Nine Novel PAX9 Mutations and a Distinct Tooth Agenesis Genotype-Phenotype

Genetic and phenotypic heterogeneity of tooth agenesis: An update including candidate genes

OBJECTIVE

This study aims to further investigate the genetic etiology as well as the corresponding characteristics of tooth agenesis (TA). It focuses on expanding the gene spectrum and exploring genotype-phenotype correlations and potential candidate genes for TA.

DESIGN

The narrative review approach was conducted, providing a comprehensive perspective of tooth agenesis-related literature.

RESULTS

We describe the (candidate) causal genes of syndromic TA and nonsyndromic TA respectively. There is overlap between the gene spectrum of the two forms. Tooth phenotypes (either the number of missing teeth or the malformations) of syndromic form are more severe than that of nonsyndromic form. The phenomenon even exists among family members carried the same variant, highlighting the disorder's complexity and the causal genes' expression variability. Besides, the candidate genes, corresponding functional and case evidence are updated, which contributes to improve the diagnosis of TA.

CONCLUSIONS

TA is a group of complex disorder regulated by multiple genetic signaling pathways. We review the previously known and novel found genes/candidate genes related to TA, emphasizing the genetic and phenotypic heterogeneity. The enlarged spectrum is useful for further promoting the understanding of TA and early diagnosis. It is suggested that molecular diagnosis is particularly vital for early management and genetic counseling.

Identification and functional study of a novel variant of PAX9 causing tooth agenesis

OBJECTIVES

To search for pathogenic gene of a family with non-syndromic tooth agenesis, and explore the possible pathogenesis.

MATERIALS AND METHODS

A Chinese family with non-syndromic tooth agenesis was recruited and screened for the pathogenic variants by whole exome sequencing technology and co-segregation analysis. The subcellular localization of wild-type and mutant protein was detected by immunofluorescence assay. Cycloheximide chase assay was performed to examine the difference in degradation rate between mutant protein and wild-type one. Dual-luciferase reporter assays were conducted to explore the alterations of mutant protein in the regulation of downstream target genes.

RESULTS

A novel missense variant of PAX9 (c.296C>A:p.A99D) was found in this family. Bioinformatics software showed β-return and the random coil were shortened in the p.A99D. The variant did not affect the subcellular localization of PAX9, but the degradation rate of p.A99D was accelerated (p < 0.05). p.A99D inhibited the activation of downstream target gene BMP4 (p < 0.05).

CONCLUSIONS

This novel variant expands the pathogenic gene spectrum. The variant impaired the protein structure, accelerated the degradation of protein, and inhibited the activation of the downstream target gene BMP4, an upstream molecule in the TGF-β/BMP pathway, which may contribute to tooth agenesis in this family.

A novel PAX9 variant in a Chinese family with non-syndromic oligodontia and genotype-phenotype analysis of PAX9variants

OBJECTIVES

This study aimed to identifyPAX9variants in non-syndromic tooth agenesis families of China, as well as to analyze the genotype⁃phenotype of non-syndromic tooth agenesis caused by PAX9variants, which can provide a basis for the genetic diagnosis of tooth agenesis.

METHODS

We collected the data of 44 patients with non-syndromic oligodontia who underwent treatment at Stomatological Hospital of Hebei Medical University between 2018 and 2023. Whole-exome sequencing was performed on the peripheral blood of the proband and its core family members, and the variants were verified by Sanger sequencing. Pathogenicity analysis and function prediction of the variants were performed using bioinformatics tools. The correlation between the genotype of PAX9 variant and its corresponding phenotype was examined by reviewing 55 publications retrieved from PubMed. The studies involved 232 tooth agenesis patients with PAX9 variants.

RESULTS

A novel PAX9 c.447delG (p.Pro150Argfs*62) and a reported PAX9 c.406C>T (p.Gln136*) were identified in two Chinese families. Through bioinformatics analysis and three-dimensional structural modeling, we postulated that the frameshift variant was pathogenic. The outcome was the premature cessation of PAX9 protein, which caused severe structural and functional deficiencies. Summarizing the PAX9 genotype-phenotype relationship revealed that patients carrying the PAX9 variant commonly led to loss of the second molars.

CONCLUSIONS

We identified the novel PAX9 c.447delG (p.Pro150Argfs*62) in a Chinese family of non-syndromic oligodontia, expanding the known variant spectrum of PAX9. The most susceptible tooth position for PAX9 variants of tooth agenesis was the second molars and the deciduous molars during the deciduous dentition.

EDA Variants Are Responsible for Approximately 90% of Deciduous Tooth Agenesis

Deciduous tooth agenesis is a severe craniofacial developmental defect because it affects masticatory function from infancy and may result in delayed growth and development. Here, we aimed to identify the crucial pathogenic genes and clinical features of patients with deciduous tooth agenesis. We recruited 84 patients with severe deciduous tooth agenesis. Whole-exome and Sanger sequencing were used to identify the causative variants. Phenotype-genotype correlation analysis was conducted. We identified 54 different variants in 8 genes in 84 patients, including EDA (73, 86.9%), PAX9 (2, 2.4%), LRP6 (2, 2.4%), MSX1 (2, 2.4%), BMP4 (1, 1.2%), WNT10A (1, 1.2%), PITX2 (1, 1.2%), and EDARADD (1, 1.2%). Variants in ectodysplasin A (EDA) accounted for 86.9% of patients with deciduous tooth agenesis. Patients with the EDA variants had an average of 15.4 missing deciduous teeth. Mandibular deciduous central incisors had the highest missing rate (100%), followed by maxillary deciduous lateral incisors (98.8%) and mandibular deciduous lateral incisors (97.7%). Our results indicated that EDA gene variants are major pathogenic factors for deciduous tooth agenesis, and EDA is specifically required for deciduous tooth development. The results provide guidance for clinical diagnosis and genetic counseling of deciduous tooth agenesis.

Investigation of the fungiform papillae number in children with tooth number anomalies

OBJECTIVE

This cross-sectional study investigated the association between fungiform papillae (FP) numbers and tooth number anomalies in children, considering variables related to hypodontia and hyperdontia. The aim was to explore this association while adjusting for age and sex differences.

MATERIALS AND METHODS

A total of 144 children (aged 8-10) were categorized into hypodontia (n = 48), hyperdontia (n = 48), and control groups (n = 48). Clinical and radiographic diagnoses were used to classify tooth number anomalies. Hypodontia was categorized by number and location, while hyperdontia was categorized by number, shape, and location. FP were assessed using the Denver Papillae Protocol. Data analyses were performed using NCSS software, with p < 0.05 considered statistically significant.

