Activity

Filter

Cancel
Date Panel Item Activity
14 actions
Early onset or syndromic epilepsy v2.0 RARS Konstantinos Varvagiannis gene: RARS was added
gene: RARS was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: RARS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: RARS were set to 31814314; 28905880; 24777941
Phenotypes for gene: RARS were set to Leukodystrophy, hypomyelinating, 9 616140
Penetrance for gene: RARS were set to Complete
Review for gene: RARS was set to GREEN
Added comment: Biallelic pathogenic RARS1 variants cause Leukodystrophy, hypomyelinating, 9 (# 616140).

The current review was based primarily on PMID: 31814314 (Mendes et al, 2019) providing details on 20 affected individuals from 15 families. 5 of these patients were included in a previous publication (Wolf et al, 2014 - PMID: 24777941) sharing authors with this study.

Clinical presentation and severity can be highly variable. However, among the 15 patients of relevant age (5/20 deceased at an early age), ID was observed in 13 (in 6/13 mild-moderate, in 7/13 severe/profound). Epilepsy was reported in half (10/20) with seizures being refractory to treatment in most and the phenotype corresponding to an infantile epileptic encephalopathy. DD and seizures were the presenting feature in 7 and 5 patients respectively, while in other cases presenting features were less specific (eg. failure to thrive in 1/20, irritabilty in 2/20). As a result the gene appears to be relevant to both DD/ID and epilepsy panels.

RARS1 encodes the cytoplasmic arginyl-tRNA synthetase 1, which is a component of the aminoacyl-tRNA synthetase complex (OMIM and Wolf et al, 2014 - PMID: 24777941). Aminoacyl-tRNA synthetases catalyze the aminoacylation ('charging') of tRNA by (with) their cognate amino acid.

Utilisation of alternative initiation codons, from a single mRNA transcript, results in translation of a long and a short protein isoform (Zheng et al 2006 - PMID: 16430231). The long isoform is needed for the formation of the multi-synthetase complex (MSC), while the short is free in the cytoplasm and does not have any interaction with the MSC. The long isoform appears to be essential for protein synthesis (discussed with several refs provided in PMID: 28905880 - Nafisinia et al, 2017).

The role of variants has been supported in several patients by additional studies - among others :
[PMID 31814314] Impaired Arginyl-tRNA synthetase activity was demonstrated in fibroblasts from 3 patients. Activity was normal in one additional individual compound heterozygous for a variant affecting initiation codon and a missense one. Western blot however demonstrated presence mainly of the short protein isoform. The authors suggest that this isoform possibly contributed to enzymatic activity. The long isoform which is needed for the MSC complex was only represented by a faint band in the Western Blot of the same individual.
[PMID: 28905880] Using fibroblasts from an affected subject homozygous for a missense variant (NM_002887.3:c.5A>G / p.Asp2Gly) and controls, a 75% reduction of the long isoform was shown upon WB. The short isoform was present at similar levels. As the N-terminus (of the long isoform) mediates interaction with the MSC (and AIMP1), assembly of the latter was 99% reduced in patient fibroblasts. Proliferation of patient fibroblasts was significantly reduced when cultured in a medium with limited arginine, a finding which was thought to reflect inefficient protein synthesis.

