The c.779C>T (p.Thr260Ile) variant in RAF1 was absent from large population databases (PM2; gnomad.broadinstitute.org). It occurs in the CR2 domain of the protein, which has been identified as a region important for protein function (PM1, 29493581). In vitro functional assays indicate that this variant may impact protein function (PS3; PMID: 20679480). The variant is located in the RAF1 gene, which has been defined by the ClinGen RASopathy Expert Panel as a gene with a low rate of benign missense variants and pathogenic variants are common (PP2; PMID: 29493581). Computational prediction tools and conservation analyses do not provide strong support for or against an impact to the protein. This variant has been observed in multiple probands who lacked consistent RASopathy phenotypes; however, many probands presented with cardiomyopathy (PMID: 17603483; Blueprint Genetics internal data, SCV000264163.2; Invitae internal data, SCV000824563.1; Ambry internal data, SCV000740058.2; GeneDx internal data, SCV000582743.4). Although criteria suggest that this variant is likely pathogenic given its location and in vitro functional studies, the lack of clear clinical presentations of a RASopathy phenotype supports that this variant is of uncertain significance at this time. RASopathy-specific ACMG/AMP criteria applied: PS3, PM1, PM2, PP2.