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

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.

Metabolic and genetic disorders mimicking cerebral palsy

Cerebral palsy is a syndrome that encompasses a large group of childhood movement and posture disorders that result from a lesion occurring in the developing brain. The clinical presentation of many metabolic and genetic conditions, particularly in highly consanguineous populations, can mimic cerebral palsy particularly at early age. The aim of this review article is to identify the clinical features that should alert the physician to the possibility of disorders that resemble cerebral palsy, the clinical and neuroimaging red flags, and highlight some metabolic and genetic conditions which may present with spasticity, ataxia and dyskinesia. In the case of metabolic or genetic disorder, making a precise diagnosis is particularly important for the possibility of treatment, accurate prognosis and genetic counseling.

The European Phenylketonuria Guidelines and the challenges on management practices in Portugal

Background Phenylketonuria (PKU) management practices differ between and within countries. In 2007, the Portuguese Society for Metabolic Disorders (SPDM) approved the Portuguese Consensus (PC) for the nutritional treatment of PKU. The recently published European PKU Guidelines (EPG, 2017) systematically reviewed recent evidence and aimed to harmonise treatment protocols in Europe. The objective of this study was to appraise the EPG acceptance and implementation in Portuguese treatment centres. Methods An electronic questionnaire was prepared and the link was sent to 135 SPDM members. It outlined the 10 EPG key recommendations and compared each statement with the consensus recommendations published by SPDM. Responses were recorded and descriptive analyses were performed. Results Twenty-five professionals completed the questionnaire, and over half (56%) were nutritionists/dieticians. At least one questionnaire from each of the 10 national treatment centres was returned. In general, responders accepted most of the recommendations. However, only the recommendation about target phenylalanine (Phe) concentrations between 120 and 360 μmol/L for patients <12 years received 100% consensus with a further seven recommendations gaining over 70% consensus. Almost half of the professionals (48%, n = 12) required further discussion about the EPG-safe upper target blood Phe concentration (600 μmol/L) suggested for patients aged ≥12 years. Almost one third (32%, n = 8) failed to agree with the recommendation in the EPG-proposed classification of Phe hydroxylase (PAH) deficiency. Conclusions The EPG received overall good acceptance, but there was divided opinion about some recommendations which require further discussion before implementation by the Portuguese treatment centres.

Formation of 3-hydroxyglutaric acid in glutaric aciduria type I: in vitro participation of medium chain acyl-CoA dehydrogenase

3-Hydroxyglutaric acid (3-OH-GA) in urine has been identified as the most reliable diagnostic marker for glutaric aciduria type I (GA I). We showed that hydratation of glutaconyl-CoA to 3-hydroxyglutaryl-CoA, which is subsequently hydrolyzed to 3-OH-GA, is efficiently catalyzed by 3-methylglutaconyl-CoA hydratase (3-MGH). We have now investigated whether mitochondrial acyl-CoA-dehydrogenases can convert glutaryl-CoA to glutaconyl-CoA. Short-chain acyl-CoA dehydrogenase (SCAD), medium-chain acyl-CoA dehydrogenase (MCAD), and long-chain acyl-CoA dehydrogenase (LCAD) accepted glutaryl-CoA as a substrate. The highest k cat of glutaryl-CoA was found for MCAD (0.12 ± 0.01 second-1) and was about 26-fold and 52-fold higher than those of LCAD and SCAD, respectively. The turnover of MCAD for glutaryl-CoA was about 1.5% of that of its natural substrate octanoyl-CoA. Despite high K m (above 600 μM) and low turnover rate, the oxidation of glutaryl-CoA by MCAD in combination with 3-MGH could explain the urinary concentration of 3-OH-GA in GA I patients.

