ClinVar

Description

Variant summary: The HRAS c.183G>T (p.Gln61His) variant causes a missense change involving the alteration of a non-conserved nucleotide. 2/4 in silico tools predict a benign outcome for this variant (SNPsandGO not captured due to low reliability index). The variant alters a GEF interaction site of conserved H_Ras_like domain and was shown to have a reduced hydrolyzed GTPase activity resulting in a constitutively active protein (Bollag, 1991; Der 1986). The variant of interest is absent from broad control datasets of ExAC or gnomAD (~100996 and 276982 chrs tested, respectively). The variant has not, to our knowledge, been reported as germline mutation in individuals diagnosed with Costello (CS) or Noonan Spectrum Related Disorders (NSRD) via publications and/or reputable databases/clinical diagnostic laboratories. Oncogenic Ras codons 12, 13 and 61 are well known as the primary sites where activating somatic mutations result in a constitutively active protein characterized by a reduced GAP action and/or intrinsic GTPase activity. The p.Gln61His is vastly reported in the literature as a somatic variant, identified in melanoma, metaplastic breast carcinoma, lung cancer, head and neck cancer, and other types of tumors. The c.183G>T was identified in a prenatal sample with negative MCC referred for genetic testing due to abnormal ultrasound finding (cystic hygroma, fetal edema and cardiac defect). Considering all evidence and ACMG guidelines, the variant of interest is classified as Likely Pathogenic.