While these phenotypic findings are in accordance with the B3GAT3 associated-clinical phenotype described in the literature,26–29 this is to our knowledge the first description of a microdeletion in the region causing developmental and cardiovascular disease, although a 9.86 Mb duplication encompassing B3GAT3 (and incidentally KDM2A, a candidate identified in this study) has been described in a DECIPHER participant (333571) with mitral valve prolapse, developmental delay, and other ECAs. The gene discussed is B3GAT3; the disease is mitral valve prolapse.