Developmental and epileptic encephalopathy 82 (DEE82) with novel compound heterozygous mutations of GOT2 gene

PURPOSE

Developmental and Epileptic Encephalopathies (DEEs) are rare neurological disorders characterized by early-onset medically resistant epileptic seizures, structural brain malformations, and severe developmental delays. These disorders can arise from mutations in genes involved in vital metabolic pathways, including those within the brain. Recent studies have implicated defects in the mitochondrial malate aspartate shuttle (MAS) as potential contributors to the clinical manifestation of infantile epileptic encephalopathy. Although rare, mutations in MDH1, MDH2, AGC1, or GOT2 genes have been reported in patients exhibiting neurological symptoms such as global developmental delay, epilepsy, and progressive microcephaly.

METHOD

In this study, we employed exome data analysis of a patient diagnosed with DEE, focusing on the screening of 1896 epilepsy-related genes listed in the HPO and ClinVar databases. Sanger sequencing was subsequently conducted to validate and assess the inheritance pattern of the identified variants within the family. The evolutionary conservation scores of the mutated residues were evaluated using the ConSurf Database. Furthermore, the impacts of the causative variations on protein stability were analyzed through I-Mutant and MuPro bioinformatic tools. Structural comparisons between wild-type and mutant proteins were performed using PyMOL, and the physicochemical effects of the mutations were assessed using Project Hope.

RESULTS

Exome data analysis unveiled the presence of novel compound heterozygous mutations in the GOT2 gene coding for mitochondrial glutamate aspartate transaminase. Sanger sequencing confirmed the paternal inheritance of the p.Asp257Asn mutation and the maternal inheritance of the p.Arg262Cys mutation. The affected individual exhibited plasma metabolic disturbances, including hyperhomocysteinemia, hyperlactatemia, and reduced levels of methionine and arginine. Detailed bioinformatic analysis indicated that the mutations were located within evolutionarily conserved domains of the enzyme, resulting in disruptions to protein stability and structure.

CONCLUSION

Herein, we describe a case with DEE82 (MIM: # 618721) with pathologic novel biallelic mutations in the GOT2 gene. Early genetic diagnosis of metabolic epilepsies is crucial for long-term neurodevelopmental improvements and seizure control as targeted treatments can be administered based on the affected metabolic pathways.

Metabolic Epilepsy

Inborn errors of metabolism have been considered as an infrequent cause of epilepsy. Improvement in diagnostics has improved the detection of a metabolic basis of recurrent seizures in neonates and children. The term 'metabolic epilepsy' is used to suggest inherited metabolic disorders with predominant epileptic manifestations as well as those where epilepsy is part of the overall neurological phenotype. Several of these disorders are treatable, and the physician should bear in mind the classical ages of presentation. As there are no specific clinical or electrographic features suggestive of metabolic epilepsies, an early suspicion is based on clinical and laboratory clues. Fortunately, with the advancement of gene sequencing technology, a diagnosis of these rare conditions is more straightforward and may not require invasive procedures such as biopsies, multiple metabolic stress-induced testing for abnormalities, and cerebrospinal fluid analysis. A gene panel may suffice in most cases and can be done from a blood sample. In many countries, many treatable metabolic disorders are now part of the neonatal screen. Early diagnosis and treatment of these disorders can result in the prevention of a full-scale metabolic crisis and improvement of neurological outcomes. Long-term neurological outcomes are variable and additional therapies may be required.

Metabolic epilepsy in hyperprolinemia type II due to a novel nonsense ALDH4A1 gene variant

Hyperprolinemia type II (HPII) is a rare autosomal recessive disorder of proline degradation pathway due to deficiency of delta-1-pyrroline-5-carboxylate dehydrogenase. Pathogenic variants in the ALDH4A1 gene are responsible for this disorder. We here describe an 11-month-old infant with recurrent seizures refractory to multiple antiepileptic drugs. She was hospitalized in view of acute-onset encephalopathy, exacerbation of generalized seizures following an upper respiratory infection. Laboratory investigation revealed significantly elevated proline levels in dried blood spots. DNA sample of the child was subjected to a targeted next-generation sequencing gene panel for hyperprolinemias. We detected a novel nonsense homozygous variant in the ALDH4A1 gene in the child and the heterozygous variant of the same in both the parents. Based on the location of the variant i.e. in the last exon, truncated protein is expected to be expressed by skipping nonsense-mediated decay and such point-nonsense variants could be an ideal target for readthrough drugs to correct genetic defects.

