The NM_002524.5:c.173C>T variant in NRAS 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_P). The computational predictor REVEL gives a score of 0.959, which is above the threshold of 0.7, evidence that correlates with impact to NRAS function (PP3). This variant resides within the Switch 2 region (amino acids 57 – 64), of NRAS that is defined as a critical functional domain (PM1). 2 different missense variants, (KRAS):c.173C>T (p.Thr58Ile) (PMID: 16474405; ClinVar ID: 12588) and (HRAS):c.173C>T (p.Thr58Ile) (PMID: 18247425; ClinVar ID: 12610), in the same codon have been classified as pathogenic for RASopathy by the ClinGen RASopathy VCEP (PS1). This variant has been reported in 1 proband with RASopathy (PS4_Supporting; PMID:28594414). ERK (and AKT) activation assays in HEK293T cells promoted enhanced activation of ERK and AKT, even in the absence of stimulation. Additionally, a higher level of NRASThr58Ile in its GTP-bound, active form was observed, indicating that this variant causes gain of function (PMID: 28594414) (PS3_Moderate). In summary, this variant meets the criteria to be classified as pathogenic for autosomal dominant RASopathy based on the ACMG/AMP criteria applied, as specified by the ClinGen RASopathy VCEP: PS1, PS3_Moderate, PM1, PS4_Supporting, PM2_Supporting, PP3. (ClinGen RASopathy VCEP specifications version 2.3; 12/3/2024)