PAX9 polymorphisms and susceptibility to sporadic tooth agenesis: a case-control study in southeast China

Genetic study of non-syndromic tooth agenesis through the screening of paired box 9, msh homeobox 1, axin 2, and Wnt family member 10A genes: a case-series

Non-syndromic tooth agenesis (NSTA) is the most common developmental anomaly in humans. Several studies have been conducted on dental agenesis and numerous genes have been identified. However, the pathogenic mechanisms responsible for NSTA are not clearly understood. We studied a group of 28 patients with sporadic NSTA and nine patients with a family history of tooth agenesis. We focused on four genes - paired box 9 (PAX9), Wnt family member 10A (WNT10A), msh homeobox 1 (MSX1), and axin 2 (AXIN2) - using direct Sanger sequencing of the exons and intron-exon boundaries. The most prevalent variants identified in PAX9 and AXIN2 genes were analyzed using the chi-square test. The sequencing results revealed a number of variants in the AXIN2 gene, including one novel missense mutation in one patient with agenesis of a single second premolar. We also identified one variant in the AXIN2 gene as being a putative risk factor for tooth agenesis. Only one missense mutation was identified in the WNT10A gene and this mutation was found in two patients. Interestingly, WNT10A is reported as the most prevalent gene mutated in the European population with NSTA.

Functional Study of Ectodysplasin-A Mutations Causing Non-Syndromic Tooth Agenesis

Recent studies have demonstrated that ectodysplasin-A (EDA) mutations are associated with non-syndromic tooth agenesis. Indeed, we were the first to report three novel EDA mutations (A259E, R289C and R334H) in sporadic non-syndromic tooth agenesis. We studied the mechanism linking EDA mutations and non-syndromic tooth agenesis in human embryonic kidney 293T cells and mouse ameloblast-derived LS8 cells transfected with mutant isoforms of EDA. The receptor binding capability of the mutant EDA1 protein was impaired in comparison to wild-type EDA1. Although the non-syndromic tooth agenesis-causing EDA1 mutants possessed residual binding capability, the transcriptional activation of the receptor's downstream target, nuclear factor κB (NF-κB), was compromised. We also analyzed the changes of selected genes in other signaling pathways, such as WNT and BMP, after EDA mutation. We found that non-syndromic tooth agenesis-causing EDA1 mutant proteins upregulate BMP4 (bone morphogenetic protein 4) mRNA expression and downregulate WNT10A and WNT10B (wingless-type MMTV integration site family member 10A and 10B) mRNA expression. Our results indicated that non-syndromic tooth agenesis causing EDA mutations (A259E, R289C and R334H) were loss-of-function, and suggested that EDA may regulate the expression of WNT10A, WNT10B and BMP4 via NF-κB during tooth development. The results from our study may help to understand the molecular mechanism linking specific EDA mutations with non-syndromic tooth agenesis.

A Novel AXIN2 Missense Mutation Is Associated with Non-Syndromic Oligodontia

Oligodontia is defined as the congenital absence of six or more permanent teeth, excluding the third molars. Oligodontia may contribute to masticatory dysfunction, speech alteration, aesthetic problems and malocclusion. Numerous gene mutations have been association with oligodontia. In the present study, we identified a de novo AXIN2 missense mutation (c.314T>G) in a Chinese individual with non-syndromic oligodontia. This mutation results in the substitution of Val at residue 105 for Gly (p.Val105Gly); residue 105 is located in the highly conserved regulator of G protein signaling (RGS) domain of the AXIN2 protein. This is the first report indicating that a mutation in the RGS domain of AXIN2 is responsible for non-syndromic oligodontia. Our study supports the relationship between AXIN2 mutation and non-syndromic oligodontia and extends the mutation spectrum of the AXIN2 gene.

Irf6-Related Gene Regulatory Network Involved in Palate and Lip Development

Numerous genes including Irf6 have been revealed to contribute to cleft lip with or without cleft palate (CL/P). In this study, we performed a systematic bioinformatics analysis of Irf6-related gene regulatory network involved in palate and lip development by using GeneDecks, DAVID, STRING, and GeneMANIA database. Our results showed that many CL/P candidate genes have relation with Irf6, and 9 of these genes, including Msx1, Pvrl1, Pax9, Jag2, Irf6, Tgfb3, Rara, Gli2, and Tgfb2, were enriched into the CL/P gene group. Some of these 9 genes also were commonly involved in different signaling pathways and different biological processes, and they also have protein-protein interactions with Irf6. These findings make us analyze the intricate function of Irf6 in a CL/P gene regulatory network, followed by guiding us to perform further functional studies on these genes in the future. This method also offers us a simple, cheap, but useful method to analyze the relationship with a gene regulatory network of a certain disease such as CL/P.