ADSL Deficiency - The Lesser-Known Metabolic Epilepsy in Infancy

Adenylosuccinate lyase deficiency is a rare inherited disorder of purine metabolism causing severe neurological impairment ranging from early-onset neonatal epileptic encephalopathy to progressive psychomotor retardation and autism in later life. Diagnostic workup involves the measurement of toxic succinyl purines in body fluids and gene sequencing. The authors describe a 13-mo-old girl with compound heterozygous variants in the ADSL gene, presenting as early-onset seizures, severe neurological impairment, development delay, and hypotonia. Neuroimaging revealed cerebral atrophy, delayed myelination and diffusion restriction in bilateral basal ganglia, thalamus and periventricular white matter. The present case highlights ADSL deficiency as a rare cause of metabolic epilepsy that needs timely recognition and prevention of unnecessary investigations.

Contemporary scope of inborn errors of metabolism involving epilepsy or seizures

Many inborn errors of metabolism may present with epilepsy or seizures, however, current scope of these diseases is unknown. Due to available precision medicine approaches in many inborn errors of metabolism and sophisticated traditional diagnostics, this group of disorders is of special relevance to clinicians. Besides, as current treatment is challenging and unsuccessful in more than 30% of all epilepsy patients, these diseases may provide valuable models for ictogenesis and epileptogenesis studies and potentially pave the ways to identification of novel treatments. The aim of this study was to elucidate genetic architecture of inborn errors of metabolism involving epilepsy or seizures and to evaluate their diagnostic approaches. After extensive search, 880 human genes were identified with a considerable part, 373 genes (42%), associated with inborn errors of metabolism. The most numerous group comprised disorders of energy metabolism (115, 31% of all inborn errors of metabolism). A substantial number of these diseases (26%, 97/373) have established specific treatments, therefore timely diagnosis comes as an obligation. Highly heterogenous, overlapping and non-specific phenotypes in most of inborn errors of metabolism presenting with epilepsy or seizures usually preclude phenotype-driven diagnostics. Besides, as traditional diagnostics involves a range of specialized metabolic tests with low diagnostic yields and is generally inefficient and lengthy, next-generation sequencing-based methods were proposed as a cost-efficient one-step way to shorten "diagnostic odyssey". Extensive list of 373 epilepsy- or seizures-associated inborn errors of metabolism genes may be of value in development of gene panels and as a tool for variants' filtration.

Overexpression of recombinant human antiquitin in E. coli: partial enzyme activity in selected ALDH7A1 missense mutations associated with pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy (PDE) is an autosomal recessive disorder characterized by early onset seizures responsive to pyridoxine and caused by a defect in the α-aminoadipic semialdehyde dehydrogenase (antiquitin) gene (ALDH7A1). We selected four PDE-associated missense ALDH7A1 mutations, p.V367F, p.F410L, p.Q425R, and p.C450S, generated them in a recombinant human antiquitin cDNA with expression in E. coli at either 30°C or 37°C. One mutation, p.C450S, demonstrated substantial activity after expression at both temperatures, potentially contributing to milder biochemical and clinical phenotypes. The p.Q425R mutation yielded no activity at either temperature. The other two mutations yielded significant enzymatic activity at 30°C and markedly reduced activity at 37°C. For these latter three mutations, the markedly reduced or absent enzymatic activity resulting from expression at 37°C may be consistent with pathogenicity.

Metabolic epilepsy: an update

Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. Presentation is usually in the neonatal period or infancy but can occur at any time, even in adulthood. Seizures are frequent symptom in inborn errors of metabolism, with no specific seizure types or EEG signatures. The diagnosis of a genetic defect or an inborn error of metabolism often results in requests for a vast array of biochemical and molecular tests leading to an expensive workup. However a specific diagnosis of metabolic disorders in epileptic patients may provide the possibility of specific treatments that can improve seizures. In a few metabolic diseases, epilepsy responds to specific treatments based on diet or supplementation of cofactors (vitamin-responsive epilepsies), but for most of them specific treatment is unfortunately not available, and conventional antiepileptic drugs must be used, often with no satisfactory success. In this review we present an overview of metabolic epilepsies based on various criteria such as treatability, age of onset, seizure type, and pathogenetic background.