Ammonium accumulation and chemokine decrease in culture media of Gcdh-/- 3D reaggregated brain cell cultures

Glutaric Aciduria type I (GA-I) is caused by mutations in the GCDH gene. Its deficiency results in accumulation of the key metabolites glutaric acid (GA) and 3-hydroxyglutaric acid (3-OHGA) in body tissues and fluids. Present knowledge on the neuropathogenesis of GA-I suggests that GA and 3-OHGA have toxic properties on the developing brain. We analyzed morphological and biochemical features of 3D brain cell aggregates issued from Gcdh^-/- mice at two different developmental stages, day-in-vitro (DIV) 8 and 14, corresponding to the neonatal period and early childhood. We also induced a metabolic stress by exposing the aggregates to 10 mM l-lysine (Lys). Significant amounts of GA and 3-OHGA were detected in Gcdh^-/- aggregates and their culture media. Ammonium was significantly increased in culture media of Gcdh^-/- aggregates at the early developmental stage. Concentrations of GA, 3-OHGA and ammonium increased significantly after exposure to Lys. Gcdh^-/- aggregates manifested morphological alterations of all brain cell types at DIV 8 while at DIV 14 they were only visible after exposure to Lys. Several chemokine levels were significantly decreased in culture media of Gcdh^-/- aggregates at DIV 14 and after exposure to Lys at DIV 8. This new in vitro model for brain damage in GA-I mimics well in vivo conditions. As seen previously in WT aggregates exposed to 3-OHGA, we confirmed a significant ammonium production by immature Gcdh^-/- brain cells. We described for the first time a decrease of chemokines in Gcdh^-/- culture media which might contribute to brain cell injury in GA-I.

Mild phenotype of glutaric aciduria type 1 in polish patients - novel data from a group of 13 cases

Glutaric aciduria type 1 is a neurometabolic disorder, caused by riboflavin-dependent glutaryl-CoA dehydrogenase deficiency. As its consequence, accumulation of the putatively neurotoxic metabolites (glutaric and 3-hydroxyglutaric acids) in body tissues, but especially within the brain, is observed. Estimated incidence of the disease is 1 in 110,000 newborns, The prevalence however may be higher, depending on a specific ethnic group, and result in phenotypic variation as well. In this paper we present clinical data of 13 patients of Polish nationality. They all present a mild phenotype and clinical course of glutaric aciduria type 1. Based on their clinical data, presented herein, we like to pay attention to the phenotypic and neuroimaging features important for the diagnosis of mild form of this disease. Moreover, we present novel molecular data, which may correlate with such a manifestation.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 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.

The neuroimaging mimics of abusive head trauma

Abusive head trauma (AHT) is a significant cause of morbidity and mortality in the paediatric population, typically in children under the age of two years. Neuroimaging plays a key role in the diagnostic work up of these patients as information regarding the mechanism of injury is often lacking and the findings on examination can be nonspecific. A number of conditions, both traumatic and atraumatic can mimic AHT based on neuroimaging features alone. The repercussions associated with a diagnosis or misdiagnosis of AHT can be severe and radiologists therefore need to be aware of and familiar with the imaging differentials of AHT. In this paper we review the imaging findings of the radiological mimics of AHT and focus on features that can help differentiate these entities from AHT.

Malignant brain tumors in patients with glutaric aciduria type I

Three young patients with glutaric aciduria type I (age 6-23 years) of different ethnic origins, treated for their metabolic disease since early childhood, presented with malignant central nervous system tumors. We recommend continuing clinical follow-up, including monitoring of neurological manifestations and neuroradiological findings, in all patients with glutaric aciduria type I beyond early childhood, especially if adherence to diet is poor or the treatment was not started neonatally.

