The behavioral phenotype of children and adolescents with attenuated non-ketotic hyperglycinemia, intermediate to good subtype.

AIM: We aim to describe the behavioral phenotype of children and adolescents with the good to intermediate attenuated form of non-ketotic hyperglycinemia (NKH) and to explore associations between the behavioral phenotype and age, sex, plasma glycine levels and drug treatment. METHOD: Parents of children with attenuated NKH completed questionnaires assessing maladaptive behavior, adaptive behavior, social communication, speech/language development and motor development in addition to demographic and medical questions. RESULTS AND INTERPRETATION: Twelve children, age 6 to 21y, functioned at mild to severe intellectual disability levels. Their speech/language development was in line with their developmental quotient. Relative to their intellectual functioning, their motor development and communication were weaker in comparison to their general development. Their adaptive behavior, however, appeared a relative strength. There was no evidence for autism spectrum disorder occurring more frequently than expected, rather social skills, except for communication, were rated as a relative strength. Maladaptive behaviors with ADHD-like characteristics were present in more than two thirds of children. Maladaptive behaviors were significantly related to female sex and to taking dextromethorphan, but no significant relation between plasma glycine levels and behavior was found. Future studies will need to evaluate causality in the observed relation between dextromethorphan use and maladaptive behaviors. Clinicians should reconsider the benefit of dextromethorphan when presented with disruptive behaviors in children with attenuated NKH.

Metabolic Rewiring and Altered Glial Differentiation in an iPSC-Derived Astrocyte Model Derived from a Nonketotic Hyperglycinemia Patient.

The pathophysiology of nonketotic hyperglycinemia (NKH), a rare neuro-metabolic disorder associated with severe brain malformations and life-threatening neurological manifestations, remains incompletely understood. Therefore, a valid human neural model is essential. We aimed to investigate the impact of GLDC gene variants, which cause NKH, on cellular fitness during the differentiation process of human induced pluripotent stem cells (iPSCs) into iPSC-derived astrocytes and to identify sustainable mechanisms capable of overcoming GLDC deficiency. We developed the GLDC27-FiPS4F-1 line and performed metabolomic, mRNA abundance, and protein analyses. This study showed that although GLDC27-FiPS4F-1 maintained the parental genetic profile, it underwent a metabolic switch to an altered serine-glycine-one-carbon metabolism with a coordinated cell growth and cell cycle proliferation response. We then differentiated the iPSCs into neural progenitor cells (NPCs) and astrocyte-lineage cells. Our analysis showed that GLDC-deficient NPCs had shifted towards a more heterogeneous astrocyte lineage with increased expression of the radial glial markers GFAP and GLAST and the neuronal markers MAP2 and NeuN. In addition, we detected changes in other genes related to serine and glycine metabolism and transport, all consistent with the need to maintain glycine at physiological levels. These findings improve our understanding of the pathology of nonketotic hyperglycinemia and offer new perspectives for therapeutic options.

Non-Ketotic Hyperglycinemia: A Rare Presentation with Neurological and Skeletal Abnormalities.

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Teaching NeuroImage: Glutaredoxin-5-Associated Variant Nonketotic Hyperglycinemia.

A 5-year-old boy presented with subacute motor regression since age 2.5 years. Examination revealed spasticity of bilateral lower extremities, generalized dystonia, and pseudobulbar palsy. Investigations revealed raised plasma lactate (2.5 mmol/L, normal range 0.8-1.5 mmol/L) and no evidence of sideroblastic anemia. Neuroimaging showed cavitating leukoencephalopathy with involvement of long tracts (corticospinal, spinothalamic tracts) and dorsolateral columns of cervicothoracic cord (Figures 1 and 2). A next-generation sequencing test identified a novel homozygous missense variant (c.171C > A, p.Phe57Leu) in exon 1 of the Glutaredoxin-5 (GLRX5) gene.

Pathogenic variants in GCSH encoding the moonlighting H-protein cause combined nonketotic hyperglycinemia and lipoate deficiency.