RESULTS

The hypodontia group (22.5 ± 8.4) exhibited significantly lower FP than the control group (30.4 ± 9.2) and the hyperdontia group (27.9 ± 7.8) (p < 0.0005, p = 0.003, respectively). No significant difference existed between the hyperdontia and control groups. FP numbers in hypodontia subgroups showed no significant differences based on teeth agenesis numbers or locations. Similarly, hyperdontia subgroup analyses revealed no significant differences in FP numbers based on supernumerary teeth shapes (supplemental, conical, tuberculoid, paramolar) or the numbers of supernumerary teeth.

CONCLUSIONS

The lower FP numbers in children with hypodontia suggested an association between teeth and FP number. However, the non-significant difference in FP numbers with hyperdontia underscored the complexity of tooth development, warranting further investigations.

CLINICAL RELEVANCE

Children with hypodontia may exhibit distinct FP numbers compared to those without tooth number anomalies.

"Examining the link between tooth agenesis and papillary thyroid cancer: is there a risk factor?" Observational study

BACKGROUND

Mutations in one or multiple genes can lead to hypodontia and its characteristic features. Numerous studies have shown a strong genetic influence on the occurrence of hypodontia, and identified several genes, including AXIN2, EDA, FGF3, FGFR2, FGFR10, WNT10A, MSX1, and PAX9, that are directly associated with dental agenesis and carcinogenesis. The objective of this study was to investigate the occurrence and pattern of tooth agenesis, microdontia, and palatally displaced canine (PDC) in women diagnosed with papillary thyroid cancer (PTC), compared to a control group of women without any malignancy or thyroid disease.

MATERIALS AND METHODS

This case-control study was carried at the Department of Orthodontics, School of Dental Medicine University of Zagreb, and Department of Oncology and Nuclear Medicine Sestre Milosrdnice University Hospital Centre. The study involved a clinical examination and evaluation of dental status, panoramic X-ray analysis, and assessment of medical and family history of 116 female patients aged 20-40 with PTC, as well as 424 females in the control group who were of similar age.

RESULTS

The prevalence of hypodontia, microdontia, and PDC was statistically higher in women with PTC than in the control group. The prevalence rate of hypodontia was 11.3% in the experimental group and 3.5% in the control group. The experimental group showed a higher occurrence of missing upper lateral incisors, lower left central incisors, and all the third molars (except the upper left) compared to the control group. Women with PTC showed the prevalence of PDC significantly higher than the control group (3.5%, 0.7%, p = 0.002). The probability of hypodontia as a clinical finding increases 2.6 times, and microdontia occurs 7.7 times more frequently in women with PTC.

CONCLUSION

Our study suggests a possible link between odontogenesis and PTC. The absence of permanent teeth may increase the likelihood of PTC in women. Leveraging the age-7 orthopantomogram to identify women at high risk for PTC within a critical early detection window could significantly improve oral health outcomes and PTC prognosis through proactive interventions.

Tooth agenesis patterns and variants in PAX9: A systematic review

Mutations in PAX9 are the most common genetic cause of tooth agenesis (TA). The aim of this study was to systematically review the profiles of the TA and PAX9 variants and establish their genotype-phenotype correlation. Forty articles were eligible for 178 patients and 61 mutations (26 in frame and 32 null mutations). PAX9 mutations predominantly affected molars, mostly the second molar, and the mandibular first premolar was the least affected. More missing teeth were found in the maxilla than the mandible, and with null mutations than in-frame mutations. The number of missing teeth was correlated with the locations of the in-frame mutations with the C-terminus mutations demonstrating the fewest missing teeth. The null mutation location did not influence the number of missing teeth. Null mutations in all locations predominantly affected molars. For the in-frame mutations, a missing second molar was commonly associated with mutations in the highly conserved paired DNA-binding domain, particularly the linking peptide (100% prevalence). In contrast, C-terminus mutations were rarely associated with missing second molars and anterior teeth, but were commonly related to an absent second premolar. These finding indicate that the mutation type and position contribute to different degrees of loss of PAX9 function that further differentially influences the manifestations of TA. This study provides novel information on the correlation of the PAX9 genotype-phenotype, aiding in the genetic counseling for TA.

Phenotypic characteristics of taurodontism and a novel WNT10A variant in non-syndromic oligodontia family

OBJECTIVE

Variants in wingless-type MMTV integration site family member 10A (WNT10A) have been proposed to be the most common cause of non-syndromic oligodontia (NSO). The goal of the present study was to identify the novel WNT10A variants in Chinese families with NSO.

DESIGN

Clinical data were collected from 39 families with oligodontia admitted to the Hospital of Stomatology Hebei Medical University (China) from 2016 to 2022. Whole-exome sequencing (WES) and Sanger sequencing were performed to identify WNT10A variants in three families with non-syndromic oligodontia. Amino acid conservation analysis and protein conformational analysis were conducted for the WNT10A variant. Genotype-phenotype analysis was performed on the previously reported WNT10A variants related to NSO.

RESULTS

We found a novel heterozygous WNT10A variant c.1127 G>A (p.Cys376Tyr) and two reported heterozygous variants c.460 C>A (p.Leu154Met) and c.511 C>T (p.Arg171Cys). Structural modeling showed that the novel WNT10A variant was located in a highly conserved domain, which led to structural damage of WNT10A protein. In addition, we found that the phenotype of the WNT10A variants affected the maxillary second premolars, followed by the mandibular second premolars, and rarely affected the maxillary central incisor. Herein, it is the first time to report that NSO patients with WNT10A monoallele mutation carry taurodontism phenotype and 6.1% prevalence of taurodontism in WNT10A-related NSO patients.

CONCLUSIONS

Our results demonstrated that the novel variant c.1127 G>A (p.Cys376Tyr) of WNT10A causes NSO. The present study expanded the known variation spectrum of WNT10A and provided valuable information for genetic counseling of families.

