Greig syndrome, and its more severe form known as acrocallosal syndrome, is associated primarily with loss-of-function heterozygous mutations of GLI3. Its symptoms resemble those of Gli3 heterozygous mice (Gli3XtJ, the extra-toes mouse) and suggest that, as in mice, Gli3 is haploinsufficient in humans [244]. This evidence concerns the gene GLI3 and acrocallosal syndrome.