Maintaining protein lipoylation is vital for cell metabolism. The H-protein encoded by GCSH has a dual role in protein lipoylation required for bioenergetic enzymes including pyruvate dehydrogenase and 2-ketoglutarate dehydrogenase, and in the one-carbon metabolism through its involvement in glycine cleavage enzyme system, intersecting two vital roles for cell survival. Here, we report six patients with biallelic pathogenic variants in GCSH and a broad clinical spectrum ranging from neonatal fatal glycine encephalopathy to an attenuated phenotype of developmental delay, behavioral problems, limited epilepsy and variable movement problems. The mutational spectrum includes one insertion c.293-2_293-1insT, one deletion c.122_(228 + 1_229-1) del, one duplication of exons 4 and 5, one nonsense variant p.Gln76*and four missense p.His57Arg, p.Pro115Leu and p.Thr148Pro and the previously described p.Met1?. Via functional studies in patient's fibroblasts, molecular modeling, expression analysis in GCSH knockdown COS7 cells and yeast, and in vitro protein studies, we demonstrate for the first time that most variants identified in our cohort produced a hypomorphic effect on both mitochondrial activities, protein lipoylation and glycine metabolism, causing combined deficiency, whereas some missense variants affect primarily one function only. The clinical features of the patients reflect the impact of the GCSH changes on any of the two functions analyzed. Our analysis illustrates the complex interplay of functional and clinical impact when pathogenic variants affect a multifunctional protein involved in two metabolic pathways and emphasizes the value of the functional assays to select the treatment and investigate new personalized options.

Ketogenic diet as a glycine lowering therapy in nonketotic hyperglycinemia and impact on brain glycine levels.

BACKGROUND: Nonketotic hyperglycinemia (NKH) is a severe neurometabolic disorder characterized by increased glycine levels. Current glycine reduction therapy uses high doses of sodium benzoate. The ketogenic diet (KD) may represent an alternative method of glycine reduction. AIM: We aimed to assess clinical and biochemical effects of two glycine reduction strategies: high dose benzoate versus KD with low dose benzoate. METHODS: Six infants with NKH were first treated with high dose benzoate therapy to achieve target plasma glycine levels, and then switched to KD with low dose benzoate. They were evaluated as clinically indicated by physical examination, electroencephalogram, plasma and cerebral spinal fluid amino acid levels. Brain glycine levels were monitored by magnetic resonance spectroscopy (MRS). RESULTS: Average plasma glycine levels were significantly lower with KD compared to benzoate monotherapy by on average 28%. Two infants underwent comparative assessments of brain glycine levels via serial MRS. A 30% reduction of brain glycine levels was observed in the basal ganglia and a 50% reduction in the white matter, which remained elevated above normal, and was equivalent between the KD and high dose benzoate therapies. CSF analysis obtained while participants remained on the KD showed a decrease in glycine, serine and threonine levels, reflecting their gluconeogenetic usage. Clinically, half the patients had seizure reduction on KD, otherwise the clinical impact was variable. CONCLUSION: KD is an effective glycine reduction method in NKH, and may provide a more consistent reduction in plasma glycine levels than high-dose benzoate therapy. Both high-dose benzoate therapy and KD equally reduced but did not normalize brain glycine levels even in the setting of low-normal plasma glycine.

Integrative Approach to Predict Severity in Nonketotic Hyperglycinemia.

OBJECTIVE: Glycine encephalopathy, also known as nonketotic hyperglycinemia (NKH), is an inherited neurometabolic disorder with variable clinical course and severity, ranging from infantile epileptic encephalopathy to psychiatric disorders. A precise phenotypic characterization and an evaluation of predictive approaches are needed. METHODS: Longitudinal clinical and biochemical data of 25 individuals with NKH from the patient registry of the International Working Group on Neurotransmitter Related Disorders were studied with in silico analyses, pathogenicity scores, and molecular modeling of GLDC and AMT variants. RESULTS: Symptom onset (p < 0.01) and diagnosis occur earlier in life in severe NKH (p < 0.01). Presenting symptoms affect the age at diagnosis. Psychiatric problems occur predominantly in attenuated NKH. Onset age ≥ 3 months (66% specificity, 100% sensitivity, area under the curve [AUC] = 0.87) and cerebrospinal fluid (CSF)/plasma glycine ratio ≤ 0.09 (57% specificity, 100% sensitivity, AUC = 0.88) are sensitive indicators for attenuated NKH, whereas CSF glycine concentration ≥ 116.5µmol/l (100% specificity, 93% sensitivity, AUC = 0.97) and CSF/plasma glycine ratio ≥ 0.15 (100% specificity, 64% sensitivity, AUC = 0.88) are specific for severe forms. A ratio threshold of 0.128 discriminates the overlapping range. We present 10 new GLDC variants. Two mild variants resulted in attenuated, whereas 2 severe variants or 1 mild and 1 severe variant led to severe phenotype. Based on clinical, biochemical, and genetic parameters, we propose a severity prediction model. INTERPRETATION: This study widens the phenotypic spectrum of attenuated NKH and expands the number of pathogenic variants. The multiparametric approach provides a promising tool to predict disease severity, helping to improve clinical management strategies. ANN NEUROL 2022;92:292-303.