PAX9 mutations and genetic synergism in familial tooth agenesis

Familial tooth agenesis (FTA) is one of the most common craniofacial anomalies in humans. Loss-of-function mutations in PAX9 and WNT10A have been known to cause FTA with various expressivity. In this study, we identified five FTA kindreds with novel PAX9 disease-causing mutations: p.(Glu7Lys), p.(Val83Leu), p.(Pro118Ser), p.(Ser197Argfs*23), and c.771+4A>G. Concomitant PAX9 and WNT10A pathogenic variants found in two probands with severe phenotypes suggested an effect of mutational synergism. All overexpressed PAX9s showed proper nuclear localization, excepting the p.(Pro118Ser) mutant. Various missense mutations caused differential loss of PAX9 transcriptional ability. PAX9 overexpression in dental pulp cells upregulated LEF1 and AXIN2 expression, indicating a positive regulatory role for PAX9 in canonical Wnt signaling. Analyzing 176 cases with 63 different mutations, we observed a distinct pattern of tooth agenesis for PAX9-associated FTA: Maxillary teeth are in general more frequently affected than mandibular ones. Along with all second molars, maxillary bicuspids and first molars are mostly involved, while maxillary lateral incisors and mandibular bicuspids are relatively less affected. Genotypically, missense mutations are associated with fewer missing teeth than frameshift and nonsense variants. This study significantly expands the phenotypic and genotypic spectrums of PAX9-associated disorders and reveals a molecular mechanism of genetic synergism underlying FTA variable expressivity.

Genotype-phenotype pattern analysis of pathogenic PAX9 variants in Chinese Han families with non-syndromic oligodontia

Background: Non-syndromic oligodontia is characterized by the absence of six or more permanent teeth, excluding third molars, and can have aesthetic, masticatory, and psychological consequences. Previous studies have shown that PAX9 is associated with autosomal dominant forms of oligodontia but the precise molecular mechanisms are still unknown.

Methods: Whole-exome and Sanger sequencing were performed on a cohort of approximately 28 probands with NSO, for mutation analysis. Bioinformatic analysis was performed on the potential variants. Immunofluorescence assay, western blotting, and qPCR were used to explore the preliminary functional impact of the variant PAX9 proteins. We reviewed PAX9-related NSO articles in PubMed to analyze the genotype-phenotype correlations.

Results: We identified three novel PAX9 variants in Chinese Han families: c.152G&gt;T (p.Gly51Val), c.239delC (p.Thr82Profs*3), and c.409C&gt;T (q.Gln137Ter). In addition, two previously reported missense variants were identified: c.140G&gt;C (p.Arg47Pro) and c.146C&gt;T (p.Ser49Leu) (reference sequence NM_006194.4). Structural modeling revealed that all missense variants were located in the highly conserved paired domain. The other variants led to premature termination of the protein, causing structural impairment of the PAX9 protein. Immunofluorescence assay showed abnormal subcellular localizations of the missense variants (R47P, S49L, and G51V). In human dental pulp stem cells, western blotting and qPCR showed decreased expression of PAX9 variants (c.140G&gt;C, p.R47P, and c.152G&gt;T, p.G51V) compared with the wild-type group at both the transcription and translation levels. A review of published papers identified 64 PAX9 variants related to NSO and found that the most dominant feature was the high incidence of missing upper second molars, first molars, second premolars, and lower second molars.

Conclusion: Three novel PAX9 variants were identified in Chinese Han families with NSO. These results extend the variant spectrum of PAX9 and provide a foundation for genetic diagnosis and counseling.

Genetic/Protein Association of Atopic Dermatitis and Tooth Agenesis

Atopic dermatitis and abnormalities in tooth development (including hypomineralization, hypodontia and microdontia) have been observed to co-occur in some patients. A common pathogenesis pathway that involves genes and protein interactions has been hypothesized. This review aims to first provide a description of the key gene mutations and signaling pathways associated with atopic dermatitis and tooth agenesis (i.e., the absence of teeth due to developmental failure) and identify the possible association between the two diseases. Second, utilizing a list of genes most commonly associated with the two diseases, we conducted a protein–protein network interaction analysis using the STRING database and identified a novel association between the Wnt/β-catenin signaling pathway (major pathway responsible for TA) and desmosomal proteins (component of skin barrier that affect the pathogenesis of AD). Further investigation into the mechanisms that may drive their co-occurrence and underlie the development of the two diseases is warranted.

Tooth number abnormality: from bench to bedside

Tooth number abnormality is one of the most common dental developmental diseases, which includes both tooth agenesis and supernumerary teeth. Tooth development is regulated by numerous developmental signals, such as the well-known Wnt, BMP, FGF, Shh and Eda pathways, which mediate the ongoing complex interactions between epithelium and mesenchyme. Abnormal expression of these crutial signalling during this process may eventually lead to the development of anomalies in tooth number; however, the underlying mechanisms remain elusive. In this review, we summarized the major process of tooth development, the latest progress of mechanism studies and newly reported clinical investigations of tooth number abnormality. In addition, potential treatment approaches for tooth number abnormality based on developmental biology are also discussed. This review not only provides a reference for the diagnosis and treatment of tooth number abnormality in clinical practice but also facilitates the translation of basic research to the clinical application.

Novel PAX9 compound heterozygous variants in a Chinese family with non-syndromic oligodontia and genotype-phenotype analysis of PAX9 variants

OBJECTIVE

Studies have reported that >91.9% of non-syndromic tooth agenesis cases are caused by seven pathogenic genes. To report novel heterozygous PAX9 variants in a Chinese family with non-syndromic oligodontia and summarize the reported genotype-phenotype relationship of PAX9 variants.

METHODOLOGY

We recruited 28 patients with non-syndromic oligodontia who were admitted to the Hospital of Stomatology Hebei Medical University (China) from 2018 to 2021. Peripheral blood was collected from the probands and their core family members for whole-exome sequencing (WES) and variants were verified by Sanger sequencing. Bioinformatics tools were used to predict the pathogenicity of the variants. SWISS-MODEL homology modeling was used to analyze the three-dimensional structural changes of variant proteins. We also analyzed the genotype-phenotype relationships of PAX9 variants.

RESULTS

We identified novel compound heterozygous PAX9 variants (reference sequence NM_001372076.1) in a Chinese family with non-syndromic oligodontia: a new missense variant c.1010C>A (p.T337K) in exon 4 and a new frameshift variant c.330_331insGT (p.D113Afs*9) in exon 2, which was identified as the pathogenic variant in this family. This discovery expands the known variant spectrum of PAX9; then, we summarized the phenotypes of non-syndromic oligodontia with PAX9 variants.

CONCLUSION

We found that PAX9 variants commonly lead to loss of the second molars.

