ClinVar Genomic variation as it relates to human health

The p.Arg298Cys variant in LMNA has been reported as homozygous in at least 25 N orth African consanguineous families with clinical features of Charcot Marie Too th Disease variant 2B1 (CMT2B1) and has been described as a founder variant in t his population (De Sandre-Giovannoli 2002, Chaouch 2003, Bouhouche 2007, Ben Yao u 2007, Hamadouche 2008). Animal models of this homozygous variant are associate d with some molecular findings but not the phenotypic abnormalities seen in CMT2 B1 patients (Poitelon 2012). This variant has been identified in 6/1111132 of Eu ropean chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.bro adinstitute.org; dbSNP rs59885338) and reported in ClinVar (Variation ID# 14498) ; however its frequency is low enough to be consistent with a recessive carrier frequency. In addition, computational prediction tools and conservation analysis suggest that the p.Arg298Cys variant may impact the protein. In summary, this v ariant meets criteria to be classified as pathogenic for CMT2B1 in an autosomal recessive manner based upon segregation studies, low frequency in controls, and functional evidence. ACMG/AMP Criteria applied: PS4; PP1_Strong; PM2_Supporting; PP3.

This sequence change replaces arginine, which is basic and polar, with cysteine, which is neutral and slightly polar, at codon 298 of the LMNA protein (p.Arg298Cys). This variant is present in population databases (rs59885338, gnomAD 0.005%). This missense change has been observed in individual(s) with autosomal recessive Charcot-Marie-Tooth disease (PMID: 14607793, 17347251, 18549403). It is commonly reported in individuals of North African ancestry (PMID: 11799477, 14607793, 17347251, 18549403). ClinVar contains an entry for this variant (Variation ID: 14498). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt LMNA protein function with a positive predictive value of 95%. For these reasons, this variant has been classified as Pathogenic.

The p.R298C pathogenic mutation (also known as c.892C>T), located in coding exon 5 of the LMNA gene, results from a C to T substitution at nucleotide position 892. The arginine at codon 298 is replaced by cysteine, an amino acid with highly dissimilar properties. This variant has been detected in multiple homozygous individuals with autosomal recessive Charcot-Marie-Tooth disease, has shown segregation with disease in multiple families of Algerian or Moroccan descent, and has been described as a north western African founder mutation (Tazir M et al. Brain, 2004 Jan;127:154-63; Chaouch M et al. Neuromuscul Disord, 2003 Jan;13:60-7; Bouhouche A et al. Brain, 2007 Apr;130:1062-75; Hamadouche T et al. Ann Hum Genet, 2008 Sep;72:590-7). In vitro studies indicate this variant may impact protein function and lead to abnormal nuclear aggregates in some mammalian cell lines (Dreuillet C et al. Biol Cell, 2008 Jan;100:51-61; Anderson CL et al. NPJ Genom Med, 2021 Dec;6:103). In addition, this alteration is predicted to be deleterious by in silico analysis. Based on the supporting evidence, this variant is expected to be causative of autosomal recessive Charcot-Marie-Tooth disease when present along with a second pathogenic variant on the other allele; however, its clinical significance for autosomal dominant cardiomyopathy and other laminopathies is unclear.

The observed missense c.344T>C(p.Leu115Pro) variant in GABRB2 gene has not been reported previously as a pathogenic variant nor a benign variant, to our knowledge. The p.Leu115Pro variant is absent in gnomAD Exomes. This variant has not been submitted to the ClinVar database. Multiple lines of computational evidences (Polyphen - Probably damaging, SIFT - Damaging and MutationTaster - Disease causing) predict a damaging effect on protein structure and function for this variant. The reference amino acid change at this position on GABRB2 gene is predicted as conserved by GERP++ and PhyloP across 100 vertebrates. The amino acid Leu at position 115 is changed to a Pro changing protein sequence and it might alter its composition and physico-chemical properties. For these reasons, this variant has been classified as a Variant of Uncertain Significance (VUS).