Mutations in other genes encoding for aminoacyl-tRNA synthetases (eg. AARS1, VARS1) or scaffolding proteins of the multisynthetase complex (eg. AIMP1 and AIMP2) lead to neurodevelopmental disorders with overlapping phenotype [most genes rated green in both the ID and epilepsy panel].
Sources: Literature
Early onset or syndromic epilepsy v1.263 VARS Louise Daugherty Tag new-gene-name tag was added to gene: VARS.
Early onset or syndromic epilepsy v1.263 VARS Louise Daugherty commented on gene: VARS
Early onset or syndromic epilepsy v1.191 VARS Rebecca Foulger Source Wessex and West Midlands GLH was added to VARS.
Early onset or syndromic epilepsy v1.190 VARS Rebecca Foulger Source NHS GMS was added to VARS.
Early onset or syndromic epilepsy v1.189 VARS Rebecca Foulger reviewed gene: VARS: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.188 VARS Tracy Lester reviewed gene: VARS: Rating: GREEN; Mode of pathogenicity: ; Publications: 26539891, 29691655 ; Phenotypes: Neurodevelopmental disorder with microcephaly seizures and cortical atrophy, 617802; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v0.553 VARS Sarah Leigh Marked gene: VARS as ready
Early onset or syndromic epilepsy v0.553 VARS Sarah Leigh Added comment: Comment when marking as ready: Associated with phenotype in OMIM and not in Gen2Phen. Seizures identified in sufficient unrelated cases for VARS to be rated green on the Genetic Epilepsy syndromes panel.
Early onset or syndromic epilepsy v0.553 VARS Sarah Leigh Gene: vars has been classified as Green List (High Evidence).
Early onset or syndromic epilepsy v0.553 VARS Sarah Leigh Phenotypes for gene: VARS were changed from # 617802. NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, SEIZURES, AND CORTICAL ATROPHY; NDMSCA to Neurodevelopmental disorder with microcephaly, seizures, and cortical atrophy 617802
Early onset or syndromic epilepsy v0.552 VARS Sarah Leigh Classified gene: VARS as Green List (high evidence)
Early onset or syndromic epilepsy v0.552 VARS Sarah Leigh Gene: vars has been classified as Green List (High Evidence).
Early onset or syndromic epilepsy v0.505 VARS Konstantinos Varvagiannis gene: VARS was added
gene: VARS was added to Genetic Epilepsy Syndromes. Sources: Expert Review,Literature
Mode of inheritance for gene: VARS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: VARS were set to 26539891; 29691655; 30275004
Phenotypes for gene: VARS were set to # 617802. NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, SEIZURES, AND CORTICAL ATROPHY; NDMSCA
Penetrance for gene: VARS were set to Complete
Review for gene: VARS was set to GREEN
Added comment: PMID: 26539891 is the first report on individuals with biallelic pathogenic variants in VARS. 3 individuals from 2 consanguineous families are briefly reported. The phenotype was similar in all 3, consisting of severe developmental delay, microcephaly, seizures and cortical atrophy. Subjects from the first family were homozygous for a missense variant in the tRNA synthetase catalytic domain [p.(L885F)]. The patient from the second family was homozygous for a missense SNV affecting the anticodon-binding domain [p.(R1058Q)].

PMID: 29691655 reports on a further patient born to non-consanguineous parents, with 2 in-trans pathogenic variants in VARS. The phenotype consisted of progressive microcephaly (OFC at birth -2SD, at the age of 2 months -4SD), global developmental delay, seizures and progressive cerebral and cerebellar atrophy. An affected brother presented with more severe phenotype (OFC -6SD at birth and -8SD at 2 months of age), seizures, hearing loss but was deceased and unavailable for genetic testing. cDNA studies demonstrated absence of the reference allele for the missense mutation downstream the splice variant (in line with a reduced or absent mRNA allele harboring the splice variant). Similarly, mRNA expression studies demonstrated 50-60% reduction in the transcripts (due to NMD of the allele with the splice SNV). Western blot showed severe reduction in protein levels (more pronounced compared to what would be expected by mRNA expression) presumably secondary to decreased protein stability due to the missense variant. Severe defects in aminoacylation were further confirmatory of a pathogenic role of these variants. The missense variant was affecting the anticodon-binding domain, important for aminoacylation.

PMID: 30275004 reports on 2 siblings with developmental delay, intellectual disability, severe speech impairment and microcephaly, similar to what has been described for the disorder. Clinical findings were somewhat different from previous studies in that microcephaly was acquired, while seizures and cortical atrophy were not part of the phenotype. Both sibs were compound heterozygous for 2 missense variants, though only one of these mutations affected the anticodon binding domain and the other was in the N-terminal region of the protein. Previous metabolic studies and extensive genetic testing (karyotype, CMA, MECP2, FMR1) was normal.

Epilepsy was a feature in 4 of the 6 individuals for whom genetic testing was possible (or 5/7 in total).

VARS belongs to the family of amino acyl-tRNA synthetases (ARSs). Mutations in several cytoplasmic ARSs are associated with severe neurological manifestations including seizures, intellectual disability associated with microcephaly.

VARS is included in gene panels for intellectual disability (but not for epilepsy) offered by different diagnostic labs.

As a result this gene can be considered for inclusion in the ID and epilepsy panel as green (or amber).
Sources: Expert Review, Literature