The NM_00138 c.188A>G is a missense variant in FBN1 predicted to cause a substitution of a tyrosine by cysteine at amino acid 63 (p.Tyr63Cys). This variant was found in a proband with a clinical diagnosis of Marfan syndrome (PMID 17657824) (PP4). This variant in FBN1 has been reported three times in ClinVar: 1 time as uncertain significance, 1 time as likely pathogenic, and 1 time as pathogenic (Variation ID: 547296). This variant has previously been reported in at least two apparently unrelated individuals with ectopia lentis (PMID 25053872, 28941062) and in an individual with a suspected or confimed diagnosis of Marfan syndrome (Centre for Human Genetics, Inc. ClinVar entry) (PS4_mod). This variant has been identified in 1/112420 (0.0004%) individuals of European non-Finnish origin (https://gnomad.broadinstitute.org/version 2.1.1). Computational prediction tools and conservation analysis are inconclusive data with regards to a possible impact on this variant protein function and structure (REVEL: 0.72). The constraint z-score for missense variants affecting FBN1 is 5.06 (PP2). Due to the conflicting evidence, this variant is classified as uncertain significance for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: PS4_Mod, PP2, PP4