The clinical significance and correlative signaling pathways of paired box gene 9 in development and carcinogenesis

Paired box 9 (PAX9) gene belongs to the PAX family, which encodes a family of metazoan transcription factors documented by a conserved DNA binding paired domain 128-amino-acids, critically essential for physiology and development. It is primarily expressed in embryonic tissues, such as the pharyngeal pouch endoderm, somites, neural crest-derived mesenchyme, and distal limb buds. PAX9 plays a vital role in craniofacial development by maintaining the odontogenic potential, mutations, and polymorphisms associated with the risk of tooth agenesis, hypodontia, and crown size in dentition. The loss-of-function of PAX9 in the murine model resulted in a short life span due to the arrest of cleft palate formation and skeletal abnormalities. According to recent studies, the PAX9 gene has a significant role in maintaining squamous cell differentiation, odontoblast differentiation of pluripotent stem cells, deregulation of which is associated with tumor initiation, and malignant transformation. Moreover, PAX9 contributes to promoter hypermethylation and alcohol- induced oro-esophageal squamous cell carcinoma mediated by downregulation of differentiation and apoptosis. Likewise, PAX9 activation is also reported to be associated with drug sensitivity. In summary, this current review aims to understand PAX9 function in the regulation of development, differentiation, and carcinogenesis, along with the underlying signaling pathways for possible cancer therapeutics.

A review on non-syndromic tooth agenesis associated with PAX9 mutations

Tooth agenesis in the reduction of tooth number which includes hypodontia, oligodontia and anodontia is caused by disturbances and gene mutations that occur during odontogenesis. To date, several genetic mutations that unlock the causes of non-syndromic tooth agenesis are being discovered; these have been associated with certain illnesses because tooth development involves the interaction of several genes for tooth epithelium and mesenchyme odontogenesis. Mutation of candidate genes PAX9 and MSX1 have been identified as the main causes of hypodontia and oligodontia; meanwhile, AXIN2 mutation is associated with anodontia. Previous study using animal models reported that PAX9-deficient knockout mice exhibit missing molars due to an arrest of tooth development at the bud stage. PAX9 frameshift, missense and nonsense mutations are reported to be responsible; however, the most severe condition showed by the phenotype is caused by haploinsufficiency. This suggests that PAX9 is dosage-sensitive. Understanding the mechanism of genetic mutations will benefit clinicians and human geneticists in future alternative treatment investigations.

Prevalence of isolated maxillary lateral incisor agenesis in Syrian adolescents

PURPOSE

This research is designed to obtain a better understanding and provide more insight of this phenomenon through evaluating the prevalence of congenital absence of maxillary lateral incisors in a Syrian population.

METHODS

The method involved clinical examination of 8000 school children with an equal number of males and females (age range 12-15 years) to identify students only affected by bilateral or unilateral congenital absence of maxillary lateral incisors. Agenesis was determined based on radiological evidence.

RESULTS

The results of this study showed that the prevalence of isolated maxillary lateral incisors agenesis was 1.15%. In the sample studied, 66.3% of the patients were female and 33.7% were male (p < 0.05). Absence was bilateral in 47.8% of patients and unilateral in 52.2%. Of the unilateral cases, 48% occurred on the right side and 52% on the left side, and the contralateral maxillary incisor was found to be microdont in 43.75%, right lateral in 47.6%, and left lateral in 52.4%.

CONCLUSION

The results of this study allow the conclusion that the prevalence of isolated maxillary lateral incisors agenesis in a Syrian population is within the average range with regard to other populations. A significant familial component to the etiology of maxillary lateral incisors agenesis was found.

Study of alveolar ridge dimensions before and after orthodontic treatment in maxillary lateral incisor agenesis: A pilot study

The objective of this study was to compare the dimensional changes in the alveolar ridge before, at the end of, and one year after orthodontic treatment in cases of Maxillary Lateral Incisor Agenesis and the possibility of using plaster models and panoramic radiographs as substitutes for cone beam-computed tomography.

