NM_00138 c.3422C>T is a missense variant in FBN1 predicted to cause a substitution of a Proline by Leucine at amino acid 1141 (p.Pro1141Leu). This variant has been reported in the literature in at least 3 individuals in association with thoracic aortic aneurysm and dissection (TAAD), MASS syndrome, and features possibly consistent with Marfan syndrome (PMID: 10533071; PMID: 24740214; PMID: 26188975). This variant was also identified in an internal proband with isolated TAAD with a family history highly specific for Marfan syndrome, however it does not segregate with disease in an affected family member (BS4) and therefore PP4 cannot be used. This variant has been previously reported in ClinVar as benign, likely benign, and uncertain significance (Variation ID: 42334). This variant has been identified in 0.026% of individuals of European origin (BS1; https://gnomad.broadinstitute.org/ version 2.1.1). Computational prediction tools and conservation analysis are unclear on the predicted impact on the protein. The constraint z-score for missense variants affecting FBN1 is 5.06, however due to the presence of two 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: BS1, BS4