This syndrome is associated with the gene Claudin 5 CLDN5 [28]; as might be expected, we find many patients with phenotypes corresponding to this cluster show mutations in this gene, however, we also notice patients with other genes from this family, particularly CLDN15 and CLDN23. In fact, previous work examining CNVs in patients with congenital heart malformations found CLDN23 amongst other genes affected in three separate patients with distinct types of malformations: hypoplastic left heart syndrome, ventricular septal defect and complete atrioventricular canal. Here, CLDN23 is linked to ventricular septal defect 1.