MATERIAL AND METHODS

A total of 228 measurements were performed on plaster models and panoramic radiographs: before (T1), at the end of (T2), and 1 year after orthodontic treatment (T3). At stage T2, the cone beam-computed tomography was also analyzed. Non-parametric tests were used.

RESULTS

In all 3 stages, there was no statistically significant difference regarding the thickness of the models, the height of the bone in the panoramic radiographs, the space opening and the height of the bone in the panoramic radiographs, or the space opening in the models and the thickness in the same plaster models. However, a statistically significant difference was observed for the width in the panoramic radiograph during all 3 stages. Cone beam-computed tomography did not reveal a statistically significant correlation regarding the height and width of the bone compared with the panoramic radiographs, and the thickness as compared with plaster models.

CONCLUSION

There was no significant variation in thickness, height and width of the bone over time. It was demonstrated that plaster models and panoramic radiographs do not appear to be good substitutes for cone beam-computed tomography for these specific measurements.

Identification of Genetic Risk Factors for Maxillary Lateral Incisor Agenesis

Tooth agenesis affects 20% of the world population, and maxillary lateral incisors agenesis (MLIA) is one of the most frequent subtypes, characterized by the absence of formation of deciduous or permanent lateral incisors. Odontogenesis is a complex mechanism regulated by sequential and reciprocal epithelial-mesenchymal interactions, controlled by activators and inhibitors involved in several pathways. Disturbances in these signaling cascades can lead to abnormalities in odontogenesis, resulting in alterations in the formation of the normal teeth number. Our aim was to study a large number of genes encoding either transcription factors or key components in signaling pathways shown to be involved in tooth odontogenesis. We selected 8 genes— MSX1, PAX9, AXIN2, EDA, SPRY2, TGFA, SPRY4, and WNT10A—and performed one of the largest case-control studies taking into account the number of genes and variants assessed, aiming at the identification of MLIA susceptibility factors. We show the involvement of PAX9, EDA, SPRY2, SPRY4, and WNT10A as risk factors for MLIA. Additionally, we uncovered 3 strong synergistic interactions between MLIA liability and MSX1- TGFA, AXIN2- TGFA, and SPRY2- SPRY4 gene pairs. We report the first evidence of the involvement of sprouty genes in MLIA susceptibility. This large study results in a better understanding of the genetic components and mechanisms underlying this trait.

Earliest evidence for social endogamy in the 9,000-year-old-population of Basta, Jordan

The transition from mobile to sedentary life was one of the greatest social challenges of the human past. Yet little is known about the impact of this fundamental change on social interactions amongst early Neolithic communities, which are best recorded in the Near East. The importance of social processes associated with these economic and ecological changes has long been underestimated. However, ethnographic observations demonstrate that generalized reciprocity – such as open access to resources and land – had to be reduced to a circumscribed group before regular farming and herding could be successfully established. Our aim was thus to investigate the role of familial relationships as one possible factor within this process of segregation as recorded directly in the skeletal remains, rather than based on hypothetical correlations such as house types and social units. Here we present the revealing results of the systematically recorded epigenetic characteristics of teeth and skulls of the late Pre-Pottery Neolithic community of Basta in Southern Jordan (Figure S1). Additionally, mobility was reconstructed via a systematic strontium (Sr) isotope analysis of tooth enamel of the Basta individuals. The frequency of congenitally missing maxillary lateral incisors in the 9,000-year-old community of Basta is exceptionally high (35.7%). Genetic studies and a worldwide comparison of the general rate of this dental anomaly in modern and historic populations show that the enhanced frequency can only be explained by close familial relationships akin to endogamy. This is supported by strontium isotope analyses of teeth, indicating a local origin of almost all investigated individuals. Yet, the accompanying archaeological finds document far-reaching economic exchange with neighboring groups and a population density hitherto unparalleled. We thus conclude that endogamy in the early Neolithic village of Basta was not due to geographic isolation or a lack of exogamous mating partners but a socio-cultural choice.