A novel non-stop mutation in MSX1 causing autosomal dominant non-syndromic oligodontia

Oligodontia, which is the congenital absence of six or more permanent teeth, excluding the third molars, may contribute to masticatory dysfunction, speech alteration, aesthetic problems and malocclusion. Msh homeobox 1 (MSX1) was the first gene identified as causing non-syndromic oligodontia. In this study, we identified a novel heterozygous non-stop mutation (c.910_911dupTA, p.*304Tyrext*48) in MSX1 in a Chinese family with autosomal dominant non-syndromic oligodontia. This novel mutation substitutes the stop codon with a tyrosine residue, potentially adding 48 amino acids to the C-terminus of MSX1. Further in vitro study found that mutant MSX1 could be expressed but had lost its ability to enter the nucleus. This is the first report indicating that a non-stop mutation in MSX1 is responsible for oligodontia. This study broadens the mutation spectrum for MSX1 and provides a new way to clarify the mechanism of MSX1 in tooth agenesis.

Complex analysis of multiple single nucleotide polymorphisms as putative risk factors of tooth agenesis in the Hungarian population

OBJECTIVES

The role was studied of multiple single nucleotide polymorphisms in tooth agenesis in the Hungarian population using a complex approach.

METHODS

Eight SNPs, PAX9 -912 C/T, PAX9 -1031 A/G, MSX1 3755 A/G, FGFR1 T/C rs881301, IRF6 T/C rs764093, AXIN2-8150 A/G, AXIN2-8434 A/G and AXIN2-30224 C/T, were studied in 192 hypodontia and 17 oligodontia cases and in 260 healthy volunteers. Case-control analysis was performed to test both allelic and genotypic associations as well as associations at the level of haplotypes. Multivariate exploratory Bayesian network-based multi-level analysis of relevance (BN-BMLA) as well as logistic regression analysis were performed.

RESULTS

Conventional statistics showed that PAX9 SNP -912 C/T and the MSX1 SNP changed the incidence of hypodontia, although after Bonferroni correction for multiple hypothesis testing, the effects were only borderline tendencies. Using a statistical analysis better suited for handling multiple hypotheses, the BN-BMLA, PAX9 SNPs clearly showed a synergistic effect. This was confirmed by other multivariate analyses and it remained significant after corrections for multiple hypothesis testing (p < 0.0025). The PAX9-1031-A-PAX9-912-T haplotype was the most relevant combination causing hypodontia. Interaction was weaker between PAX9 and MSX1, while other SNPs had no joint effect on hypodontia.

CONCLUSION

This complex analysis shows the important role of PAX9 and MSX1 SNPs and of their interactions in tooth agenesis, while IRF6, FGFR1 and AXIN2 SNPs had no detectable role in the Hungarian population. These results also reveal that risk factors in hypodontia need to be identified in various populations, since there is considerable variability among them.

PAX9 polymorphism and susceptibility to sporadic non-syndromic severe anodontia: a case-control study in southwest China

Our research aimed to look into the clinical traits and genetic mutations in sporadic non-syndromic anodontia and to gain insight into the role of mutations of PAX9, MSX1, AXIN2 and EDA in anodontia phenotypes, especially for the PAX9.

PAX9 polymorphisms and susceptibility with sporadic tooth agenesis in Turkish populations: a case-control study

Background

Hypodontia, the congenital absence of one or a few teeth is one of the most common alterations of the human dentition. Familial hypodontia is caused by mutations in PAX9, Msx1 and Axin2 genes. Limited numbers of studies are present to show etiological factors beyond this anomaly in Turkish community belonging to Caucasian racial family. The purpose of this study is to investigate the relationships between the two different single nucleotide polymorphisms that are G-1031A and T-912C with hypodontia in Caucasians.

200 individuals having hypodontia and 114 normal individuals having all 32 teeth present were selected for the study. Blood samples were collected from each individual and DNA was extracted. To determine the polymorphisms, PCR-RFLP method was used.

Results

The outcomes suggest that the individuals having AC haplotype carry less risk in having hypodontia compared with the rest of the haplotype groups (OR = 3.88; CI = 95%; p = 0.001). The ratio of GT haplotype is less in the hypodontia group meaning that the GT carriers are in risk group in terms of hypodontia risk.

Conclusion

These results indicate that polymorphisms in the promoter region of PAX9 gene may have an influence on the transcriptional factors and activity of this gene and are associated with hypodontia in Caucasian individuals.

Sequence analysis of PAX9, MSX1 and AXIN2 genes in a Chinese oligodontia family

OBJECTIVES

The goal of our research was to look into the clinical traits and genetic mutations in nonsyndromic oligodontia in a Chinese family and to gain insight into the role of mutations of PAX9, MSX1 and AXIN2 in oligodontia phenotypes.

MATERIALS AND METHODS

6 subjects from a family underwent complete oral examination, including panoramic radiographs. Retrospective data were reviewed and blood samples were collected. PCR primers for PAX9, MSX1, and AXIN2 were designed through the Oligo Primer Analysis Software. PCR products were purified and sequenced using the BigDye Terminator Kit and analysed by the 3730 DNA Analyzer.

