NM00138 c.4149_4154del is a deletion predicted to remove the methionine and glycine at amino acid positions 1384 and 1385, respectively, but is not expected to impact the reading frame (PM4). This variant was found to be confirmed as de novo in a young child with a clinical diagnosis of Marfan syndrome (PP4 and PS2; Universitair Ziekenhuis Antwerpen). This variant is not present in gnomAD v2.1.1 (PM2_supporting). p.Gly1385 is known to be involved in interdomain packaging of the protein, and its deletion may disrupt protein structure and/or function (PM1). This variant has not been reported in the published literature or public databases. In summary, this variant meets criteria to be classified as pathogenic for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: PS2, PM1, PM4, PP4, PM2_supporting.