Clinicopathologic Findings of CARS2 Mutation

Role of Mutations of Mitochondrial Aminoacyl-tRNA Synthetases Genes on Epileptogenesis

Mitochondria are the structures in cells that are responsible for producing energy. They contain a specific translation unit for synthesizing mitochondria-encoded respiratory chain components: the mitochondrial DNA (mt DNA). Recently, a growing number of syndromes associated with the dysfunction of mt DNA translation have been reported. However, the functions of these diseases still need to be precise and thus attract much attention. Mitochondrial tRNAs (mt tRNAs) are encoded by mt DNA; they are the primary cause of mitochondrial dysfunction and are associated with a wide range of pathologies. Previous research has shown the role of mt tRNAs in the epileptic mechanism. This review will focus on the function of mt tRNA and the role of mitochondrial aminoacyl-tRNA synthetase (mt aaRS) in order to summarize some common relevant mutant genes of mt aaRS that cause epilepsy and the specific symptoms of the disease they cause.

Severe neonatal onset neuroregression with paroxysmal dystonia and apnoea: Expanding the phenotypic and genotypic spectrum of CARS2-related mitochondrial disease

Disorders of mitochondrial function are a collectively common group of genetic diseases in which deficits in core mitochondrial translation machinery, including aminoacyl tRNA synthetases, are key players. Biallelic variants in the CARS2 gene (NM_024537.4), which encodes the mitochondrial aminoacyl-tRNA synthetase for cysteine (CARS2, mt-aaRScys; MIM*612800), result in childhood onset epileptic encephalopathy and complex movement disorder with combined oxidative phosphorylation deficiency (MIM#616672). Prior to this report, eight unique pathogenic variants in the CARS2 gene had been reported in seven individuals. Here, we describe a male who presented in the third week of life with apnoea. He rapidly deteriorated with paroxysmal dystonic crises and apnoea resulting in death at 16 weeks. He had no evidence of seizure activity or multisystem disease and had normal brain imaging. Skeletal muscle biopsy revealed a combined disorder of oxidative phosphorylation. Whole-exome sequencing identified biallelic variants in the CARS2 gene: one novel (c.1478T>C, p.Phe493Ser), and one previously reported (c.655G>A, p.Ala219Thr; rs727505361). Northern blot analysis of RNA isolated from the patient's fibroblasts confirmed a clear defect in aminoacylation of the mitochondrial tRNA for cysteine (mt-tRNACys). To our knowledge, this is the earliest reported case of CARS2 deficiency with severe, early onset dystonia and apnoea, without epilepsy.

Shared and distinct ultra-rare genetic risk for diverse epilepsies: A whole-exome sequencing study of 54,423 individuals across multiple genetic ancestries

Identifying genetic risk factors for highly heterogeneous disorders like epilepsy remains challenging. Here, we present the largest whole-exome sequencing study of epilepsy to date to investigate rare variants that confer risk for a spectrum of epilepsy syndromes. With an unprecedented sample size of >54,000 human exomes, composed of 20,979 deep-phenotyped patients with epilepsy and 33,444 controls, we replicate previous gene findings at exome-wide significance; using a hypothesis-free approach, we identify potential novel associations. Most discoveries are specific to a particular subtype of epilepsy, highlighting distinct genetic contributions to different epilepsies. Combining evidence from rare single nucleotide/short indel-, copy number-, and common variants, we find convergence of different genetic risk factors at the level of individual genes. Further comparing to other exome-sequencing studies, we implicate shared rare variant risk between epilepsy and other neurodevelopmental disorders. Our study also demonstrates the value of collaborative sequencing and deep-phenotyping efforts, which will continue to unravel the complex genetic architecture underlying the heterogeneity of epilepsy.

Generation of an iPSC line from a patient with early-onset epileptic encephalopathy carrying CARS2 (p.G476R) mutation

Mutations in CARS2 gene, encoding for the mitochondrial cysteinyl-tRNA synthetase, has been reported to be associated with early-onset epileptic encephalopathy (EOEE). Here, we generated an induced pluripotent stem cell (iPSC) line from the human dermal fibroblasts (HDFs) of an one-year-old boy with EOEE carrying homozygous c.1426G > A mutation in CARS2 gene. These iPSCs exhibited stable amplification, expressed pluripotent markers, and differentiated spontaneously into three germ layers in vitro.

Expanding the electro-clinical phenotype of CARS2associated neuroregression

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Pathogenic variants in cysteinyl-tRNA synthetase-2 (CARS2) gene have recently been described to cause severe myoclonic epilepsy, neuroregression, progressive audio-visual impairment and movement disorder.

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We present an 11-year-old boy with neuroregression, dysfluent speech, aggressive behavior, tremors and ESES pattern on EEG

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Our case expands the existing electro-clinical phenotype of CARS2 associated neuroregression.