Neuroimaging Findings of Organic Acidemias and Aminoacidopathies

Although individual cases of inherited metabolic disorders are rare, overall they account for a substantial number of disorders affecting the central nervous system. Organic acidemias and aminoacidopathies include a variety of inborn errors of metabolism that are caused by defects in the intermediary metabolic pathways of carbohydrates, amino acids, and fatty acid oxidation. These defects can lead to the abnormal accumulation of organic acids and amino acids in multiple organs, including the brain. Early diagnosis is mandatory to initiate therapy and prevent permanent long-term neurologic impairments or death. Neuroimaging findings can be nonspecific, and metabolism- and genetics-based laboratory investigations are needed to confirm the diagnosis. However, neuroimaging has a key role in guiding the diagnostic workup. The findings at conventional and advanced magnetic resonance imaging may suggest the correct diagnosis, help narrow the differential diagnosis, and consequently facilitate early initiation of targeted metabolism- and genetics-based laboratory investigations and treatment. Neuroimaging may be especially helpful for distinguishing organic acidemias and aminoacidopathies from other more common diseases with similar manifestations, such as hypoxic-ischemic injury and neonatal sepsis. Therefore, it is important that radiologists, neuroradiologists, pediatric neuroradiologists, and clinicians are familiar with the neuroimaging findings of organic acidemias and aminoacidopathies. ^©RSNA, 2018.

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.

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.

Favourable outcome in a child with symptomatic diagnosis of Glutaric aciduria type 1 despite vertical HIV infection and minor head trauma

The first case of Glutaric aciduria Type 1(GA1) in an African child was reported in 2001. GA1 has a prevalence of 1:5000 in black South Africans. Although early diagnosis is essential for a favourable outcome, newborn screening is not routine in South Africa where an estimated 320,000 children have HIV infection. Neurodevelopmental delay and encephalopathy are complications of both HIV and GA1. In such a setting it is important to recognise that HIV and GA1 can occur simultaneously. We present an HIV-infected South African male child of Xhosa descent with macrocephaly who commenced combination antiretroviral therapy (ART) at 8 weeks of age in a clinical trial which included a neurodevelopmental sub-study. He developed short-lived focal seizures at 16 months after minor head trauma. Neurological examination was normal. Neuroimaging showed temporal lobe atrophy, subtle hyperintense signal change in the globus pallidus, and focal haemosiderosis in the right Sylvian fissure region. As findings were not in keeping with HIV encephalopathy, a urine metabolic screen was undertaken which suggested GA1. Genetic testing confirmed Arg293Trp mutation. He began L-carnitine and a low protein diet as a restricted diet was not practicable. At 21 months he developed pulmonary tuberculosis, requiring 6 months treatment. He did not develop any neurologic motor symptoms. Serial neurodevelopmental and neuropsychological test scores until 9 years were similar to healthy neighbourhood controls, except for mild language delay at 3½ years. Detection of GA1, probably facilitated through participation in a clinical trial, was pivotal for a favourable outcome. The concomitant use of ART and anti-tuberculous therapy in a child with GA1 appears safe.

Inborn Errors of Metabolism with Acidosis: Organic Acidemias and Defects of Pyruvate and Ketone Body Metabolism

When a child presents with high-anion gap metabolic acidosis, the pediatrician can proceed with confidence by recalling some basic principles. Defects of organic acid, pyruvate, and ketone body metabolism that present with acute acidosis are reviewed. Flowcharts for identifying the underlying cause and initiating life-saving therapy are provided. By evaluating electrolytes, blood sugar, lactate, ammonia, and urine ketones, the provider can determine the likelihood of an inborn error of metabolism. Freezing serum, plasma, and urine samples during the acute presentation for definitive diagnostic testing at the provider's convenience aids in the differential diagnosis.

Current strategies for the treatment of inborn errors of metabolism

Inborn errors of metabolism (IEMs) are a large group of inherited disorders characterized by disruption of metabolic pathways due to deficient enzymes, cofactors, or transporters. The rapid advances in the understanding of the molecular pathophysiology of many IEMs, have led to significant progress in the development of many new treatments. The institution and continued expansion of newborn screening provide the opportunity for early treatment, leading to reduced morbidity and mortality. This review provides an overview of the diverse therapeutic approaches and recent advances in the treatment of IEMs that focus on the basic principles of reducing substrate accumulation, replacing or enhancing absent or reduced enzyme or cofactor, and supplementing product deficiency. In addition, the challenges and obstacles of current treatment modalities and future treatment perspectives are reviewed and discussed.

