The NM_000138 c.3058A>G, is a missense variant in FBN1 predicted to cause a substitution of a Threonine by Alanine at amino acid 1020 (p.Thr1020Ala). This variant was found in 12 probands with variable phenotypes, mostly thoracic aortic aneurysm or a marfanoid habitus. One proband additionally presented ectopia lentis. Two of these probands carried two other pathogenic variants: a variant in FBN1 (BP2) and a variant in TGFBR1 (BP5). The variant in FBN1 has been reported ten times in ClinVar: 8 times as likely benign and two times as a variant of uncertain significance (Variation ID: 42325). The variant has been reported in the literature in multiple affected individuals including one individual with classical Marfan syndrome (PMID: 11175294), one individual with incomplete Marfan syndrome (PMID: 18435798), one patient with MASS syndrome (PMID: 25944730), and an individual with bicuspid aortic valve and aortic root aneurysm (PMID: 28387797). This variant has also been reported in 3 patients with Lujan-Fryns syndrome (PMID: 19293843, PMID: 28027854), including two brothers with marfanoid habitus, learning disabilities without cardiac defects (PMID: 28027854). These brothers also share a variant in MECP2. Segregation analysis in one family showed that the variant was also present in four additional family members, none of which had aortic aneurysm, two had a marfanoid habitus This variant has been identified in 80 individuals of European-non-Finnish origin (MAF: 0.062%) in gnomad v2.1.1 (https://gnomad.broadinstitute.org/) (BS1). 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 likely benign for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: BS1, BP2, BP5.