The c.68G>T (p.Gly23Val) variant in MRAS is a missense variant predicted to cause substitution of glycine by valine at amino acid 23. This variant has a minor allele frequency of 0.00008624% (1/1159522) in the European (non-Finnish) population in gnomAD v4 (PM2_Supporting). The computational predictor REVEL gives a score of 0.923, which is above the threshold of 0.7, evidence that correlates with impact to MRAS function (PP3). This variant resides within the P-loop (amino acids 20 – 27) of MRAS that is defined as a critical functional domain by the ClinGen RASopathy VCEP (PM1). This variant has been identified in 1 individual with features of RASopathy (PS4_Supporting; PMID:28289718). This variant has been identified as a de novo occurrence with confirmed parental relationships in 1 individual with features of RASopathy (PS2; PMID:28289718). RAS and ERK activation assays in HEK293T/17 showed constitutively active forms of MRAS indicating that this variant impacts protein function (PMID:28289718) (PS3_Moderate). Given the Moderate strength of gene-disease relationship between MRAS and autosomal dominant RASopathy, ClinGen’s sequence variant interpretation working group does not recommend the classification of variants in this gene beyond likely pathogenic. Based on ACMG/AMP criteria alone, this variant has enough supporting evidence to be classified as pathogenic; however, the RASopathy VCEP has downgraded this classification to likely pathogenic based on ClinGen policy. In summary, this variant currently meets the criteria to be classified as likely pathogenic for autosomal dominant RASopathy based on the ACMG/AMP criteria applied, as specified by the ClinGen RASopathy VCEP: PS2, PS3_M, PM1, PS4_P, PM2_P, PP3. (RASopathy VCEP specifications version 1.1; 9/17/2024)