Cerebrospinal fluid amino acids glycine, serine, and threonine in nonketotic hyperglycinemia.

Nonketotic hyperglycinemia (NKH) is caused by deficient glycine cleavage enzyme activity and characterized by elevated brain glycine. Metabolism of glycine is connected enzymatically to serine through serine hydroxymethyltransferase and shares transporters with serine and threonine. We aimed to evaluate changes in serine and threonine in NKH patients, and relate this to clinical outcome severity. Age-related reference values were developed for cerebrospinal fluid (CSF) serine and threonine from 274 controls, and in a cross-sectional study compared to 61 genetically proven NKH patients, categorized according to outcome. CSF d-serine and l-serine levels were stereoselectively determined in seven NKH patients and compared to 29 age-matched controls. In addition to elevated CSF glycine, NKH patients had significantly decreased levels of CSF serine and increased levels of CSF threonine, even after age-adjustment. The CSF serine/threonine ratio discriminated between NKH patients and controls. The CSF glycine/serine aided in discrimination between severe and attenuated neonates with NKH. Over all ages, the CSF glycine, serine and threonine had moderate to fair correlation with outcome classes. After age-adjustment, only the CSF glycine level provided good discrimination between outcome classes. In untreated patients, d-serine was more reduced than l-serine, with a decreased d/l-serine ratio, indicating a specific impact on d-serine metabolism. We conclude that in NKH the elevation of glycine is accompanied by changes in l-serine, d-serine and threonine, likely reflecting a perturbation of the serine shuttle and metabolism, and of one-carbon metabolism. This provides additional guidance on diagnosis and prognosis, and opens new therapeutic avenues to be explored.

Manejo anestésico y perioperatorio en paciente pediátrico con hiperglicinemia no cetósica / Anesthetic and perioperative management in children with non-ketotic hyperglycinemiawith non-ketotic hyperglycinemia

Presentación del caso: se reporta un paciente pediátrico con diagnóstico de hiperglicinemia no cetósica (HNC), enfermedad neurometabólica poco frecuente ocasionada por una deficiencia en el sistema de segmentación de la glicina, codificada por los genes GLDC, GCSH, AMT y GCSL que conduce a niveles elevados de glicina en la sinapsis generando un efecto agonista prolongado en los receptores N-metil-D-aspartato (NMDA). Discusión y conclusiones: se asocia con hipotonía, convulsiones y trastornos de la deglución, los cuales dependerán de la edad de presentación. Se revisa la literatura actual para el abordaje perioperatorio.

Case presentation: we report a child with a diagnosis of non-ketotic hyperglycinemia (NKGH), a rare neurometabolic disease caused by a defect in the glycine cleavage system, encoded by the GLDC, GCSH, AMT and GCSL genes resulting in elevated synaptic glycine levels generating a prolonged agonist effect on N-methyl-D-aspartate (NMDA) receptors. Discussion and conclusions: it is associated with hypotonia, seizures and swallowing disorders, which will depend on the age at presentation. A literature review was conducted to tailor perioperative approach.

Genotypic and phenotypic features in Turkish patients with classic nonketotic hyperglycinemia.

