ovarian cancer (EOC). The study shows that women with EOC are 8.1 times more likely to have hypodontia than are women without EOC. The suggestion therefore is that hypodontia can serve as a "marker" for potential risk of EOC in women. Genetics Genetic causes also involve the genes MSX1 and PAX9. Genetic associations for selective tooth agenesis ("STHAG") include: Failure of tooth formation due to disturbances during the early stages of development could be the cause of congenital missing teeth; this is also known as tooth agenesis. A variety of studies show that missing teeth are commonly associated with genetic and environmental factors. Some literature also shows that a combination of both factors may contribute to the occurrence of hypodontia. Most craniofacial characteristics are influenced by both genetic and environmental factors through complex interactions. The variable expressivity of traits can be either completely genetically determined, environmentally determined, or both. That genetics plays an important role in hypodontia is shown in many different cases. There are hundreds of genes expressed and involved in regulating tooth morphogenesis. Although a single gene defect may contribute to hypodontia, more studies propose that hypodontia is the result of one or more points of closely linked genetic mutations, or polygenic defects. The pattern of congenitally missing teeth seen in monozygotic twins is different, suggesting an underlying epigenetic factor, which may be due to the simultaneous occurrence of two anomalies. This multifactorial aetiology involves environmental factors which trigger the genetic anomalies, resulting in the occurrence of dental agenesis. Common environmental factors include infection, trauma and drugs which predispose to the condition. In hereditary cases, evidence of dental germ developing after surrounding tissues have closed the space required for development may be a large contributing factor, as well as such genetic disorders as Down syndrome, ectodermal dysplasia, cleidocranial dysplasia, and cleft lip and cleft palate. MSX1 MSX1 (muscle segment homeobox 1) is involved in condensation of ectomesenchyme in the tooth germ. Among the members of homeobox genes, MSX1 and MSX2 are crucial in mediating direct epithelial-mesenchymal interactions during tooth development by expressing in regions of condensing ectomesenchyme in the tooth germ. MSX1 mutations have been identified as a contributing factor in missing second premolars, third molars, and a small percentage of first molars. MSX1 is less likely to cause anterior agenesis. Heterozygous mutations in PAX9 (paired box gene 9) could arrest tooth morphogenesis as it plays a role