BRAF NM_001354609.1:c.1796C>G, Thr599Arg

The c.1796C>G (p.Thr599Arg) variant in BRAF was absent from large population studies (PM2; gnomad.broadinstitute.org). It was observed in 3 probands diagnosed with cardiofaciocutaneous syndrome (PS4_Moderate; PMIDs: 19206169, 28650561; Otto-von-Guericke-Universität Magdeburg internal communication). In two of these patients, as well as one proband with phenotypic features suggestive of a RASopathy but no clinical diagnosis, the variant occurred de novo; parentage was confirmed in 2 of these cases (PS2_VS; PMIDs: 19206169, 28650561; GeneDx internal data, SCV000329761.7). The variant occurs in the CR3 activation domain of BRAF, which has been defined by the ClinGen RASopathy Expert Panel as a region important for protein function (PM1; PMID 29493581). In vitro functional studies provide some evidence that the p.Thr599Arg variant may impact protein function (PS3; PMID: 19206169). Additionally, the variant is located in BRAF, which has been defined by the ClinGen RASopathy Expert Panel as a gene with a low rate of benign missense variants and pathogenic missense variants are common (PP2; PMID: 29493581). In summary, this variant meets criteria to be classified as pathogenic for RASopathies in an autosomal dominant manner. Rasopathy-specific ACMG/AMP criteria applied (PMID:29493581): PS2_VeryStrong, PS3, PS4_Moderate, PM1, PM2, PP2.

Same nucleotide change resulting in same amino acid change has been previously reported as de novoo and observed in at least four similarly affected unrelated individuals (PMID: 19206169, 28650561, PS2, PS4_M). Functional studies provide strong evidence of the variant having a damaging effect on the gene or gene product (PMID: 19206169, PS3). The missense variant is located in a mutational hot spot and/or well-established functional domain in which established pathogenic variants have been reported (PM1). It is not observed in the gnomAD v2.1.1 dataset (PM2). A different missense change at the same codon (p.Thr599Ile) has been reported as pathogenic (VCV000040388.5, PM5). In silico tool predictions suggest damaging effect of the variant on gene or gene product (REVEL: 0.843, 3Cnet: 0.995, PP3). Therefore, this variant is classified as pathogenic according to the recommendation of ACMG/AMP guideline.