Homozygous Tbx1 mutant mice (Jerome and Papaioannou, 2001; Merscher et al., 2001) and tbx1 mutant zebrafish (van gogh, vgo) (Piotrowski et al., 2003) recapitulate the major structural defects observed in patients with severe DiGeorge syndrome, including heart, thymus and craniofacial defects (Table 3), but do not recapitulate all aspects of human DiGeorge syndrome. Here, TBX1 is linked to 22q11.2 deletion syndrome.