The NM_00138 c.6163+2dup variant in FBN1 occurs in the intron near the invariant region (+1/2) of the consensus donor splice site; the c.6163+2T nucleotide is moderately conserved. In silico prediction programs (GeneSplicer, MaxEntScan, NNSplice) predict this variant to weaken/ destroy the canonical donor site of this intron, which is expected to disrupt mRNA splicing and result in absent or truncated protein product (PP3). However, this prediction has not been confirmed by RNA functional studies. This variant has been reported five times in ClinVar: once as pathogenic, four times as uncertain significance (Variation ID: 200167). This variant has been reported in individuals with thoracic aortic aneurysm and/or dissection who carried other cardiogenetic variants (GeneDx, Murdoch Childrens Research Institute ClinVar entry). It has also been reported in an individual without structural heart disease (PMID 28659821). This variant is present in 2/113448 (0.0018%) of alleles tested from the European non-Finnish population in gnomAD (https://gnomad.broadinstitute.org/ v2.1.1). 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: PP3.