A Novel CDH1 Variant Identified in a Chinese Family with Blepharocheilodontic Syndrome

The goal of the current study was to identify the pathogenic gene variant in a Chinese family with Blepharocheilodontic (BCD) syndrome. Whole-exome sequencing (WES) and Sanger sequencing were used to identify the pathogenic gene variant. The harmfulness of the variant was predicted by bioinformatics. We identified a novel heterozygous missense variant c.1198G>A (p.Asp400Asn) in the CDH1 gene in the proband and his mother with BCD syndrome. The sequencing results of three healthy individuals in this family are wild type. This result is consistent with familial co-segregation. According to ReVe, REVEL, CADD, gnomAD, dbSNP, and the classification of pathogenic variants with the standards of the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG), c.1198G>A (p.Asp400Asn) is predicted to be a likely pathogenic. We observed that variant c.1198G>A (p.Asp400Asn) was located in the extracellular cadherin-type repeats in CDH1. Amino acid sequence alignment of the CDH1 protein among multiple species showed that Asp400 was highly evolutionarily conserved. The conformational analysis showed that this variant might cause structural damage to the CDH1 protein. Phenotypic analysis revealed unique dental phenotypes in patients with BCD syndrome, such as oligodontia, conical-shaped teeth, and notching of the incisal edges. Our results broaden the variation spectrum of BCD syndrome and phenotype spectrum of CDH1, which can help with the clinical diagnosis, treatment, and genetic counseling in relation to BCD syndrome.

KDF1 Novel Variant Causes Unique Dental and Oral Epithelial Defects

Keratinocyte differentiation factor 1 (KDF1) is a recently identified and rare candidate gene for human tooth agenesis; however, KDF1-related morphological characteristics and pathological changes in dental tissue and the oral epithelium remain largely unknown. Here, we employed whole-exome sequencing (WES) and Sanger sequencing to screen for the suspected variants in a cohort of 151 tooth agenesis patients, and we segregated a novel KDF1 heterozygous missense variation, c.920G>C (p.R307P), in a non-syndromic tooth agenesis family. Essential bioinformatics analyses and tertiary structural predictions were performed to analyze the structural changes and functional impacts of the novel KDF1 variant. The subsequent functional assessment using a TOP-flash/FOP-flash luciferase reporter system demonstrated that KDF1 variants suppressed the activation of canonical Wnt signaling in 293T cells. To comprehensively investigate the KDF1-related oral morphological anomalies, we performed scanning electron microscopy and ground section of the lower right lateral deciduous incisor extracted from #285 proband, and histopathological assessment of the gingiva. The phenotypic analyses revealed a series of tooth morphological anomalies related to the KDF1 variant R307P, including a shovel-shaped lingual surface of incisors and cornicione-shaped marginal ridges with anomalous morphological occlusal grooves of premolars and molars. Notably, keratinized gingival epithelium abnormalities were revealed in the proband and characterized by epithelial dyskeratosis with residual nuclei, indistinct stratum granulosum, epithelial hyperproliferation, and impaired epithelial differentiation. Our findings revealed new developmental anomalies in the tooth and gingival epithelium of a non-syndromic tooth agenesis individual with a novel pathogenic KDF1 variant, broadening the phenotypic spectrum of KDF1-related disorders and providing new evidence for the crucial role of KDF1 in regulating human dental and oral epithelial development.

Mutation analysis in patients with nonsyndromic tooth agenesis using exome sequencing

BACKGROUND

Tooth agenesis (TA) is a congenital abnormality that may present as syndromic or nonsyndromic. Considering its complex genetic aetiology, the aim of this study was to uncover the pathogenic mutants in patients with nonsyndromic TA and analyse the characteristics of these mutants.

METHODS

Exome sequencing was performed to detect pathogenic variants in 72 patients from 43 unrelated families with nonsyndromic TA. All candidate variants were validated using Sanger sequencing. Bioinformatics and conformational analyses were performed to determine the pathogenic mechanisms of the mutants.

RESULTS

The following eight mutations (six novel and two known) in six genes were identified in eight families: WNT10A [c.742C > T (p.R248*)], LRP6 [c.1518G > A (p.W506*), c.2791 + 1G > T], AXIN2 [c.133_134insGCCAGG (p.44_45insGQ)], PAX9 [c.439C > T (p.Q147*), c.453_454insCCAGC (p.L154QfsTer60)], MSX1 [c.603_604del (p.A203GfsTer10)] and PITX2 [c.522C > G (p.Y174*)]. Bioinformatics and conformational analyses showed that the protein structures were severely altered in these mutants, and indicated that these structural abnormalities may cause functional disabilities.

CONCLUSIONS

Our study extends the mutation spectrum in patients with nonsyndromic TA and provides valuable data for genetic counselling. The pathogenic mechanisms of TA in patients/families with unknown causative variants need to be explored further.

Non-syndromic familial congenital dental deficiency: two cases report

Congenital dental deficiency can lead to aesthetic and masticatory dysfunction, which have a great effect on the quality of life of patients. Genetic inheritance is the determining factor of congenital dental deficiency, which may follow the pattern of autosomal dominant, recessive, or sex chromosome inheritance. However, the specific genetic mechanisms are not clear. The prevalence of congenital absence of permanent teeth in the general population worldwide are not high, and familial oligodontia in clinically healthy patients is rare. This paper reported two cases of familial non-syndromic congenital teeth loss and included a review of literature referring to the etiology, clinical manifestations, and treatment of congenital dental deficiency.

Four Novel PAX9 Variants and the PAX9-Related Non-Syndromic Tooth Agenesis Patterns

The purpose of this research was to investigate and identify PAX9 gene variants in four Chinese families with non-syndromic tooth agenesis. We identified pathogenic gene variants by whole-exome sequencing (WES) and Sanger sequencing and then studied the effects of these variants on function by bioinformatics analysis and in vitro experiments. Four novel PAX9 heterozygous variants were identified: two missense variants (c.191G > T (p.G64V) and c.350T > G (p.V117G)) and two frameshift variants (c.352delC (p.S119Pfs*2) and c.648_649insC(p.Y217Lfs*100)). The bioinformatics analysis showed that these variants might be pathogenic. The tertiary structure analysis showed that these four variants could cause structural damage to PAX9 proteins. In vitro functional studies demonstrated that (1) the p.Y217Lfs*100 variant greatly affects mRNA stability, thereby affecting endogenous expression; (2) the p. S119Pfs* 2 variant impairs the subcellular localization of the nuclear expression of the wild-type PAX9 protein; and (3) the four variants (p.G64V, p.V117G, p.S119Pfs*2, and p.Y217Lfs*100) all significantly affect the downstream transcriptional activity of the BMP4 gene. In addition, we summarized and analyzed tooth missing positions caused by PAX9 variants and found that the maxillary second molar (84.11%) and mandibular second molar (84.11%) were the most affected tooth positions by summarizing and analyzing the PAX9-related non-syndromic tooth agenesis positions. Our results broaden the variant spectrum of the PAX9 gene related to non-syndromic tooth agenesis and provide useful information for future genetic counseling.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Detection of Novel Variant and Functional Study in a Chinese Family with Non-syndromic Oligodontia

OBJECTIVES

To investigate the pathogenic gene of a patient with non-syndromic oligodontia, and analyze its possible pathogenic mechanism.