Food triggers and inherited metabolic disorders: a challenge to the pediatrician

Several disorders should be considered in the case of newborns and infants experiencing acute or recurrent symptoms after food ingestion. Immune-mediated adverse food reactions are the most frequent and always to be considered. Nevertheless, in the extensive differential diagnosis, clinicians should also include inherited metabolic disorders (IMDs).

This review reports clinical features and diagnostic aspects of the most common IMDs that may present with acute manifestations triggered by food intake. Major focus will be amino acid and protein metabolism defects and carbohydrate disorders.

Nowadays, for many of these disorders the risk of an acute presentation triggered by food has been decreased by the introduction of expanded newborn screening (NBS). Nevertheless, clinical suspicion remains essential because some IMDs do not have still reliable markers for NBS and a false negative screening result may occur.

The aim of this review is to help pediatricians to take these rare inherited disorders into account in the differential diagnosis of acute or recurrent gastrointestinal symptoms related to food intake, which may avoid delayed diagnosis and potentially life-threatening consequences.

Early neonatal Glutaric aciduria type I hidden by perinatal asphyxia: a case report

Background

Perinatal asphyxia (PA) occurs in about 2 to 10 per 1000 live full-term births. Although neonatal epileptic seizures are observed in up to 60% of cases, PA may mimic or subtend other conditions. Hypoxia related brain injury is particularly relevant, as it may have permanent effects on neuropsychomotor development. Antepartum obstetric conditions, may, in turn, lead to hypoxic-ischemic damage to the fetus and the newborn, often underlying PA. Herein, a case of PA that hid and triggered signs and symptoms of Glutaric Aciduria type I (GA-I), is reported.

Case presentation

R.F. was born at term after prolonged labour, by induced vaginal delivery with the Kristeller manoeuvre. He presented with severe asphyxia and asystoly. Immediate cardiopulmonary resuscitation promptly restored cardiorespiratory parameters, allowing for early extubation 30 min after. During the following hours, severe axial muscle hypotonia with an increased tone of the limb extensor muscles became evident. The absence of crying and archaic reflexes persisted and there was an onset of generalized tonic or clonic seizure. First level metabolic and inflammatory markers were within the normal range. An inherited metabolic disease was then suspected, due to the persistent clinical signs of severe neurological damage without any detectable septic parameter. GA-I was assessed and specific treatment started without any clinical improvement, although ensuring adequate growth and metabolic control. Thereafter, the baby developed a severe encephalopathy with drug resistant epileptic seizures. The progression of the neurological damage and a CVC-related sepsis led him to exitus at 2 years.

Conclusions

To the best of our knowledge, this is the first case of early post-natal onset of GA-I reported in literature to date, in the absence of expanded newborn screening (NBS) programme. As expanded NBS programmes for inborn errors of metabolism have not yet been internationally adopted, we are of the opinion that such diseases may well be hidden by misleading signs and symptoms imputable to other more frequent harmful clinical conditions. Moreover, it would be advisable that neonatologists be trained to include GA-I in the differential diagnosis of neurological damage secondary to PA.