Nonketotic hyperglycinemia is an autosomal recessive inborn error of glycine metabolism, characterized by deficient activity of the glycine cleavage enzyme system. Classic nonketotic hyperglycinemia is caused by mutations or genomic changes in genes that encode the protein components of the glycine cleavage enzyme system. We aimed to investigate clinical, biochemical, radiological findings and molecular genetic data in ten Turkish patients with classic nonketotic hyperglycinemia. Ten Turkish patients who were diagnosed with classic nonketotic hyperglycinemia in a single center from 2013 to 2019 were included in this study. Their clinical, radiological, electrophysiological and laboratory data were collected retrospectively. Sixty percent of the patients were in neonatal group, while 40 % of the patients were infantile. There were no late-onset patients. 90 % of the patients had the severe form. All patients had developmental delay and seizures. Mortality ratio was 30 % in all groups and 50 % in the neonatal group, while no mortality was seen in infantile group. Median (range) values of cerebrospinal fluid (CSF) glycine levels, plasma glycine levels and CSF/plasma glycine ratios were 148 (15-320) µmol/L, 896 (87-1910) µmol/L, 0.17 (0.09-0.21) respectively. Diffuse hypomyelination and corpus callosum anomaly were the most common cranial MRI findings and multifocal epileptic activity and burst supression pattern were the most common electroencephalographic findings. Six patients had variants in GLDC gene and four in AMT gene; five novel variants including AMT gene deletion were detected. Prognosis was poor and treatment was not effective, especially in the severe form. Classic nonketotic hyperglycinemia causes high morbidity and mortality. Neonatal-onset disease was more common and severe than infantile-onset disease. The ratio of AMT gene variants might be higher in Turkey than other countries. AMT gene deletion also plays a role in the etiology of classic nonketotic hyperglycinemia.

Biallelic start loss variant, c.1A > G in GCSH is associated with variant nonketotic hyperglycinemia.

The glycine cleavage system H protein (GCSH) is an integral part of the glycine cleavage system with its additional involvement in the synthesis and transport of lipoic acid. We hypothesize that pathogenic variants in GCSH can cause variant nonketotic hyperglycinemia (NKH), a heterogeneous group of disorders with findings resembling a combination of severe NKH (elevated levels of glycine in plasma and CSF, progressive lethargy, seizures, severe hypotonia, no developmental progress, early death) and mitochondriopathies (lactic acidosis, leukoencephalopathy and Leigh-like lesions on MRI). We herein report three individuals from two unrelated Indian families with clinical, biochemical, and radiological findings of variant NKH, harboring a biallelic start loss variant, c.1A > G in GCSH.

Genomic analyses of glycine decarboxylase neurogenic mutations yield a large-scale prediction model for prenatal disease.

Hundreds of mutations in a single gene result in rare diseases, but why mutations induce severe or attenuated states remains poorly understood. Defect in glycine decarboxylase (GLDC) causes Non-ketotic Hyperglycinemia (NKH), a neurological disease associated with elevation of plasma glycine. We unified a human multiparametric NKH mutation scale that separates severe from attenuated neurological disease with new in silico tools for murine and human genome level-analyses, gathered in vivo evidence from mice engineered with top-ranking attenuated and a highly pathogenic mutation, and integrated the data in a model of pre- and post-natal disease outcomes, relevant for over a hundred major and minor neurogenic mutations. Our findings suggest that highly severe neurogenic mutations predict fatal, prenatal disease that can be remedied by metabolic supplementation of dams, without amelioration of persistent plasma glycine. The work also provides a systems approach to identify functional consequences of mutations across hundreds of genetic diseases. Our studies provide a new framework for a large scale understanding of mutation functions and the prediction that severity of a neurogenic mutation is a direct measure of pre-natal disease in neurometabolic NKH mouse models. This framework can be extended to analyses of hundreds of monogenetic rare disorders where the underlying genes are known but understanding of the vast majority of mutations and why and how they cause disease, has yet to be realized.

Elevated preoptic brain activity in zebrafish glial glycine transporter mutants is linked to lethargy-like behaviors and delayed emergence from anesthesia.

Delayed emergence from anesthesia was previously reported in a case study of a child with Glycine Encephalopathy. To investigate the neural basis of this delayed emergence, we developed a zebrafish glial glycine transporter (glyt1 - / -) mutant model. We compared locomotor behaviors; dose-response curves for tricaine, ketamine, and 2,6-diisopropylphenol (propofol); time to emergence from these anesthetics; and time to emergence from propofol after craniotomy in glyt1-/- mutants and their siblings. To identify differentially active brain regions in glyt1-/- mutants, we used pERK immunohistochemistry as a proxy for brain-wide neuronal activity. We show that glyt1-/- mutants initiated normal bouts of movement less frequently indicating lethargy-like behaviors. Despite similar anesthesia dose-response curves, glyt1-/- mutants took over twice as long as their siblings to emerge from ketamine or propofol, mimicking findings from the human case study. Reducing glycine levels rescued timely emergence in glyt1-/- mutants, pointing to a causal role for elevated glycine. Brain-wide pERK staining showed elevated activity in hypnotic brain regions in glyt1-/- mutants under baseline conditions and a delay in sensorimotor integration during emergence from anesthesia. Our study links elevated activity in preoptic brain regions and reduced sensorimotor integration to lethargy-like behaviors and delayed emergence from propofol in glyt1-/- mutants.

