The NM_00138 c.7892G>A, is a missense variant in FBN1 predicted to cause a substitution of a cysteine by tyrosine at amino acid 2631 (p.Cys2631Tyr). This variant was found in a proband with a clinical diagnosis of Marfan syndrome (MFS) (Internal lab data, PP4). This variant has been reported three times in ClinVar: once as pathogenic, once as likely pathogenic, and once as uncertain significance (Variation ID: 42436). This variant has also been identified in at least 2 individuals with clinical diagnosis of MFS as well as in individuals with clinical features of MFS (PMID 24793577, Invitae ClinVar, internal lab data; PS4_Mod). In one pediatric individual with MFS, this variant found to segregate in an affected sister and was found to be mosaic in the asymptomatic mother (internal lab data). This variant is not present in gnomAD (PM2_sup; https://gnomad.broadinstitute.org/ v2.1.1). This variant affects a cysteine residue in a calcium binding EGF-like domain. Cysteine residues in these domains are believed to be involved in the formation of disulfide bridges which are essential for the protein structure (PM1_strong). Computational prediction tools and conservation analysis suggest that this variant may impact the protein (REVEL: 0.976, PP3). The constraint z-score for missense variants affecting FBN1 is 8.18 (PP2; https://gnomad.broadinstitute.org/ v4.0.0)). In summary, this variant meets criteria to be classified as pathogenic for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: PM1_Strong, PS4_Moderate, PM2_Sup, PP2, PP3, PP4.