Glutamic-oxaloacetic transaminase (GOT), also known as aspartate aminotransferase, catalyzes the reversible transamination of oxaloacetate and glutamate to aspartate and α-ketoglutarate. Two isoforms, cytosolic (GOT1) and mitochondrial (GOT2), are integral to the malate-aspartate shuttle, a key regulator of intracellular redox homeostasis. Recently, 5 patients with biallelic variants in GOT2 were described, presenting with developmental and epileptic encephalopathy. We report 11 additional patients with homozygous GOT2 variants, along with additional data from 4 previously reported patients. Through genetic, clinical, and biochemical analyses, we further characterize the phenotypic spectrum of GOT2 deficiency. Most patients exhibited progressive neurodevelopmental delay, severe to profound intellectual disability, infantile epilepsy, progressive microcephaly, and hypotonia evolving into spasticity with axial hypotonia. Dysmorphic features included narrow foreheads, broad nasal tips, and tall or pointed chins. Neuroimaging revealed 2 severity groups based on cerebral volume loss and myelination defects. Thinning of the corpus callosum and white matter abnormalities were common. Biochemical profiling identified low aspartate and high glycerol-3-phosphate in dried blood spots as potential screening markers. Patient fibroblast cells showed reduced serine and glycine biosynthesis, rescuable by pyruvate supplementation. These findings expand the phenotypic spectrum of GOT2 deficiency, establish it as a cause of developmental epileptic encephalopathy, and propose novel biomarkers for diagnosis and treatment.

Lipoyl transferase 2 is involved in the biosynthesis of lipoate. Lipoate is the cofactor for the glycine cleavage system and four dehydrogenase enzymes. Biallelic variants in LIPT2 causing severe neonatal encephalopathy was first described in 2017. Clinical data were collected by retrospective chart review after obtaining consent from parents. The pathogenicity of these variants was further delineated using a yeast model. The YEp352-LIPT2 plasmid was used as a template to generate the two patient variants using QuickChange Lightning Site-Directed Mutagenesis Kit. The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties. Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia. Patient had elevations in lactate (6.1 mmol/L) and glycine. Exome sequencing showed two variants of uncertain significance in trans in the LIPT2 gene: c.346 G>T and c.418C>T. Patient was started on lipoic acid, thiamine, and COQ10. Yeast complementation experiments indicate that both patient mutant variants result in diminished function versions of the LIPT2 protein. We report the fourth case of LIPT2-related disorder. Proband shared significant overlap with previous patients; however, there was a distinct movement disorder and brain malformations, which have not been previously described. Unlike most neurometabolic disorders where dystonia develops later after metabolic stroke in basal ganglia, LIPT2-related disorder seems unique due to early onset of dystonia due to energy deficit in the developing brain. Lipoic acid supplementation has not led to significant clinical improvement. Analyses in yeast indicate that novel variants are deleterious but have retained some functionality.

Nonketotic hyperglycinemia (NKH) is a rare autosomal recessive disorder caused by defects in the glycine cleavage system. Most patients with early-onset NKH present with severe manifestations, including poor neurological outcomes and refractory seizures. However, a proportion of neonatally presenting patients exhibit the attenuated phenotype, characterized by variable clinical features. We report a boy with infantile-onset NKH who achieved long-term seizure remission into adolescence. A three-month-old boy developed infantile spasms refractory to standard antiepileptic drugs and worsened by valproic acid. Laboratory findings revealed elevated glycine levels in plasma and cerebrospinal fluid with an increased CSF/plasma ratio of glycine. A glycine breath test indicated partial reduction of glycine metabolism. He was diagnosed with early-onset NKH at nine months, and thereafter, specific treatments were started with sodium benzoate and dextromethorphan. He exhibited severe developmental delay under sustained seizure control. Genetic testing at 11 years of age revealed compound heterozygous variants in the AMT gene: a novel missense variant (p.L116R) and a pathogenic frameshift variant (p.P20fs*76). At 15 years, he presented with tremor as rhythmic limb shaking and lethargy with abnormal 5 Hz waves in the electroencephalogram during influenza A, whereas any epileptic seizures did not occur. No suggestive findings of encephalitis were observed on brain MRI or CSF analysis, but steroid pulse therapy was administered along with baseline NKH therapy. No seizures occurred, and neurological findings seemed unaffected by this episode. This case illustrates that attenuated NKH can be well managed with sustained seizure-free status into adolescence, even in and after subclinical influenza encephalopathy, suggesting potential prophylactic effects of sodium benzoate and dextromethorphan.

