Since considerable phenotypic variation is found in the reduced lateral incisor, Saracatinib clinical trial tooth shapes within MZ co-twins can be very similar or quite different, as Saheki [19] noted. Table 3 shows the frequency of reduced maxillary lateral incisors when considering all four teeth in both members of a twin pair. All four teeth showed the reduced type more frequently in MZ twin pairs than in DZ twin pairs (P < 0.05). Discordance of reduced tooth form in the maxillary lateral incisor between co-twins of MZ pairs has been discussed from genetic, epigenetic and environmental perspectives. In this paper we consider two hypotheses:

(1) environmental factors influencing tooth formation, and (2) phenotypic variation caused by epigenetic influences. Townsend et al. [20] have discussed discordance between MZ co-twins due to differences in their embryonic environment. Monochorionic twins are MZ twins who share the same placenta and chorionic membrane during prenatal development. Although the twins have a common placenta, their blood supply is usually well-balanced [21]. However, in 5–15% of monochorionic pregnancies, twin transfusion syndrome associated with anterio-venous anastomoses, can lead to one member of a this website twin pair receiving better nourishment than the other. Differences in blood flow to developing tooth germs at critical

stages of their formation, resulting in nutritional discrepancies, could presumably also influence the resultant dental phenotypes. This could lead to one member having well-developed lateral incisors, but the other having less-developed lateral incisors.

For example, uptake CYTH4 of glucose into dental epithelial and mesenchymal cells, mediated by glucose transporters, has been shown to play an important role in early dental development and subsequent determination of tooth size in mice [22]. Townsend et al. [23] noted that there was evidence of one missing maxillary lateral incisor or mandibular second premolar in 24 of the 278 MZ twin pairs who they examined, with 21 of these pairs showing discordant expression (87.5%). By focusing on the differences between MZ co-twins rather than their similarities, they postulated that epigenetic events during odontogenesis might account for the distinct differences between members of MZ twin pairs. Epigenetics refers to heritable changes in gene activity that are not caused by changes in the DNA sequence [24] and [25]. Variation due to genetic influences is classically based on changes to the DNA sequence (the genotype), but alterations in gene expression or alterations in the nature of cellular interactions at a local tissue level, both of which can be referred to as epigenetic factors, have other causes. The science of epigenetics includes the many regulatory systems of the body involving DNA methylation and histone modification.