Associations between the risk of tooth agenesis and single-nucleotide polymorphisms of MSX1 and PAX9 genes in nonsyndromic cleft patients

OBJECTIVE

To investigate the association between the risk of tooth agenesis and single-nucleotide polymorphisms (SNPs) of MSX1 and PAX9 genes in nonsyndromic cleft patients.

MATERIALS AND METHODS

The subjects were 126 Korean nonsyndromic cleft patients. Tooth agenesis type (TAT) was classified as none (0); cleft area (1); cleft area + other area (2); and other area (3) based on agenesis of the maxillary lateral incisor (MXLI) and another tooth within or outside the cleft area. TAT was further grouped into two subcategories (0 and 1) and four subcategories (0, 1, 2, and 3). Three SNPs of MSX1 and 10 SNPs of PAX9 were investigated using Fisher's exact test and logistic regression analysis.

RESULTS

Although the association between genotype distribution of PAX9-rs7142363 and TAT was significant (P < .05 in four subcategories), genotypic odds ratios (GORs) of SNPs in each TAT were not meaningful. However, for MSX1-rs12532 and PAX9-rs2073247, associations between genotypic distribution and TAT were significant (P < .01 in four subcategories and P < .05 in two subcategories; P < .01 in two subcategories, respectively). In cleft area, GORs of MXLI agenesis in genotypes GA of MSX1-rs12532 and CT of PAX9-rs2073247 were increased by 3.14-fold and 4.15-fold compared with genotype GG of MSX1-rs12532 and CC of PAX9-rs2073247, respectively (P <. 01; P < .05). In cleft area + other area, the GOR of agenesis of MXLI and another tooth in genotype AA of MSX1-rs12532 was increased by fivefold compared with genotype GG (P < .05).

CONCLUSION

Genetic disturbances of MSX1 and PAX9 genes are associated with tooth agenesis within and outside the cleft area.

Dentistry and molecular biology: a promising field for tooth agenesis management

Tooth agenesis is the failure of tooth bud development, causing definitive absence of the tooth. It is the most common dental anomaly, affecting up to one-quarter of the general population. The main cause is related to abnormal function of specific genes which play key roles during odontogenesis, particularly MSX1 and PAX9. MSX1 is a transcription factor highly expressed in the mesenchyme of developing tooth germs, whereas PAX9 is a transcription factor that shows a direct relationship with craniofacial development, particularly the formation of the palate and teeth. Despite the high frequency of tooth agenesis, there are as yet only a restricted number of mutations in MSX1 and PAX9 that have been associated with non-syndromic tooth agenesis. Thus, a deeper analysis of the gene networks underlying this anomaly is imperative. By means of a literature review based on Medline, PubMed, Lilacs, NCBI, and STRING, performed between 1991 and 2010 and focused on etiologically associated mutations, this work aimed to assess the latest advances in the genetic etiology of tooth agenesis and to offer an insight into how they can assist dental practice in the near future. A better knowledge of the genetic networks underlying tooth agenesis will lead to better treatment options and, perhaps, a tool for early diagnosis possibly related to DNA examination based on polymorphic variants. Such a test based on DNA analysis may be available to and accessible by clinicians, resulting in a more accurate diagnosis and allowing for a better approach to this anomaly.

Polymorphism in the MSX1 gene in a family with upper lateral incisor agenesis

OBJECTIVE

The MSX1 gene plays a key role in odontogenesis regulation, particularly during early stages. Since only a few genetic variants have thus far been associated with non-syndromic tooth agenesis, we screened for mutations in this gene, aiming to detect a relationship between genotype and phenotype.

DESIGN

The sample consisted of one proband with non-syndromic hypodontia involving upper lateral incisors, three relatives and ten unaffected controls. The proband and two affected relatives showed the same phenotype. DNA was extracted from buccal epithelial cells, and direct sequencing was performed. The two exons of MSX1 were first sequenced in the proband. When an alteration was detected, his relatives were investigated by the same method.

