The NM_00138 c.3509G>A, is a missense variant in FBN1 predicted to cause a substitution of an arginine acid by histidine at amino acid 1170 (p.Arg1170His). This variant has been previously reported in several apparently unrelated individuals with Marfan syndrome (PMID 26787436, internal data), incomplete Marfan syndrome, including with skeletal features and/or mitral valve prolapse (PMID 7870075, 9837823, 17418587, 17627385, 17657824), in individuals with isolated thoracic aortic aneurysm and/or dissection (internal data) and in other phenotypes like arterial dissection and venous bleeding (internal data). This variant was found to segregate with disease in seven affected individuals with incomplete Marfan syndrome from three families (PMID 7870075, 9837823, internal data). This variant has been found to co-occur with different pathogenic variants in FBN1 (BP2), TGFBR1, and TGFRB2 (BP5) (internal data). This variant has been identified in 286 individuals of European non-Finnish origin (MAF: 0.2%) (BA1; https://gnomad.broadinstitute.org/, version 2.1.1). The variant in FBN1 has been reported 21 times in ClinVar: 16 times as likely benign and 5 times as uncertain significance (Variation ID: 16451). Computational prediction tools and conservation analysis are unclear on the predicted impact on the protein (REVEL: 0.502). Functional studies, including in-vitro splicing analysis, found that this variant had no impact on splicing (PMID 21895641, 32123317). The constraint z-score for missense variants affecting FBN1 is 5.06, however due to the presence of benign arguments, PP2 cannot be used. In summary, this variant meets criteria to be classified as benign for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: BA1, BP2, BP5.