The Changing Landscape in the Genetic Etiology of Human Tooth Agenesis

A Novel Ectodysplasin a Gene mutation of X-Linked Hypohidrotic Ectodermal Dysplasia

Introduction

Hypohidrotic ectodermal dysplasia (HED) is a genetic disorder that influences structures of ectodermal origin, such as teeth, hair, and sweat glands. Compared with autosomal recessive and dominant modes of inheritance, the X-linked HED (XLHED) characterized by Hypodontia/Oligodontia teeth, Absent/sparse hair, Anhidrosis/hypohidrosis, and characteristic facial features, is the most frequent and its primary cause is the mutation of ectodysplasin A (EDA) gene. This research aimed to expound the clinical and molecular features of a Chinese male with XLHED and to summarize and compare several previous findings.

Methods

Genomic DNA was obtained from the peripheral blood of the proband and his family members, then Sanger sequencing was used to perform a mutational analysis of EDA. Real-time quantitative PCR and Western blotting were used to detect EDA expression. The transcriptional activity of NF-κB was detected using a luciferase assay.

Results

The probandwith XLHED was identified a novel EDA mutation, c.1119G>C(p.M373I), that affected the molecular analysis of transmembrane protein exon8 mutations, inherited from the mother. He showed a severe multiple-tooth loss, with over 20 permanent teeth missing and sparse hair and eyebrows, dry, thin, and itching skin. Furthermore, his sweating function was abnormal to a certain extent.

Discussion

The functional study showed that this novel mutant led to a significant decrease in the EDA expression level and transcriptional activity of NF-κB. Our findings extend the range of EDA mutations in XLHED patients, which provides the basis and idea for further exploring the pathogenesis of XLHED.

Orodental malformations associated with human MSX1 sequence variants

BACKGROUND

MSX1 sequence variants have been known to cause human tooth agenesis (TA) with or without orofacial clefts. However, their roles during the whole processes of tooth development are not fully understood. This study aimed to characterize a 4-membered family with TA carrying a novel MSX1 pathogenic variant and investigate the disease mechanism.

METHODS

The authors conducted whole exome analysis to define the disease-causing sequence variant. They performed microcomputed tomography, morphometric analyses, transcriptome profiling, and molecular characterization to study the affected teeth and the gene variant.

RESULTS

The authors identified an MSX1 pathogenic variant, p.Glu232∗, in affected family members with TA and concomitant orodental anomalies, namely, prominent maxillary labial frenum, central incisor diastema, median maxillary anterior alveolar cleft, tooth fusion, mandibular molar dysmorphology, thin dentin layer, and slender dental roots. MSX1-defective teeth were not apparently microdontic but had thin dentin layers. The mandibular molars showed a homeotic transformation to maxillary counterparts. Genes involved in extracellular matrix organization and dentinogenesis, such as DMP1 and MMP20, were downregulated in dental pulp tissues of MSX1-defective teeth. The p.Glu232∗-truncated MSX1 properly localized to the nucleus but partially lost its transactivation ability. Analyzing reported cases indicated that truncation sequence variants within the homeobox domain of MSX1 caused a more severe TA phenotype than those outside of the homeobox domain, probably due to dominant negativity compared with haploinsufficiency.

CONCLUSIONS

This study provides in vivo evidence that MSX1 contributes to developmental processes of various orodental tissues in humans.

PRACTICAL IMPLICATIONS

Clinically, hypertrophic labial frenum, incisor diastema, and median maxillary anterior alveolar cleft might be considered diagnostic for MSX1-associated TA.

Compound heterozygous WNT10A missense variations exacerbated the tooth agenesis caused by hypohidrotic ectodermal dysplasia

BACKGROUND

The aim of this study was to analyse the differences in the phenotypes of missing teeth between a pair of brothers with hypohidrotic ectodermal dysplasia (HED) and to investigate the underlying mechanism by comparing the mutated gene loci between the brothers with whole-exome sequencing.

METHODS

The clinical data of the patients and their mother were collected, and genomic DNA was extracted from peripheral blood samples. By Whole-exome sequencing filtered for a minor allele frequency (MAF) ≤0.05 non-synonymous single-nucleotide variations and insertions/deletions variations in genes previously associated with tooth agenesis, and variations considered as potentially pathogenic were assessed by SIFT, Polyphen-2, CADD and ACMG. Sanger sequencing was performed to detect gene variations. The secondary and tertiary structures of the mutated proteins were predicted by PsiPred 4.0 and AlphaFold 2.

RESULTS

Both brothers were clinically diagnosed with HED, but the younger brother had more teeth than the elder brother. An EDA variation (c.878 T > G) was identified in both brothers. Additionally, compound heterozygous variations of WNT10A (c.511C > T and c.637G > A) were identified in the elder brother. Digenic variations in EDA (c.878 T > G) and WNT10A (c.511C > T and c.637G > A) in the same patient have not been reported previously. The secondary structure of the variant WNT10A protein showed changes in the number and position of α-helices and β-folds compared to the wild-type protein. The tertiary structure of the WNT10A variant and molecular simulation docking showed that the site and direction where WNT10A binds to FZD5 was changed.