SUBJECTS AND METHODS

The variant was detected by whole exome sequencing (WES) and Sanger sequencing in a family with oligodontia. Bioinformatic and structural analyses were used to analyze variant. Functional studies including western blotting and immunofluorescent analyses and luciferase reporter assay were conducted to explore the functional effects.

RESULTS

We identified a novel frameshift variant of PAX9 (c.491-510delGCCCT-ATCACGGCGGCGGCC, p.P165Qfs*145) outside the DNA-binding domain causing an autosomal-dominant non-syndromic oligodontia in a Chinese family. Bioinformatic and structural analyses revealed that the variant is pathogenic and conserved evolutionarily, and the changes might affect protein stability or folding. Functional studies demonstrate dramatically reduced ability in activating transcription activity of BMP4 promoter and a marked decrease in protein production, as evaluated by western blotting and immunofluorescent analyses.

CONCLUSIONS

We found a novel frameshift variant of PAX9 causing non-syndromic oligodontia in a Chinese family. Our findings indicate that frameshift variants cause loss of function of PAX9 protein during the patterning of the dentition and the subsequent tooth agenesis, providing new molecular insights into the role of frameshift variant of PAX9 and broaden the pathogenic spectrum of PAX9 variants.

Identification of potentially functional circRNAs and prediction of circRNA-miRNA-mRNA regulatory network in periodontitis: Bridging the gap between bioinformatics and clinical needs

Background and Objective

Periodontitis is a multifactorial chronic inflammatory disease that can lead to the irreversible destruction of dental support tissues. As an epigenetic factor, the expression of circRNA is tissue‐dependent and disease‐dependent. This study aimed to identify novel periodontitis‐associated circRNAs and predict relevant circRNA‐periodontitis regulatory network by using recently developed bioinformatic tools and integrating sequencing profiling with clinical information for getting a better and more thorough image of periodontitis pathogenesis, from gene to clinic.

Material and Methods

High‐throughput sequencing and RT‐qPCR were conducted to identify differentially expressed circRNAs in gingival tissues from periodontitis patients. The relationship between upregulated circRNAs expression and probing depth (PD) was performed using Spearman's correlation analysis. Bioinformatic analyses including GO analysis, circRNA‐disease association prediction, and circRNA‐miRNA‐mRNA network prediction were performed to clarify potential regulatory functions of identified circRNAs in periodontitis. A receiver‐operating characteristic (ROC) curve was established to assess the diagnostic significance of identified circRNAs.

Results

High‐throughput sequencing identified 70 differentially expressed circRNAs (68 upregulated and 2 downregulated circRNAs) in human periodontitis (fold change >2.0 and p < .05). The top five upregulated circRNAs were validated by RT‐qPCR that had strong associations with multiple human diseases, including periodontitis. The upregulation of circRNAs were positively correlated with PD (R = .40–.69, p < .05, moderate). A circRNA‐miRNA‐mRNA network with the top five upregulated circRNAs, differentially expressed mRNAs, and overlapped predicted miRNAs indicated potential roles of circRNAs in immune response, cell apoptosis, migration, adhesion, and reaction to oxidative stress. The ROC curve showed that circRNAs had potential value in periodontitis diagnosis (AUC = 0.7321–0.8667, p < .05).

Conclusion

CircRNA‐disease associations were predicted by online bioinformatic tools. Positive correlation between upregulated circRNAs, circPTP4A2, chr22:23101560‐23135351+, circARHGEF28, circBARD1 and circRASA2, and PD suggested function of circRNAs in periodontitis. Network prediction further focused on downstream targets regulated by circRNAs during periodontitis pathogenesis.

Patterns of molar agenesis associated with p.P20L and p.R77Q variants in PAX9

Nonsyndromic tooth agenesis is associated with variants in several genes. There are numerous genotype-phenotype publications involving many patients and kindreds. Here, we identified six Thai individuals in two families with nonsyndromic tooth agenesis, performed exome sequencing, and conducted functional experiments. Family 1 had four affected members carrying the heterozygous PAX9 variant, c.59C>T (p.Pro20Leu). The p.Pro20Leu was previously reported in two families having four and three affected members. These seven cases and Proband-1 had agenesis of at least three third molars. Family 2 comprised two affected members with agenesis of all 12 molars. Both individuals were heterozygous for c.230G>A (p.Arg77Gln) in PAX9, which has not been reported previously. This variant is predicted to be damaging, evolutionarily conserved, and resides in the PAX9 linking peptide. The BMP4 RNA levels in Proband-1's leukocytes were not significantly different from those in the controls, whereas BMP4 levels observed in Proband-2 were significantly increased. Moreover, the p.Arg77Gln variant demonstrated nuclear localization similar to the wild-type but resulted in significantly impaired transactivation of BMP4, a PAX9 downstream gene. In conclusion, we demonstrate that the PAX9 p.Pro20Leu is highly associated with absent third molars, while the novel PAX9 p.Arg77Gln impairs BMP4 transactivation and is associated with total molar agenesis.

Crucial Roles of microRNA-16-5p and microRNA-27b-3p in Ameloblast Differentiation Through Regulation of Genes Associated With Amelogenesis Imperfecta

Amelogenesis imperfecta is a congenital disorder within a heterogeneous group of conditions characterized by enamel hypoplasia. Patients suffer from early tooth loss, social embarrassment, eating difficulties, and pain due to an abnormally thin, soft, fragile, and discolored enamel with poor aesthetics and functionality. The etiology of amelogenesis imperfecta is complicated by genetic interactions. To identify mouse amelogenesis imperfecta-related genes (mAIGenes) and their respective phenotypes, we conducted a systematic literature review and database search and found and curated 70 mAIGenes across all of the databases. Our pathway enrichment analysis indicated that these genes were enriched in tooth development-associated pathways, forming four distinct groups. To explore how these genes are regulated and affect the phenotype, we predicted microRNA (miRNA)-gene interaction pairs using our bioinformatics pipeline. Our miRNA regulatory network analysis pinpointed that miR-16-5p, miR-27b-3p, and miR-23a/b-3p were hub miRNAs. The function of these hub miRNAs was evaluated through ameloblast differentiation assays with/without the candidate miRNA mimics using cultured mouse ameloblast cells. Our results revealed that overexpression of miR-16-5p and miR-27b-3p, but not miR-23a/b-3p, significantly inhibited ameloblast differentiation through regulation of mAIGenes. Thus, our study shows that miR-16-5p and miR-27b-3p are candidate pathogenic miRNAs for amelogenesis imperfecta.