Two Uneventful Pregnancies in a Woman with Glutaric Aciduria Type 1

Glutaric aciduria type 1 (GA1) is an autosomal recessive rare disorder caused by mutations in the GCDH gene resulting in deficiency of glutaryl-CoA dehydrogenase, leading to accumulation of the amino acids lysine, hydroxylysine and tryptophan and other metabolites. The phenotypic spectrum of disease is broad. Stress caused by infection and fever and possibly pregnancy may lead to worsening of the signs and symptoms, often with uncertain recovery.We describe a case of a female patient with GA1 who had two clinically uneventful pregnancies.At the age of 11 she was diagnosed with GA1 by family screening. The cultured skin fibroblast showed reduced glutaryl-CoA dehydrogenase activity (0.16 mg protein per min).The initial diagnostic urine glutaric acid level for this patient was 1,784 μmol/mmol creatinine. Mutation analysis showed compound heterozygosity for the p.(Gly185Arg), c.553G>A in exon 7 and p.(Arg402Trp), c.1204C.T in exon 11 mutations of the GCDH.Her pregnancy at the age of 23 was complicated by pre-eclampsia and required treatment with beta-blockers. Four years later the second pregnancy was uncomplicated. The management plan during the caesarean section included intravenous dextrose and lipid infusions. The patient rapidly recovered from both surgeries.Both babies have had normal development to date. On newborn screening, plasma acylcarnitine showed a transient increase in glutarylcarnitine, and the urine organic acid analysis showed a trace of 3-hydroxyglutarylcarnitine, likely to be of maternal transfer.The multidisciplinary team, consisting of metabolic, dietetic and obstetric care providers, have responsibility to ensure the risk of acute decompensation in pregnant GA1 women is minimal.

Impairment of astrocytic glutaminolysis in glutaric aciduria type I

Glutaric aciduria type I is a rare, autosomal recessive, inherited defect of glutaryl-CoA dehydrogenase. Deficiency of this protein in L-lysine degradation leads to the characteristic accumulation of nontoxic glutarylcarnitine and neurotoxic glutaric acid (GA), glutaryl-CoA, and 3-hydroxyglutaric acid. Untreated patients develop bilateral lesions of basal ganglia resulting in a complex movement disorder with predominant dystonia in infancy and early childhood. The current pathomechanistic concept strongly focuses on imbalanced neuronal energy metabolism due to accumulating metabolites, whereas little is known about the pathomechanistic role of astrocytes, which are thought to be in constant metabolic crosstalk with neurons. We found that glutaric acid (GA) causes astrocytic cell death under starvation cell culture conditions, i.e. low glucose, without glutamine and fetal calf serum. Glutamine completely abolished GA-induced toxicity, suggesting involvement of glutaminolysis. Increasing dependence on glutaminolysis by chemical induction of hypoxia signaling-potentiated GA-induced toxicity. We further show that GA disturbs glutamine degradation by specifically inhibiting glutamate dehydrogenase. Summarizing our study shows that pathologically relevant concentrations of GA block an important step in the metabolic crosstalk between neurons and astrocytes, ultimately leading to astrocytic cell death.

Disease-causing mutations affecting surface residues of mitochondrial glutaryl-CoA dehydrogenase impair stability, heteromeric complex formation and mitochondria architecture

The neurometabolic disorder glutaric aciduria type 1 (GA1) is caused by mutations in the GCDH gene encoding the mitochondrial matrix protein glutaryl-CoA dehydrogenase (GCDH), which forms homo- and heteromeric complexes. Twenty percent of all pathogenic mutations affect single amino acid residues on the surface of GCDH resulting in a severe clinical phenotype. We report here on heterologous expression studies of 18 missense mutations identified in GA1 patients affecting surface amino acids. Western blot and pulse chase experiments revealed that the stability of half of the GCDH mutants was significantly reduced. In silico analyses showed that none of the mutations impaired the 3D structure of GCDH. Immunofluorescence co-localisation studies in HeLa cells demonstrated that all GCDH mutants were correctly translocated into mitochondria. Surprisingly, the expression of p.Arg88Cys GCDH as well as further substitutions by alanine, lysine, or methionine but not histidine or leucine resulted in the disruption of mitochondrial architecture forming longitudinal structures composed of stacks of cristae and partial loss of the outer mitochondrial membrane. The expression of mitochondrial fusion or fission proteins was not affected in these cells. Bioluminescence resonance energy transfer analyses revealed that all GCDH mutants exhibit an increased binding affinity to electron transfer flavoprotein beta, whereas only p.Tyr155His GCDH showed a reduced interaction with dihydrolipoamide succinyl transferase. Our data underscore the impact of GCDH protein interactions mediated by amino acid residues on the surface of GCDH required for proper enzymatic activity.