RESULTS

We identified the known polymorphism *6C>T in the homozygous state in all three affected family members. The unaffected father was heterozygous and ten control samples were negative for the *6C>T polymorphism.

CONCLUSIONS

The *6C>T polymorphism, when homozygous, may contribute to agenesis of upper lateral incisors. However, since the *6C>T polymorphism is quite common, additional genes must be involved in this phenotype.

Tooth agenesis in a Portuguese population

OBJECTIVE

The aim of this retrospective study was to evaluate the prevalence and pattern of hypodontia in the permanent dentition, including and excluding third molars, in a Portuguese sample.

PATIENTS AND METHODS

The study group comprised 2888 patients, observed between 2005 and 2009 at the Dentistry Clinic of the Instituto Superior de Ciências de Saúde-Norte (ISCSN, Portugal). The patients were examined for evidence of hypodontia and presence or absence of deciduous teeth in those presenting agenesis. The age range varied from 7 to 21 years. In order to study the absence of the third molar, subjects under 14 years were excluded. Statistical analysis was performed using SPSS(®).

RESULTS

Excluding third molars, the prevalence of tooth agenesis was 6.1% for the Portuguese population. Tooth agenesis was found more frequently in females than in males, although this difference was not statistically significant (P>.05). The most commonly missing tooth was the mandibular second premolar, followed by maxillary lateral incisor, and maxillary second premolar. There was a significantly higher prevalence of missing third molars in the agenesis group than in the non-agenesis group. There was a correlation between second premolar and upper lateral agenesis with presence of their corresponding deciduous teeth.

CONCLUSIONS

The prevalence of tooth agenesis was found to be 6.1% for this Portuguese population and there was a correlation between agenesis and presence of deciduous teeth and between agenesis and missing third molars.

Craniofacial repercussions in maxillary lateral incisors agenesis

OBJECTIVES

Assessment of the influence of maxillary lateral incisor agenesis (MLIA) on the facial morphogenesis.

METHODS

Evaluation of the skeletal dimensions of the upper maxilla and its incisor region. Analysis was performed among three groups: individuals with MLIA, its relatives and the normal population. Among these a comparison between adults and growing individuals was performed.

RESULTS

MLIA may interfere with the maxillary length and the anterosuperior facial height, negatively conditioning on its potential growth. MLIA was not correlated with changes of the palatine plane inclination, maxillary height nor with adjustment of the anterior nasal spine dimensions related to the Frankfurt plan or to the posterior nasal spine-Frankfurt plan during the observed development stage; the backward angle of the incisors in children with bilateral agenesis of lateral incisors appear to have been corrected in adulthood.

CONCLUSIONS

MLIA is associated with an upper maxilla shortening, and appear to interfere significantly with the anterior facial height, reducing its potential size.

Dental repercussions of maxillary lateral incisor agenesis

The aim of this study was to assess the influence of maxillary lateral incisor agenesis (MLIA) on the position of other teeth in the dental arch. The sample consisted of 147 individuals (66 males and 81 females) divided into two age groups: a growth phase group (A) comprising 43 individuals (18 males and 25 females, ages ranging from 9 to 16 years) and an adult group (B) (with females older than 14 and males older than 18 years) comprising 104 individuals (48 males and 56 females, ages ranging from 15 to 45 years). Within these groups, the individuals were then divided into three subsets: group 1 with MLIA, group 2 relatives of group 1 but without MLIA, and group 3 individuals from the general population (without agenesis and unrelated). Clinical evaluation of the maxillary dental midline and of the antero-posterior relationship between the upper and lower arches at the first permanent molars and canines was performed. Variables were compared by a chi-square test. There was a significant (P < 0.05) clinical association between the presence of MLIA (more often unilateral) and the deviation of the maxillary dental midline. MLIA was associated with a Class II malocclusion; this was more frequent on the same side as the agenesis.