Nonketotic hyperglycinaemia (NKH) is an autosomal recessive neurometabolic disorder resulting from deficient glycine cleavage system activity, causing severe neurological impairment. While NKH is typically associated with pathogenic variants in glycine decarboxylase (GLDC) or aminomethyltransferase, the role of synonymous variants remains uncertain. To date, no cases of NKH caused by GLDC homozygous synonymous variants have been reported. Herein, a female infant born to consanguineous parents who developed refractory seizures, progressing to infantile epileptic spasms syndrome at 2 months is reported. Initial genetic testing identified a homozygous synonymous GLDC variant (c.1023G > A, p.Val341=), previously classified as "likely benign" in ClinVar (variation identification number: 1108119). Minigene splicing analysis revealed that the c.1023G > A variant caused a 38-base pair deletion in exon 7 (r.1021_1058del), Given the phenotypic characteristics of the child, we predict that this may resulting in a frameshift mutation (p.Val341ArgfsTer56) and a truncated protein. This functional evidence confirmed the pathogenicity of the variant.

Nonketotic hyperglycinemia (NKH) is a rare, life-threatening genetic disorder. The patients usually show heterogeneous and nonspecific symptoms, resulting in diagnosis challenges using conventional approaches. Here, the clinical presentation and genetic features of 20 Chinese patients were examined and reported in order to clarify the natural history and prognosis of NKH in China. The Human Gene Mutation Database and literature regarding NKH in China were reviewed. Age of onset, clinical characteristics, genetic analysis, cranial magnetic resonance imaging (MRI) and electroencephalography (EEG) examinations, and outcome of the patients were analyzed. Natural history experiences and follow-up assays for five patients who were followed in our center were described. Among all 20 NKH patients, 17 (85%) had the neonatal type and 3 (15%) had the infantile type, no late-onset cases were detected. Patients showed up for admission with a history of seizures (15/20), lethargy (14/20), hypotonia (11/20), apnea (9/20), and feeble sobbing (4/20). Brain MRI findings included abnormal signals in the internal capsule, cerebellum, or brainstem (6/14), dysplasia of the corpus callosum (5/14), and white matter abnormalities (3/14). EEG evaluations showed anomalies such as burst suppression (4/8) and hypsarrhythmia and/or epileptic activity (6/8). Median values of cerebrospinal fluid (CSF) glycine levels, plasma glycine levels and CSF/plasma glycine ratios were135.2 (range, 6.3-546.3) μmol/L, 998.2 (range,75-3,084) μmol/L, 0.16 (range, 0.03-0.60) respectively. Genetic analyses revealed four new variations and GLDC, AMT gene abnormalities in 13 (65%), 7 (35%) case, respectively. Prognosis information was available for 18 cases: nine patients died, eight in the neonatal period. Among the nine survivors, varying developmental disorders were observed. Different disease processes and outcomes were found in Chinese NKH patients, according to this study. The initial clinical presentations, CSF glycine levels and CSF to plasma glycine ratios do not reliably predict prognosis, while MRI and EEG abnormalities may indicate a poor outlook. NKH diagnosis should be considered for neonates presenting specific symptoms. The present survey provides clinical data that support the development of a standardized protocol for diagnosing and treating NKH in China.