[Effect of glutaryl-CoA dehydrogenase gene silencing and high-concentration lysine on the viability of BRL hepatocytes]

OBJECTIVE

To investigate the effect of glutaryl-CoA dehydrogenase (GCDH) gene silencing and accumulation of lysine metabolites on the viability of hepatocytes.

METHODS

BRL cells were divided into normal control group, negative control group, and GCDH silencing group. The shRNA lentiviral vector for silencing GCDH gene was constructed, and the BRL hepatocytes in the GCDH silencing group and the negative control group were infected with this lentivirus and negative control virus respectively, and then cultured in a medium containing 5 mmol/L lysine. Immunofluorescence assay was used to measure the infection efficiency of lentivirus. Western blot was used to measure the expression of GCDH protein. MTT assay was used to evaluate cell viability. Hoechest33342 staining was used to measure cell apoptosis. Western blot was used to measure the expression of Caspase-3, an index of cell apoptosis.

RESULTS

The lentivirus constructed effectively silenced the GCDH gene in hepatocytes (P<0.01). MTT assay and Hoechest 33342 staining showed no significant differences in cell viability and apoptosis between groups (P>0.05). There was also no significant difference in the expression of Caspase-3 protein between groups (P>0.05).

CONCLUSIONS

GCDH gene silencing and accumulation of lysine metabolites may not cause marked hepatocyte injury.

Glutaric Aciduria Type 3: Three Unrelated Canadian Cases, with Different Routes of Ascertainment

Glutaric aciduria type 3 (GA3) is associated with decreased conversion of free glutaric acid to glutaryl-coA, reflecting deficiency of succinate-hydroxymethylglutarate coA-transferase, caused by variants in the SUGCT (C7orf10) gene. GA3 remains less well known, characterised and understood than glutaric aciduria types 1 and 2. It is generally considered a likely "non-disease," but this is based on limited supporting information, with only nine individuals with GA3 described in the literature. Clinicians encountering a patient with GA3 therefore still face a dilemma of whether or not this should be dismissed as irrelevant.We have identified three unrelated Canadian patients with GA3. Two came to clinical attention because of symptoms, while the third was identified by a population urine-based newborn screening programme and has so far remained asymptomatic. We describe the clinical histories, biochemical characterisation and genotypes of these individuals. Examination of allele frequencies underlines the fact that GA3 is underdiagnosed. While one probable factor is that some GA3 patients remain asymptomatic, we highlight other plausible reasons whereby this diagnosis might be overlooked.Gastrointestinal disturbances were previously reported in some GA3 patients. In one of our patients, severe episodes of cyclic vomiting were the major problem. A trial of antibiotic treatment, to minimise bacterial GA production, was followed by significant clinical improvement.At present, there is insufficient evidence to define any specific clinical phenotype as attributable to GA3. However, we consider that it would be premature to assume that this condition is completely benign in all individuals at all times.

Glutaric Aciduria Type 1 and Acute Renal Failure: Case Report and Suggested Pathomechanisms

Glutaric aciduria type 1 (GA1) is caused by deficiency of the mitochondrial matrix enzyme glutaryl-CoA dehydrogenase (GCDH), leading to accumulation of glutaric acid (GA) and 3-hydroxyglutaric acid (3OHGA) in tissues and body fluids. During catabolic crises, GA1 patients are prone to the development of striatal necrosis and a subsequent irreversible movement disorder during a time window of vulnerability in early infancy. Thus, GA1 had been considered a pure "cerebral organic aciduria" in the past. Single case reports have indicated the occurrence of acute renal dysfunction in children affected by GA1. In addition, growing evidence arises that GA1 patients may develop chronic renal failure during adulthood independent of the previous occurrence of encephalopathic crises. The underlying mechanisms are yet unknown. Here we report on a 3-year-old GA1 patient who died following the development of acute renal failure most likely due to haemolytic uraemic syndrome associated with a pneumococcal infection. We hypothesise that known GA1 pathomechanisms, namely the endothelial dysfunction mediated by 3OHGA, as well as the transporter mechanisms for the urinary excretion of GA and 3OHGA, are involved in the development of glomerular and tubular dysfunction, respectively, and may contribute to a pre-disposition of GA1 patients to renal disease. We recommend careful differential monitoring of glomerular and tubular renal function in GA1 patients.