Published functional studies demonstrate a damaging effect as cells from R298C homozygous knock in mice showed downregulation of LMNA at both the protein and mRNA level (Poitelon et al., 2012); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; This variant is associated with the following publications: (PMID: 12467734, 14607793, 11799477, 18549403, 17347251, 17536044, 35383421, 16809772, 10939567, 30340945, 34862408, 35449878, 22331516, 31383942)

This missense variant replaces arginine with cysteine at codon 298 of the lamin A/C proteins. Computational prediction suggests that this variant may have a deleterious impact on protein structure and function (internally defined REVEL score threshold >= 0.7, PMID: 27666373). To our knowledge, functional studies have not been reported for this variant. This variant is a well-known founder mutation in North African countries and has been reported to segregate with autosomal recessive Charcot-Marie-Tooth type 2 in affected families (PMID: 11799477, 12467734, 14607793, 17347251; Clinvar variation ID: 14498). Cardiac systems were normal in all of over 20 homozygotes assessed (PMID: 12467734, 14607793). Over 40 heterozygous carriers were reported from these families, who were all asymptomatic except for one individual with nonspecific cardiac abnormalities (PMID: 17536044). This variant has also been reported in another two heterozygous individuals referred for cardiac catheterization (PMID: 32792077). This variant has been identified in 9/250398 chromosomes in the general population by the Genome Aggregation Database (gnomAD). Based on the available evidence, this variant is classified as a Variant of Uncertain Significance for autosomal dominant cardiomyopathy, although it is known to cause autosomal recessive Charcot-Marie-Tooth type 2 (ClinVar variation ID:14498).

The heterozygous c.892C>T (p.Arg298Cys) variant in LMNA is a known pathogenic variant for autosomal recessive Charcot-Marie-Tooth disease, type 2B1(CMT2B1), and has been reported as homozygous in multiple consanguineous families affected with CMT2B1 [PMID: 11799477;PMID: 14607793;PMID: 12467734]. Family-members carrying heterozygous p.Arg298Cys variant were apparently normal [PMID: 11799477;PMID: 14607793;PMID: 12467734]. The variant has been reported in ClinVar database as pathogenic for recessive CMT2B1 disease [Variation ID:14498]. The p.Arg298Cys variant has 0.00002627 allele frequency in the gnomAD(v3) database (4 out of 152,244 heterozygous alleles, no homozygotes) suggesting it is not a common benign variant in the general population. The variant affects an evolutionarily conserved residue and is predicted deleterious by multiple in silico prediction tools. Given that heterozygous carriers of p.Arg298Cys were apparently normal, and due to the absence of evidence supporting its pathogenicity in heterozygous state, the p.Arg298Cys variant in the LMNA gene is reported as a variant of uncertain significance for autosomal dominant familial partial lipodystrophy.

This missense variant replaces arginine with cysteine at codon 298 of the lamin A/C proteins. Computational prediction suggests that this variant may have a deleterious impact on protein structure and function (internally defined REVEL score threshold >= 0.7, PMID: 27666373). To our knowledge, functional studies have not been reported for this variant. This variant is a well-known founder mutation in North African countries and has been reported to segregate with autosomal recessive Charcot-Marie-Tooth type 2 in affected families (PMID: 11799477, 12467734, 14607793, 17347251; Clinvar variation ID: 14498). Cardiac systems were normal in all of over 20 homozygotes assessed (PMID: 12467734, 14607793). Over 40 heterozygous carriers were reported from these families, who were all asymptomatic except for one individual with nonspecific cardiac abnormalities (PMID: 17536044). This variant has also been reported in another two heterozygous individuals referred for cardiac catheterization (PMID: 32792077). This variant has been identified in 9/250398 chromosomes in the general population by the Genome Aggregation Database (gnomAD). Based on the available evidence, this variant is classified as a Variant of Uncertain Significance for autosomal dominant cardiomyopathy, although it is known to cause autosomal recessive Charcot-Marie-Tooth type 2 (ClinVar variation ID:14498).