GLYT1 encephalopathy: Further delineation of disease phenotype and discussion of pathophysiological mechanisms.

GLYT1 encephalopathy is a form of glycine encephalopathy caused by disturbance of glycine transport. The phenotypic spectrum of the disease has not yet been completely described, as only four unrelated families with the disorder have been reported to date. Common features of affected patients include neonatal hypotonia, respiratory failure, encephalopathy, myoclonic jerks, dysmorphic features, and musculoeskeletal anomalies. All reported affected patients harbor biallelic genetic variants in SLC6A9. SNP array together with Sanger sequencing were performed in a newborn with arthrogryposis and severe neurological impairment. The novel genetic variant c.997delC in SLC6A9 was detected in homozygous state in the patient. At protein level, the predicted change is p.(Arg333Alafs*3), which most probably results in a loss of protein function. The variant cosegregated with the disease in the family. A subsequent pregnancy with ultrasound anomalies was also affected. The proband presented the core phenotypic features of GLYT1 encephalopathy, but also a burst suppression pattern on the electroencephalogram, a clinical feature not previously associated with the disorder. Our results suggest that the appearance of this pattern correlates with higher cerebrospinal fluid glycine levels and cerebrospinal fluid/plasma glycine ratios. A detailed discussion on the possible pathophysiological mechanisms of the disorder is also provided.

Hiperglicinemia no cetósica neonatal, fenotipo atenuado / Neonatal nonketotic hyperglycinemia, attenuated phenotype / Hiperglicinemia não-cetótica neonatal, fenótipo atenuado

Introducción. La Hiperglicinemia no Cetósica (HNC) es un error innato del metabolismo de herencia autosómica recesiva, cuya principal característica es la acumulación de glicina en los fluidos corporales, producido por una falla en el complejo de clivaje enzimático de este aminoácido. Presentación del caso. Presentamos el caso de un recién nacido de 36 semanas, con adaptación neonatal espontánea, sin historia de noxa perinatal ni hipoglicemia documentada, quien tras un corto período de 24 horas presentó deterioro neurológico progresivo, rápida alteración del estado de conciencia hasta el coma y falla ventilatoria. Llamó la atención al ingreso la hipotonía severa generalizada, hiporreflexia, ausencia de reflejos primitivos, con episodios de hipo aislado y movimientos oculares anormales. Ante la sospecha de un error innato del metabolismo se realizó el perfil de aminoácidos donde se evidenció elevación significativa de la glicina, 1417 mmol/L (referencia 94-553 umol/L). Se solicitaron aminoácidos en líquido cefalorraquídeo, glicina muy elevada 1263 mmol/L (referencia 3-7 umol/L), con lo que se confirma la sospecha de hiperglicinemia no cetósica. Se decidió iniciar manejo con benzoato de sodio y dextrometorfano. La resonancia magnética inicial fue normal, en estudio control se encontraron al igual que en el electroencefalograma hallazgos reportados previamente en la literatura para esta patología. Discusión. La mayoría de los niños con HNC se presentan en el período neonatal o en la primera infancia, y solo los casos más leves se presentan al final de la infancia o la niñez. En las presentaciones de inicio neonatal, el 85% tiene HNC grave y el 15% tiene forma atenuada, como este caso. El diagnóstico de la HNC se hace con base en la sospecha clínica, confirmada por los hallazgos de laboratorio, con la alteración característica de la glicina tanto en plasma como en el LCR y soportada por los hallazgos de las neuroimágenes y electroencefalograma (EEG). Conclusiones. La HNC no es una condición tan inusual, aunque sí posiblemente subdiagnosticada por la forma de presentación tan catastrófica, además porque no produce grandes desarreglos metabólicos de rápido diagnóstico. Por este motivo, ante un paciente con cuadro clínico sugestivo, con coma, alteración respiratoria y convulsiones de difícil manejo, y muy característicamente hipo, debe solicitarse el estudio de aminoácidos en plasma, neuroimágenes y EEG, con el fin de instaurar un manejo temprano.

