TBX1 and 22q11.2 deletion syndrome: Interestingly, Tbx1 is believed to be the major mutated gene in DiGeorge syndrome, a human hereditary disease leading to mental retardation attributable to vascular malformations; Tbx1 has previously been described to be downstream of Wnt/β-catenin in non-endothelial cells (Huh and Ornitz 2010).