NM_00138 c.1073G>A is a missense variant in FBN1 predicted to cause a substitution of a cysteine by tyrosine at amino acid 358(p.Cys358Tyr). This variant has been found in two probands, one with the clinical diagnosis of Marfan syndrome but without a specified phenotype and one with ectopia lentis, thoracic aortic aneurysm and dissection, and a systemic score of 9 (PP4, PS4_supporting; PMID: 35058154; UZG internal data). This variant has been reported two times in ClinVar, once as likely pathogenic and once as of uncertain significance (Variation ID: 549001). This variant is not present in gnomAD (PM2_supporting; https://gnomad.broadinstitute.org/). This variant affects a cysteine residue in a TGFβ binding-protein-like (TB) domain; cysteine residues are believed to be involved in the formation of disulfide bridges which are essential for the protein structure (PM1). Other variants altering this codon are pathogenic or likely pathogenic (p.Cys358Trp, p.Cys358Arg), supporting the functional importance of this amino acid position (PM5). Computational prediction tools and conservation analysis suggest that this variant may impact protein structure or function (PP3). The constraint z-score for missense variants affecting FBN1 is 5.06 (PP2). In summary, this variant meets criteria to be classified as likely pathogenic for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: PM1, PM5, PS4_supporting, PM2_supporting, PP2, PP3, PP4.