Extrastriatal changes in patients with late-onset glutaric aciduria type I highlight the risk of long-term neurotoxicity

BACKGROUND

Without neonatal initiation of treatment, 80-90% of patients with glutaric aciduria type 1 (GA1) develop striatal injury during the first six years of life resulting in a complex, predominantly dystonic movement disorder. Onset of motor symptoms may be acute following encephalopathic crisis or insidious without apparent crisis. Additionally, so-called late-onset GA1 has been described in single patients diagnosed after the age of 6 years. With the aim of better characterizing and understanding late-onset GA1 we analyzed clinical findings, biochemical phenotype, and MRI changes of eight late-onset patients and compared these to eight control patients over the age of 6 years with early diagnosis and start of treatment.

RESULTS

No late-onset or control patient had either dystonia or striatal lesions on MRI. All late-onset (8/8) patients were high excretors, but only four of eight control patients. Two of eight late-onset patients were diagnosed after the age of 60 years, presenting with dementia, tremor, and epilepsy, while six were diagnosed before the age of 30 years: Three were asymptomatic mothers identified by following a positive screening result in their newborns and three had non-specific general symptoms, one with additional mild neurological deficits. Frontotemporal hypoplasia and white matter changes were present in all eight and subependymal lesions in six late-onset patients. At comparable age a greater proportion of late-onset patients had (non-specific) clinical symptoms and possibly subependymal nodules compared to control patients, in particular in comparison to the four clinically and MR-wise asymptomatic low-excreting control patients.

CONCLUSIONS

While clinical findings are non-specific, frontotemporal hypoplasia and subependymal nodules are characteristic MRI findings of late-onset GA1 and should trigger diagnostic investigation for this rare disease. Apart from their apparent non-susceptibility for striatal injury despite lack of treatment, patients with late-onset GA1 are not categorically different from early treated control patients. Differences between late-onset patients and early treated control patients most likely reflect greater cumulative neurotoxicity in individuals remaining undiagnosed and untreated for years, even decades as well as the higher long-term risk of high excretors for intracerebral accumulation of neurotoxic metabolites compared to low excretors.

Glutaric Acidemia Type 1: A Case of Infantile Stroke

BACKGROUND

Glutaric acidemia Type 1 (GA-1) is an autosomal recessively inherited metabolic disorder which is associated with GCDH gene mutations which alters the glutaryl-CoA dehydrogenase, an enzyme playing role in the catabolic pathways of the amino acids lysine, hydroxylysine, and tryptophan. Clinical findings are often encephalopathic crises, dystonia, and extrapyramidal symptoms.

CASE REPORT

A 9-month-old male infant referred to our department with focal tonic-clonic seizures during rotavirus infection and acute infarcts in MRI. Clinical manifestation, MRI findings, and metabolic investigations directed thoughts towards GA-I. Molecular genetic testing revealed a homozygous c.572T>C (p.M191T) mutation in GCDH gene which confirmed the diagnosis. Application of protein restricted diet, carnitine and riboflavin supplementations prevented the progression of Magnetic Resonance Imaging (MRI) and clinical pathologic findings during the 1 year of follow-up period.

CONCLUSION

This case is of great importance since it shows possibility of infantile stroke in GA-1, significance of early diagnosis and phenotypic variability of disease.