Genes associated with coloboma phenotypes have been identified in at least 20 syndromes, where the coloboma arises as an occasional feature of a complex multisystem birth defect (9,13–17); these include dominant mutations in SHH (OMIM 600725) (18), RAX (OMIM 601881) (19), GDF3 (OMIM 606522) and GDF6 (OMIM 601147) (13,20) and recessive mutations in STRA6 (OMIM 610745) (21) and SMOC1 (OMIM 608488) (22). This evidence concerns the gene RAX and coloboma.