Analyses of oligodontia phenotypes and genetic etiologies

Oligodontia is the congenital absence of six or more teeth and comprises the more severe forms of tooth agenesis. Many genes have been implicated in the etiology of tooth agenesis, which is highly variable in its clinical presentation. The purpose of this study was to identify associations between genetic mutations and clinical features of oligodontia patients. An online systematic search of papers published from January 1992 to June 2021 identified 381 oligodontia cases meeting the eligibility criteria of causative gene mutation, phenotype description, and radiographic records. Additionally, ten families with oligodontia were recruited and their genetic etiologies were determined by whole-exome sequence analyses. We identified a novel mutation in WNT10A (c.99_105dup) and eight previously reported mutations in WNT10A (c.433 G > A; c.682 T > A; c.318 C > G; c.511.C > T; c.321 C > A), EDAR (c.581 C > T), and LRP6 (c.1003 C > T, c.2747 G > T). Collectively, 20 different causative genes were implicated among those 393 cases with oligodontia. For each causative gene, the mean number of missing teeth per case and the frequency of teeth missing at each position were calculated. Genotype-phenotype correlation analysis indicated that molars agenesis is more likely linked to PAX9 mutations, mandibular first premolar agenesis is least associated with PAX9 mutations. Mandibular incisors and maxillary lateral incisor agenesis are most closely linked to EDA mutations.

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 novel EDAR missense mutation identified by whole-exome sequencing with non-syndromic tooth agenesis in a Chinese family

Background

Causative variants in genes of the EDA/EDAR/NF‐κB pathway, such as EDA and EDARADD, have been widely identified in patients with non‐syndromic tooth agenesis (NSTA). However, few cases of NSTA are due to ectodysplasin‐A receptor (EDAR) variants. In this study, we investigated NSTA‐associated variants in Chinese families.

Methods

Peripheral blood samples were collected from the family members of 24 individuals with NSTA for DNA extraction. The coding region of the EDA gene of the 24 probands was amplified by PCR and sequenced to investigate new variants. Whole‐exome sequencing and Sanger sequencing were then performed for probands without EDA variants detected by PCR.

Results

A novel missense variant EDAR c.338G>A (p.(Cys113Tyr)) was identified in one family. In addition, three known EDA variants (c.865C>T, c.866G>A, and c.1013C>T) were identified in three families. Genotype–phenotype correlation analysis of EDAR gene mutation showed that NSTA patients were most likely to lose the maxillary lateral incisors and the maxillary central incisors were the least affected. The phenotype of mutations at codon 289 of EDA in NSTA affected patients was characterized by lateral incisors loss, rarely affecting the maxillary first molars.

Conclusion

A novel EDAR missense variant c.338G>A (p.(Cys113Tyr)) was identified in a family with NSTA, extending the mutation spectrum of the EDAR gene. Genotype–phenotype correlation analyses of EDAR and EDA mutations could help to improve disease status prediction in NSTA families.

Tooth agenesis: What do we know and is there a connection to cancer?

Like all developmental processes, odontogenesis is highly complex and dynamically regulated, with hundreds of genes co-expressed in reciprocal networks. Tooth agenesis (missing one or more/all teeth) is a common human craniofacial anomaly and may be caused by genetic variations and/or environmental factors. Variants in PAX9, MSX1, AXIN2, EDA, EDAR, and WNT10A genes are associated with tooth agenesis. Currently, variants in ATF1, DUSP10, CASC8, IRF6, KDF1, GREM2, LTBP3, and components and regulators of WNT signaling WNT10B, LRP6, DKK, and KREMEN1 are at the forefront of interest. Due to the interconnectedness of the signaling pathways of carcinogenesis and odontogenesis, tooth agenesis could be a suitable marker for early detection of cancer predisposition. Variants in genes associated with tooth agenesis could serve as prognostic or therapeutic targets in cancer. This review aims to summarize existing knowledge of development and clinical genetics of teeth. Concurrently, the review proposes possible approaches for future research in this area, with particular attention to roles in monitoring, early diagnosis and therapy of tumors associated with defective tooth development.

Activation of EGFR-Aurora A induces loss of primary cilia in oral squamous cell carcinoma

OBJECTIVE

Primary cilia, evolutionally conserved organelles involving multiple cell functions, are frequently lost in various cancers. However, little is known about the role of primary cilia in oral squamous cell carcinoma (OSCC).

METHODS

Immunofluorescence staining was applied to detect primary cilia in normal, oral leukoplakia (OLK) and OSCC tissues. Differentially expressed ciliary genes of OSCC were screened from the TCGA database. Immunohistochemical analysis was used for validating the correlation between the expression of interested proteins and primary cilia, and their regulatory effect on primary cilia was further proved in vitro and in vivo.

RESULTS

A significant decrease in cilia ratio was found in OLK, especially in OSCC. Multiple ciliary genes were abnormally expressed in OSCC and epidermal growth factor receptor (EGFR)-Aurora A signaling was chosen for further study. A parallel increase of EGFR-Aurora A was observed in OLK and OSCC tissues. Moreover, EGFR activation induced obvious cilia absorption by phosphorylating Aurora A. Besides, Aurora A silencing significantly restored ciliary expression and decreased tumor growth in vivo.

CONCLUSIONS

The abnormal activation of EGFR-Aurora A leads to the gradual loss of primary cilia in oral mucosa carcinogenesis. Primary cilia have the potential to be new biomarkers and therapeutic targets of oral cancer.

