase of ammonium in the culture medium with a concomitant decrease of glutamine. We further observed an increase in lactate and a concomitant decrease in glucose. Exposure to 3-hydroxyglutarate led to a significantly increased cell death rate. Thus, we propose a three step model for brain damage in glutaric aciduria type I: (i) 3-OHGA causes the death of astrocytes, (ii) deficiency of the astrocytic enzyme glutamine synthetase leads to intracerebral ammonium accumulation, and (iii) high ammonium triggers secondary death of other brain cells. These unexpected findings need to be further investigated and verified in vivo. They suggest that intracerebral ammonium accumulation might be an important target for the development of more effective treatment strategies to prevent brain damage in patients with glutaric aciduria type I.

Biochemical screening of 504,049 newborns in Denmark, the Faroe Islands and Greenland--experience and development of a routine program for expanded newborn screening

Expanded newborn screening for selected inborn errors of metabolism (IEM) in Denmark, the Faroe Islands and Greenland was introduced in 2002. We now present clinical, biochemical, and statistical results of expanded screening (excluding PKU) of 504,049 newborns during nine years as well as diagnoses and clinical findings in 82,930 unscreened newborns born in the same period. The frequencies of diagnoses made within the panel of disorders screened for are compared with the frequencies of the disorders in the decade preceding expanded newborn screening. The expanded screening was performed as a pilot study during the first seven years, and the experience obtained during these years was used in the development of the routine neonatal screening program introduced in 2009. Methods for screening included tandem mass spectrometry and an assay for determination of biotinidase activity. A total of 310 samples from 504,049 newborns gave positive screening results. Of the 310 results, 114 were true positive, including results from 12 newborns in which the disease in question was subsequently diagnosed in their mothers. Thus, the overall frequency of an IEM in the screening panel was 1:4942 (mothers excluded) or 1:4421 (mothers included). The false positive rate was 0.038% and positive predictive value 37%. Overall specificity was 99.99%. All patients with true positive results were followed in The Center for Inherited Metabolic Disorders in Copenhagen, and the mean follow-up period was 45 months (range 2109 months). There were no deaths among the 102 children, and 94% had no clinically significant sequelae at last follow-up. Our study confirms the higher frequency of selected IEM after implementation of expanded newborn screening and suggests an improved outcome for several disorders. We argue that newborn screening for these disorders should be standard of care, though unresolved issues remain, e.g. about newborns with a potential for remaining asymptomatic throughout life. Well organized logistics of the screening program from screening laboratory to centralized, clinical management is important.

Glutaric aciduria type I: A treatable neurometabolic disorder

Background and Objectives:

Glutaric aciduria Type-I (GA-I) has characteristic clinical and neuroimaging features, which clinches the diagnosis in a majority of patients. However, there have been few case reports on GA-I from India. This study was undertaken to study the clinical presentations, metabolic profile, neuroimaging findings and outcome of patients with GA-I.

Study Design:

The present study was a retrospective study.

Materials and Methods:

Retrospective review of charts of patients with a diagnosis of GA-I was carried out from March 2008 to April 2010. The clinical, laboratory and neuroimaging findings were extracted in a predesigned proforma and the data was analyzed.

Results:

Eleven cases were found to have GA-1. Clinical presentation was quite varied. Follow-up of patients revealed that one patient with macrocephaly as the only clinical finding was developmentally normal. One patient with encephalitis-like illness steadily improved and started walking at 2 years. Two patients were bed ridden and had severe dystonia. One patient died during follow-up. The remaining six patients had dystonia and other abnormal movements, but had attained sitting without support and were not ambulatory.

Conclusion:

GA-I is not an uncommon disorder and diagnosis can be made easily based on clinical, laboratory investigations and neuroimaging findings. It is one of the treatable metabolic disorders and, if managed appropriately, favorable prognosis can be given.