ClinVar Genomic variation as it relates to human health

The c.173C>T variant in the HRAS gene is a missense variant predicted to cause substitution of threonine by isoleucine at amino acid 58 (p.Thr58Ile). This variant is absent from gnomAD v2.1.1 (PM2_Supporting). The computational predictor REVEL gives a score of 0.777, which is above the threshold of 0.7, evidence that correlates with impact to HRAS function (PP3). This variant resides within a region (amino acids 57 – 64), of HRAS that is defined as a critical functional domain by the ClinGen RASopathy VCEP (PM1). The p.Thr58Ile variant in HRAS is analogous to the same previously established amino acid change in the KRAS gene and the ClinGen RASopathy Expert Panel has defined that the pathogenicity of analogous variants in the HRAS and KRAS genes are correlated based on the assumption that a known functional residue in one gene is equivalent to other functions within that subgroup (PS1). At least 4 independent occurrences of this variant have been detected in patients with a RASopathy, of which 1 was reported as a de novo occurrence (PS2, PS4_Moderate; CeGaT Center for Human Genetics, ClinVar SCV003916655.13; PMIDs: 22488832, 18247425, 23321623, 26888048). In summary, this variant meets criteria to be classified as pathogenic for autosomal dominant RASopathies based on the ACMG/AMP criteria applied, as specified by the ClinGen RASopathy Variant Curation Expert Panel: PS1, PS2, PS4_Moderate, PM1, PM2_Supporting, PP3 (Specification Version 2.3, 12/3/2024)

The Thr58Ile variant in HRAS has been reported in three individuals with clinica l features of Costello syndrome (Gripp 2008, Gripp 2012, LMM unpublished data). It was identified to occur de novo in two of these individuals and segregated w ith disease in one affected relative from one of these families. This variant wa s absent from large population studies. Computational prediction tools and conse rvation analysis suggest that this variant may impact the protein, though this i nformation is not predictive enough to determine pathogenicity. In summary, this variant meets our criteria to be classified as pathogenic (http://pcpgm.partner s.org/LMM).

Based on the classification scheme VCGS_Germline_v1.3.4, this variant is classified as Pathogenic. Following criteria are met: 0101 - Gain of function is a known mechanism of disease in this gene and is associated with Costello syndrome (MIM#218040) [PMID: 31222966]. (I) 0107 - This gene is associated with autosomal dominant disease. (I) 0115 - Variants in this gene are known to have variable expressivity (GeneReviews).(I) 0200 - Variant is predicted to result in a missense amino acid change from threonine to isoleucine. (I) 0251 - This variant is heterozygous. (I) 0301 - Variant is absent from gnomAD (both v2 and v3). (SP) 0309 - An alternative amino acid change at the same position has been observed in gnomAD (v2) (1 heterozygote, 0 homozygotes). (I) 0501 - Missense variant consistently predicted to be damaging by multiple in silico tools or highly conserved with a major amino acid change. (SP) 0602 - Variant is located in a hotspot region or cluster of pathogenic variants in the Ras domain (Decipher; PMID 29493581). (SP) 0801 - This variant has strong previous evidence of pathogenicity in unrelated individuals. This variant has been reported as de novo in at least two individuals with Costello syndrome (PMID 18247425; PMID 26888048). It has also been reported in a father and child with an attenuated Costello syndrome phenotype (PMID 22488832). This variant has been classified as pathogenic by the ClinGen RASopathy Variant Curation Expert Panel (ClinVar). (SP) 1102 - Strong phenotype match for this individual. (SP) 1208 - Inheritance information for this variant is not currently available in this individual. (I) Legend: (SP) - Supporting pathogenic, (I) - Information, (SB) - Supporting benign

This sequence change replaces threonine, which is neutral and polar, with isoleucine, which is neutral and non-polar, at codon 58 of the HRAS protein (p.Thr58Ile). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individual(s) with clinical features of Costello syndrome (PMID: 18247425, 22488832, 26888048). In at least one individual the variant was observed to be de novo. ClinVar contains an entry for this variant (Variation ID: 12610). Invitae Evidence Modeling incorporating data from in vitro experimental studies (internal data) indicates that this missense variant is expected to disrupt HRAS function with a positive predictive value of 95%. For these reasons, this variant has been classified as Pathogenic.

PS1, PS4_supporting, PM1, PM2, PP5 The HRAS c.173C>T variant is a single nucleotide change from a cytosine to a thymine at position 173 which is predicted to substitute the amino acid threonine at position 58 in the protein to isoleucine. The variant is located in exon 3. This variant has been reported in the literature in patients with Costello syndrome, and this particular variant appears to be associated with an attenuated phenotype and has been described in a father and son (PMID: 22488832; PMID: 18247425) (PS4_supporting). The variant is in dbSNP (rs121917758) but is absent from population databases (PM2). This variant has been classified by the ClinGen RASopathy Variant Curation Expert Panel as Pathogenic and is reported as Pathogenic in the ClinVar database (Variation ID: 12610) (PP5). This variant was detected in both the affected child and her mother.

HRAS: PS2, PM1, PM2, PS4:Moderate, PP3

The HRAS c.173C>T variant is predicted to result in the amino acid substitution p.Thr58Ile. This variant has been repeatedly confirmed de novo in individuals with clinical features of Costello syndrome (Gripp et al. 2008. PubMed ID: 18247425; Gripp et al. 2012. PubMed ID: 22488832; Hiippala et al. 2016. PubMed ID: 26888048). This variant has not been reported in a large population database, indicating this variant is rare. This variant has been interpreted as pathogenic by the ClinGen RASopathy Variant Curation Expert Panel (https://www.ncbi.nlm.nih.gov/clinvar/variation/12610/). This variant is interpreted as pathogenic.