FBN1 and Marfan syndrome: The clinical diagnosis is based on the revised Ghent nosology.1 Heterozygous pathogenic variants in the FBN1 gene, encoding fibrillin-1, an extracellular matrix protein, are found in the majority of patients with MFS (1,850 different pathogenic variants described in the UMD-FBN1 database2 (http://www.umd.be/FBN1/).