 Mutations in this gene, which was once known as homeobox 7, have also been associated with Witkop syndrome, Wolf-Hirschhorn syndrome, and autosomal dominant hypodontia.Haploinsufficiency of MSX1 protein affects the development of all teeth, preferentially third molars and second premolars.The effect of haploinsufficiency of PAX9 on the development of incisors and premolars is probably caused by a deficiency of MSX1 protein.