Transcriptome Analysis Reveals High Similarities between Adult Human Cardiac Stem Cells and Neural Crest-Derived Stem Cells

For the identification of a stem cell population, the comparison of transcriptome data enables the simultaneous analysis of tens of thousands of molecular markers and thus enables the precise distinction of even closely related populations. Here, we utilized global gene expression profiling to compare two adult human stem cell populations, namely neural crest-derived inferior turbinate stem cells (ITSCs) of the nasal cavity and human cardiac stem cells (hCSCs) from the heart auricle. We detected high similarities between the transcriptomes of both stem cell populations, particularly including a range of neural crest-associated genes. However, global gene expression likewise reflected differences between the stem cell populations with regard to their niches of origin. In a broader analysis, we further identified clear similarities between ITSCs, hCSCs and other adherent stem cell populations compared to non-adherent hematopoietic progenitor cells. In summary, our observations reveal high similarities between adult human cardiac stem cells and neural crest-derived stem cells from the nasal cavity, which include a shared relation to the neural crest. The analyses provided here may help to understand underlying molecular regulators determining differences between adult human stem cell populations.

Lrp6 Dynamic Expression in Tooth Development and Mutations in Oligodontia

Genes associated with the WNT pathway play an important role in the etiology of tooth agenesis. Low-density lipoprotein receptor-related protein 6 encoding gene (LRP6) is a recently defined gene that is associated with autosomal dominant inherited tooth agenesis. Here, we aimed to identify novel LRP6 mutations in patients with tooth agenesis and investigate the significance of Lrp6 during tooth development. Using whole-exome sequencing, we identified 4 novel LRP6 heterozygous mutations (c.2292G>A, c.195dup, c.1095dup, and c.1681C>T) in 4 of 77 oligodontia patients. Notably, a patient who carried a nonsense LRP6 mutation (c.2292G>A; p.W764*) presented a hypohidrotic ectodermal dysplasia phenotype. Preliminary functional studies, including bioinformatics analysis and TOP-/FOP-flash reporter assays, demonstrated that the activation of WNT/β-catenin signaling was compromised as a consequence of LRP6 mutations. RNAscope in situ hybridization revealed dynamic and special changes of Lrp6 expression during murine tooth development from E11.5 to E16.5. It was noteworthy that Lrp6 was specifically expressed in the epithelium at E11.5 to E13.5 but was expressed in both dental epithelium and dental papilla from E14.5 and persisted in both tissues at later stages. Our study broadens the mutation spectrum of human tooth agenesis and is the first to identify a LRP6 mutation in patients with hypohidrotic ectodermal dysplasia and reveal the dynamic expression pattern of Lrp6 during tooth development. Information from this study is conducive to understanding the functional significance of Lrp6 on the biological process of tooth development.

Functional study of novel PAX9 variants: The paired domain and non-syndromic oligodontia

OBJECTIVES

To investigate pathogenic variants of the paired box 9 (PAX9) gene in patients with non-syndromic oligodontia, and the functional impact of these variants.

SUBJECTS AND METHODS

Whole exome sequencing and Sanger sequencing were utilized to detect gene variants in a cohort of 80 patients diagnosed with non-syndromic oligodontia. Bioinformatic and conformational analyses, fluorescence microscopy and luciferase reporter assay were employed to explore the functional impact.

RESULTS

We identified three novel variants in the PAX9, including two frameshift variants (c.211_212insA; p.I71Nfs*246 and c.236_237insAC; p.T80Lfs*6), and one missense variant (c.229C > G; p.R77G). Familial co-segregation verified an autosomal-dominant inheritance pattern. Conformational analyses revealed that the variants resided in the paired domain, and could cause corresponding structural impairment of the PAX9 protein. Fluorescence microscopy showed abnormal subcellular localizations of frameshift variants, and luciferase assay showed impaired downstream transactivation activities of the bone morphogenetic protein 4 (BMP4) gene in all variants.

CONCLUSIONS

Our findings broaden the spectrum of PAX9 variants in patients with non-syndromic oligodontia and support that paired domain structural impairment and the dominant-negative effect are likely the underlying mechanisms of PAX9-related non-syndromic oligodontia. Our findings will facilitate genetic diagnosis and counselling, and help lay the foundation for precise oral health therapies.

Genetic Variants in miRNAs Are Associated With Risk of Non-syndromic Tooth Agenesis

Non-syndromic tooth agenesis (NSTA) is one of the most common dental abnormalities. MiRNAs participated in the craniofacial and tooth development. Therefore, single nucleotide polymorphisms (SNPs) in miRNA genes may contribute to the susceptibility of non-syndromic tooth agenesis. Here, a total of 625 non-syndromic tooth agenesis cases and 1,144 healthy controls were recruited, and four miRNA SNPs (miR-146a/rs2910164, miR-196a2/rs11614913, pre-miR-605/rs2043556, pre-miR-618/rs2682818) were genotyped by the TaqMan platform. Rs2043556 showed nominal associations with risk of non-syndromic tooth agenesis (P _Add = 0.021) in the overall analysis, as well as upper lateral incisor agenesis (P _Add = 0.047) and lower incisor agenesis (P _Add = 0.049) in the subgroup analysis. Notably, its significant association with upper canine agenesis was observed (P _Add = 0.0016). Rs2043556 affected the mature of miR-605-3p and miR-605-5p while dual-luciferase report analysis indicated that MDM2 was the binding target of miR-605-5p. Our study indicated that pre-miR-605 rs2043556 was associated with risk of non-syndromic tooth agenesis.

Paired Box 9 (PAX9), the RNA polymerase II transcription factor, regulates human ribosome biogenesis and craniofacial development

Dysregulation of ribosome production can lead to a number of developmental disorders called ribosomopathies. Despite the ubiquitous requirement for these cellular machines used in protein synthesis, ribosomopathies manifest in a tissue-specific manner, with many affecting the development of the face. Here we reveal yet another connection between craniofacial development and making ribosomes through the protein Paired Box 9 (PAX9). PAX9 functions as an RNA Polymerase II transcription factor to regulate the expression of proteins required for craniofacial and tooth development in humans. We now expand this function of PAX9 by demonstrating that PAX9 acts outside of the cell nucleolus to regulate the levels of proteins critical for building the small subunit of the ribosome. This function of PAX9 is conserved to the organism Xenopus tropicalis, an established model for human ribosomopathies. Depletion of pax9 leads to craniofacial defects due to abnormalities in neural crest development, a result consistent with that found for depletion of other ribosome biogenesis factors. This work highlights an unexpected layer of how the making of ribosomes is regulated in human cells and during embryonic development.

Screening PAX9, MSX1 and WNT10A Mutations in 4 Iranian Families with Non-Syndromic Tooth Agenesis

BACKGROUND

Tooth agenesis is one of the most common developmental anomalies in human and the main reasons for its occurrence are still unknown. Mutations of several genes such as PAX9, MSX1, AXIN2, KDF1 and WNT10A have been reported which are associated with non-syndromic tooth agenesis. However, PAX9, MSX1 and WNT10A are commonly reported in the literature. Hence, the aim of this study was to investigate the mutations of these genes in 4 Iranian families with non-syndromic tooth agenesis.