Biallelic variants in CARS2 (Cysteinyl-tRNA synthetase 2; MIM*612800), are known to cause combined oxidative phosphorylation deficiency 27 (MIM#616672), characterized by severe myoclonic epilepsy, neuroregression and complex movement disorders. To date, six individuals from five families have been reported with variants in CARS2. Herein, we present an 11-year-old boy who presented with neuroregression, dysfluent speech, aggressive behavior and tremors for 2 years. An electroencephalogram (EEG) revealed a highly abnormal background with generalized spike-and-wave discharges suggestive of Electrical Status Epilepticus during Sleep (ESES). A known homozygous c.655G > A(p.Ala219Thr) pathogenic variant in exon 6 of the CARS2(NM_024537.4) was identified on exome sequencing. Our report expands the electro-clinical spectrum of the phenotype with presence of severe behavioral abnormalities, continuous tremors and ESES pattern on EEG, not previously reported.

Clinical Attributes and Electroencephalogram Analysis of Patients With Varying Alpers' Syndrome Genotypes

Alpers' syndrome is an early inceptive neurodegenerative disorder with a poor prognosis, characterized by developmental regression, intractable epilepsy, and hepatic dysfunction. Candidate genes, such as POLG, PARS2, CARS2, FARS2, NARS2, and GABRB2 are distinguished and registered following research on large cohorts that portray the clinical phenotype in such patients using expanded access to whole-exome sequencing (WES). In this study, we aimed to better understand the electroencephalogram (EEG) characteristics and clinical phenotype of different genotypes of the Alpers' syndrome, which are currently insufficiently studied. We conducted a study on seven patients with Alpers' syndrome who received treatment in Beijing Children's Hospital and had a detailed clinical EEG. Furthermore, a substantial literature search of the Chinese Biomedical Literature Database, PubMed, and Cochrane Central Register of Controlled Trials EMBASE was also conducted, which revealed a total of 22 reported cases between January 2008 to January 2021. We analyzed 29 cases of Alpers' syndrome caused by different gene variants, of which 22 cases were related to POLG gene mutation and 7 cases were related to PARS2, CARS2, FARS2, NARS2, and GABRB2 gene mutation, and found that patients with distinctive pathogenic variants exhibited comparable phenotypes and similar EEG patterns. And we defined EEG characteristics found specifically in Alpers' syndrome. Rhythmic high-amplitude delta with superimposed (poly) spikes (RHADS) is a characteristic EEG finding in the early stages of Alpers' syndrome and is a kind of epileptic phenomenon, which can provide clues for the early diagnosis of the disease.

[Mutations in aminoacyl-tRNA synthetase genes: an analysis of 10 cases]

OBJECTIVE

To study the clinical features of the diseases associated with aminoacyl-tRNA synthetases (ARS) deficiency.

METHODS

A retrospective analysis was performed of the clinical and gene mutation data of 10 children who were diagnosed with ARS gene mutations, based on next-generation sequencing from January 2016 to October 2019.

RESULTS

The age of onset ranged from 0 to 9 years among the 10 children. Convulsion was the most common initial symptom (7 children). Clinical manifestations included ataxia and normal or mildly retarded intellectual development (with or without epilepsy; n=4) and onset of epilepsy in childhood with developmental regression later (n=2). Some children experienced disease onset in the neonatal period and had severe epileptic encephalopathy, with myoclonus, generalized tonic-clonic seizure, and convulsive seizure (n=4); 3 had severe delayed development, 2 had feeding difficulty, and 1 had hearing impairment. Mutations were found in five genes: 3 had novel mutations in the AARS2 gene (c.331G>C, c.2682+5G>A, c.2164C>T, and c.761G>A), 2 had known mutations in the DARS2 gene (c.228-16C>A and c.536G>A), 1 had novel mutations in the CARS2 gene (c.1036C>T and c.323T>G), 1 had novel mutations in the RARS2 gene (c.1210A>G and c.622C>T), and 3 had novel mutations in the AARS gene (c.1901T>A, c.229C>T, c.244C>T, c.961G>C, c.2248C>T, and Chr16:70298860-70316687del).

CONCLUSIONS

A high heterogeneity is observed in the clinical phenotypes of the diseases associated with the ARS deficiency. A total of 14 novel mutations in 5 genes are reported in this study, which enriches the clinical phenotypes and genotypes of the diseases associated with ARS deficiency.

Genetic basis of neurodevelopmental disorders in 103 Jordanian families

We recruited 103 families from Jordan with neurodevelopmental disorders (NDD) and patterns of inheritance mostly suggestive of autosomal recessive inheritance. In each family, we investigated at least one affected individual using exome sequencing and an in-house diagnostic variant interpretation pipeline including a search for copy number variation. This approach led us to identify the likely molecular defect in established disease genes in 37 families. We could identify 25 pathogenic nonsense and 11 missense variants as well as 3 pathogenic copy number variants and 1 repeat expansion. Notably, 11 of the disease-causal variants occurred de novo. In addition, we prioritized a homozygous frameshift variant in PUS3 in two sisters with intellectual disability. To our knowledge, PUS3 has been postulated only recently as a candidate disease gene for intellectual disability in a single family with three affected siblings. Our findings provide additional evidence to establish loss of PUS3 function as a cause of intellectual disability.