Introduction. Nonketotic hyperglycinemia (NKH) is an autosomal recessive innate error of metabolism, whose main characteristic is the accumulation of glycine in body fluids, produced by a failure in the enzymatic cleavage complex of this amino acid. Case Presentation. We present the case of a 36-week-old newborn, with spontaneous neonatal adaptation, no history of perinatal noxa or documented hypoglycemia, who after a short period of 24 hours presented progressive neurological deterioration, rapid alteration of consciousness to coma and ventilatory failure. At admission the patient was noted for severe generalized hypotonia, hyporeflexia, absence of primitive reflexes, with episodes of isolated hiccups and abnormal eye movements. In view of the suspicion of an innate error of metabolism, an amino acid profile was performed, showing a significant elevation of glycine, 1417 umol/L (reference 94-553 umol/L). Amino acids were requested in cerebrospinal fluid, glycine very elevated 1263 umol/L (reference 3-7 umol/L), confirming the suspicion of nonketotic hyperglycinemia. It was decided to start treatment with sodium benzoate and dextromethorphan. The initial MRI was normal; in the control study, findings previously reported in the literature for this pathology were found, as well as in the electroencephalogram. Discussion. Most children with NKH will display it in the neonatal period or early infancy, with only the mildest cases presenting in late infancy or childhood. In neonatal-onset cases, 85% have severe NKH and 15% have attenuated form, as in this case. The diagnosis of NKH is made based on clinical suspicion, confirmed by laboratory findings, with the characteristic alteration of glycine in both plasma and CSF and supported by neuroimaging and electroencephalogram (EEG) findings. Conclusions. NKH is not such an unusual condition, although it is possibly underdiagnosed because of its catastrophic presentation and because it does not produce major metabolic disorders that are quickly diagnosed. For this reason, in a patient with a suggestive clinical condition, with coma, respiratory alteration and unmanageable seizures, and very characteristically hiccups, the study of amino acids in plasma, neuroimaging and EEG should be requested, in order to establish early treatment.

Introdução. A hiperglicinemia não-cetótica (HNC) é um erro inato do metabolismo de herança autossômica recessiva, cuja principal característica é o acúmulo de glicina nos fluidos corporais, produzido por uma falha no complexo de clivagem enzimática deste aminoácido. Apresentação do caso. Apresentamos o caso de um recém-nascido de 36 semanas, com adaptação neonatal espontânea, sem história de noxa perinatal nem hipoglicemia documentada, que após um curto período de 24 horas apresentou deterioração neurológica progressiva, alteração rápida de consciência até coma e falha ventilatória. Na admissão, eram notáveis a hipotonia grave generalizada, hiporreflexia, ausência de reflexos primitivos, com episódios de soluços isolados e movimentos oculares anormais. Diante da suspeita de erro inato no metabolismo, foi realizado o perfil de aminoácidos, onde foi constatada elevação significativa da glicina, 1417umol/L (referência 94-553 umol/L). Foram solicitados aminoácidos no líquido cefalorraquidiano, glicina muito alta 1263umol/L (referência 3-7 umol/L), confirmando a suspeita de hiperglicinemia não-cetótica. Foi decidido iniciar o tratamento com benzoato de sódio e dextrometorfano. A ressonância magnética inicial foi normal, tanto em estudo controle quanto no eletroencefalograma, foram encontrados achados previamente relatados na literatura para esta patologia. Discussão. A maioria das crianças com HNC estão no período neonatal ou na primeira infância, e apenas os casos mais leves ocorrem na infância ou na infância tardia. Nas apresentações de início neonatal, 85% têm HNC grave e 15% têm forma atenuada, como neste caso. O diagnóstico de HNC é feito com base na suspeita clínica, confirmada por achados laboratoriais, com alteração característica da glicina tanto no plasma quanto no LCR e apoiado por achados de neuroimagem e eletroencefalograma (EEG). Conclusões. A HNC não é uma condição tão incomum, embora possivelmente seja subdiagnosticada por sua apresentação catastrófica, também por não produzir grandes distúrbios metabólicos que possam ser diagnosticados rapidamente. Por esse motivo, em um paciente com quadro clínico sugestivo, com coma, distúrbios respiratórios e convulsões de difícil manejo, e soluços muito característicos, deve ser solicitado um estudo de aminoácidos no plasma, neuroimagem e EEG a fim de estabelecer um tratamento rápido.