METHODS

DNA extractions from peripheral blood cells of patients with non-syndromic tooth agenesis from 4 unrelated Iranian families were performed by salting out method, and the candidate genes were amplified then followed by Sanger sequencing method.

RESULTS

One missense variant (rs4904210) and 4 Single Nucleotide Polymorphisms (SNPs) (rs2236007, rs12883298, rs12882923 and rs12883049) were found in PAX9 gene. Five variants (rs149370601, rs8670, rs186861426 and rs774949973) including a missense variant (rs36059701) were detected in MSX1 gene and no variants were found in WNT10A gene.

CONCLUSION

All variants were analyzed based on bioinformatics websites and Iranian gene databases, and as a result, it was revealed that variants of PAX9, MSX1 and WNT10A may not play a role in non-syndromic tooth agenesis among Iranian cases.

Novel PITX2 mutations identified in Axenfeld-Rieger syndrome and the pattern of PITX2-related tooth agenesis

OBJECTIVES

To investigate the mutations in patients with Axenfeld-Rieger syndrome (ARS) and the pattern of PITX2-related tooth agenesis.

METHODS

Whole-exome sequencing (WES) and copy number variation (CNV) array were used to screen the mutations in four ARS probands. After Sanger sequencing and quantitative polymerase chain reaction (qPCR) validation, secondary structure prediction and dual-luciferase assay were employed to investigate the functional impact. Eighteen PITX2-mutated patients with definite dental records were retrieved from our database and literatures, and the pattern of PITX2-related tooth agenesis was analyzed.

RESULTS

A novel de novo segmental deletion of chromosome 4q25 (GRCh37/hg19 chr4:111, 320, 052-111, 754, 236) encompassing PITX2 and three novel PITX2 mutations c.148C > T, c.257G > A, and c.630insCG were identified. Preliminary functional studies indicated the transactivation capacity of mutant PITX2 on Distal-less homeobox 2 (DLX2) promoter was compromised. The maxillary teeth showed significantly higher rate of agenesis (57.94%) than the mandibular teeth (44.05%). The most often missing teeth were upper lateral incisors (83.33%) and upper second premolars (69.44%). Teeth with the least agenesis rate were the lower second molars (19.44%) and lower first molars (8.33%).

CONCLUSIONS

We identified a novel 4q25 microdeletion including PITX2 and three novel PITX2 mutations, and statistically analyzed the PITX2-related tooth agenesis pattern.

BMP4 mutations in tooth agenesis and low bone mass

OBJECTIVE

To identify an uncommon genetic cause of tooth agenesis (TA) by utilizing whole exome sequencing (WES) and targeted Sanger sequencing in a cohort of 120 patients with isolated TA.

DESIGN

One deleterious mutation in the gene encoding bone morphogenetic protein 4 (BMP4) was identified in 6 unrelated patients with TA by WES. After that, the coding exons of BMP4 were examined in 114 TA patients using Sanger sequencing. Dual-energy X-ray absorptiometry (DEXA) was used to measure the bone mineral density of patients who carried a BMP4 mutation. Finally, preliminary functional studies of two BMP4 mutants were performed.

RESULTS

We detected 3 novel missense mutations (c.58 G > A: p.Gly20Ser, c.326 G > T: p.Arg109Leu and c.614 T > C: p.Val205Ala) and 1 reported mutation in the BMP4 gene among 120 TA probands. The previously reported BMP4 mutation (c.751C > T: p.His251Tyr) was associated with urethra and eye anomalies. By extending the pedigrees, we determined that the tooth phenotypes had an autosomal dominant inheritance pattern, as individuals carrying a BMP4 mutation exhibit different types of dental anomalies. Interestingly, we observed that patients harboring a BMP4 mutation manifested early onset osteopenia or osteoporosis. Further in vitro functional assays demonstrated that two BMP4 mutants resulted in a decreased activation of Smad signaling. Therefore, a loss-of-function in BMP4 may contribute to the clinical phenotypes seen in this study.

CONCLUSIONS

We identified 4 mutations in the BMP4 gene in 120 TA patients. To our knowledge, this is the first study to describe human skeletal diseases associated with BMP4 mutations.

Genetic analysis: Wnt and other pathways in nonsyndromic tooth agenesis

Tooth agenesis (TA) is one of the most common developmental anomalies that affects the number of teeth. An extensive analysis of publicly accessible databases revealed 15 causative genes responsible for nonsyndromic TA, along with their signaling pathways in Wnt/β-catenin, TGF-β/BMP, and Eda/Edar/NF-κB. However, genotype-phenotype correlation analysis showed that most of the causal genes are also responsible for syndromic TA or other conditions. In a total of 198 different mutations of the 15 genes responsible for nonsyndromic TA, 182 mutations (91.9%) are derived from seven genes (AXIN2, EDA, LRP6, MSX1, PAX9, WNT10A, and WNT10B) compared with the remaining 16 mutations (8.1%) identified in the remaining eight genes (BMP4, DKK1, EDAR, EDARADD, GREM2, KREMEN1, LTBP3, and SMOC2). Furthermore, specificity analysis in terms of the ratio of nonsyndromic TA mutations versus syndromic mutations in each of the aforementioned seven genes showed a 98.2% specificity rate in PAX9, 58.9% in WNT10A, 56.6% in MSX1, 41.2% in WNT10B, 31.4% in LRP6, 23.8% in AXIN2%, and 8.4% in EDA. These findings underscore an important role of the Wnt and Wnt-associated pathways in the genetic etiology of this heterozygous disease and shed new lights on the discovery of novel molecular mechanisms associated with tooth agenesis.

The Changing Landscape in the Genetic Etiology of Human Tooth Agenesis

Despite much progress in understanding the genetics of syndromic tooth agenesis (TA), the causes of the most common, isolated TA remain elusive. Recent studies have identified novel genes and variants contributing to the etiology of TA, and revealed new pathways in which tooth development genes belong. Further, the use of new research approaches including next-generation sequencing has provided increased evidence supporting an oligogenic inheritance model for TA, and may explain the phenotypic variability of the condition. In this review, we present current knowledge about the genetic mechanisms underlying syndromic and isolated TA in humans, and highlight the value of incorporating next-generation sequencing approaches to identify causative and/or modifier genes that contribute to the etiology of TA.