RESULTS

The proband missed 4 permanent canines, 2 permanent maxillary lateral incisors, 2 permanent mandibular lateral incisors, and 2 permanent mandibular central incisors, whilst his maternal grandfather lacked only 2 permanent mandibular central incisors. Moreover, the size of some permanent teeth appeared smaller than normal values of crown width of Chinese people. Oligodontia and abnormalities of teeth were not present in other family members. Radiographic examination showed that the proband and the rest of family members retained all germs of the third molars. There was one known mutation A240P (rs4904210) of PAX9 in the coding region in the proband and the maternal family members (II-2, II-3, and II-4), which possibly contributed to structural and functional changes of proteins. No mutations were identified in MSX1 and AXIN2.

CONCLUSIONS

Our findings may imply that the PAX9 A240P mutation is a risk factor for oligodontia in the Chinese population. A240P is likely to be a genetic cause of oligodontia though previous literature suggested it as a polymorphism only.

Genetic variation among major human geographic groups supports a peculiar evolutionary trend in PAX9

A total of 172 persons from nine South Amerindian, three African and one Eskimo populations were studied in relation to the Paired box gene 9 (PAX9) exon 3 (138 base pairs) as well as its 5'and 3'flanking intronic segments (232 bp and 220 bp, respectively) and integrated with the information available for the same genetic region from individuals of different geographical origins. Nine mutations were scored in exon 3 and six in its flanking regions; four of them are new South American tribe-specific singletons. Exon3 nucleotide diversity is several orders of magnitude higher than its intronic regions. Additionally, a set of variants in the PAX9 and 101 other genes related with dentition can define at least some dental morphological differences between Sub-Saharan Africans and non-Africans, probably associated with adaptations after the modern human exodus from Africa. Exon 3 of PAX9 could be a good molecular example of how evolvability works.

Mutations in the PAX9 gene in sporadic oligodontia

OBJECTIVES

Oligodontia, a congenital lack of six or more teeth, is often associated with mutations in the PAX9 gene; therefore, we searched for mutations in this gene.

DESIGN

In the present work, we sequenced fragments of the PAX9 gene in individuals with sporadic oligodontia. Next, we genotyped some mutations we found in patients with oligodontia and individuals without tooth agenesis.

SETTING AND SAMPLE POPULATION

DNA sequencing was performed in the material isolated from peripheral blood lymphocytes of six unrelated patients with sporadic, non-syndromic oligodontia. These patients were selected based upon explorative cluster analysis. Genotyping was performed in 38 patients with oligodontia and 100 control individuals.

MATERIAL AND METHODS

Direct sequencing and restriction fragment length polymorphism PCR were employed.

RESULTS

We detected two homozygotic substitutions, IVS2-109G>C and IVS2-54A>G, in intron 2 in three patients. Another homozygotic substitution in intron 2, IVS2-41A>G, was revealed in two patients. Two patients had an IVS3+40G>A homozygotic change in intron 3 and 4 patients displayed a 717C>T transition in exon 4 (silent mutation). One patient had a heterozygotic 718G>C transversion, resulting in a missense Ala240Pro substitution. We detected also several other intronic substitutions. Further genotyping of the IVS2-54A>G, IVS2-109G>C, and IVS2-41A>G mutations suggested that they can display polymorphic changes.

CONCLUSION

The IVS2-54A>G, IVS2-109G>C, and IVS2-41A>G mutations of the PAX9 gene may represent polymorphism associated with sporadic oligodontia.

Craniofacial profile in Southern Chinese with hypodontia

The association between craniofacial morphology and congenitally missing teeth is at present unclear. The aims of this study were to investigate whether hypodontia is associated with changes in the sagittal skeletal profile and to identify putative relationships between the skeletal profile and the severity of hypodontia. In a cross-sectional analytical study, the craniofacial structure and profile based on two-dimensional lateral cephalograms of Southern Chinese hypodontia patients (n = 49, 24 males, 25 females, mean age 16.4 years) and a comparison group without hypodontia (n = 41, 15 males, 26 females, mean age 16.7 years) were compared. The hypodontia patients were divided into three subgroups according to the severity of hypodontia (mild: < or =5, moderate: 6-9, and severe: > or =10 congenitally missing permanent teeth). All hypodontia patients had a significantly reduced mandibular plane, ANB, and face height compared with the control group (P < 0.05). A significant increase in chin thickness was also observed in the hypodontia patients (P < 0.05). As the severity of hypodontia increased from moderate to severe, a tendency to develop a retrognathic maxilla and a Class III skeletal relationship was noted in addition to the above features, making the already thick chin even more prominent. Statistically significant correlations (Pearson's correlation coefficient) were found between the number of missing teeth and SNA, NAFH, and ANB angles, the mandibular plane, chin thickness, and face height. In Southern Chinese subjects, hypodontia was associated with a shorter face, a flatter mandibular plane, a more pronounced chin, and a Class III skeletal profile. In severe hypodontia subjects, the maxilla was more retrognathic with a greater predilection to a Class III skeletal relationship.