CONCLUSIONS

Compound heterozygous WNT10A missense variations may exacerbate the number of missing teeth in HED caused by EDA variation.

Pan-cancer analysis reveals the characteristics and roles of tooth agenesis mutant genes

Tooth development is regulated by numerous genes and signaling pathways. Some studies suggest that mutations in these genes may be associated with several cancer types. However, the tooth agenesis mutated genes role in the prognosis and their clinical therapeutic potentials in pan-cancer have not been elaborately explored. Moreover, the intrinsic correlation between tooth agenesis and cancers also needs to be further verified. We preliminarily analyzed expression levels and prognostic values of causative genes of tooth agenesis, and explored the correlation between the expression of tooth agenesis mutated genes and TME, Stemness score, clinical characteristic, immune subtype, and drug sensitivity in pan-cancer, which based on updated public databases and integrated some bioinformatics analysis methods. In addition, we conducted the enrichment analysis of tooth agenesis mutant genes from KOBAS database. We observed that TA mutant genes had significant gene expression differences in multiple cancer types compared with normal tissues. The expression of causative genes of TA is associated with the prognosis in several cancers from different databases. For example, AXIN2 and MSX1 were correlated to the overall survival (OS) of uterine corpus endometrial carcinoma. PAX9 and TP63 were related to OS of lung squamous cell carcinoma. And TP63 was associated with OS in breast invasive carcinoma and pancreatic adenocarcinoma. Furthermore, the expression of TA mutant genes also has a significant correlation with stromal and immune scores, and RNA stemness score and DNA stemness score in pan-cancer. Besides, we observed that all causative genes of TA were significantly correlated with immune subtypes. Moreover, KEGG pathway analysis showed that causative genes of TA were associated with the development and progression of breast cancer, basal cell carcinoma, gastric cancer, and hepatocellular carcinoma. Finally, AXIN2 expression has a significantly positive or negative correlation with drug sensitivity. Our study indicates the great potential of TA mutant genes as biomarkers for prognosis and provides valuable strategies for further investigation of TA mutant genes as potential therapeutic targets in cancers. Our study can further verify that there may be an intrinsic correlation between tooth agenesis and the occurrence of multiple cancers.

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.

Identification of potential key variants in mandibular premolar hypodontia through whole-exome sequencing

Determining genotype-phenotype correlations in patients with hypodontia is important for understanding disease pathogenesis, although only a few studies have elucidated it. We aimed to identify genetic variants linked to non-syndromic bilateral mandibular second premolar hypodontia in a Korean population for the first time by specifying the phenotype of hypodontia. Twenty unrelated individuals with non-syndromic bilateral mandibular second premolar hypodontia were enrolled for whole-exome sequencing. Using a tooth agenesis gene set panel consisting of 112 genes based on literature, potential candidate variants were screened through variant filtering and prioritization. We identified 13 candidate variants in 12 genes, including a stop-gain variant (c.4750C>T) in LAMA3. Through the functional enrichment analysis of the prioritized genes, several terms related to tooth development were enriched in a protein-protein interaction network of candidate genes for mandibular premolar hypodontia. The hypodontia group also had approximately 2-fold as many mutated variants in all four genes related to these key terms, which are CDH1, ITGB4, LAMA3, LAMB3, as those in the 100 healthy control group individuals. The relationship between enriched terms and pathways and mandibular premolar hypodontia was also investigated. In addition, we identified some known oligodontia variants in patients with hypodontia, strengthening the possibility of synergistic effects in other genes. This genetic investigation may be a worthwhile preliminary attempt to reveal the pathogenesis of tooth agenesis and sets a background for future studies.

Genetic and Morphological Variation in Hypodontia of Maxillary Lateral Incisors

(1) Background: Hypodontia has a multifactorial aetiology, in which genetic factors are a major component. Associated with this congenital absence, the formed teeth may show differences in size and shape, which may vary with the specific genetic variants and with the location of the missing teeth. The aims of the present study were to investigate a specific variant of MSX1, derive morphometric tooth measurements in a sample of patients with isolated maxillary lateral incisor agenesis and matched controls, and model the findings. (2) Methods: Genotyping of the MSX1 rs8670 genetic variant and morphometric measurements with a 2D image analysis method were performed for 26 hypodontia patients and 26 matched controls. (3) Results: The risk of upper lateral incisor agenesis was 6.9 times higher when the T allele was present. The morphometric parameters showed significant differences between hypodontia patients and controls and between the unilateral and bilateral agenesis cases. The most affected crown dimension in the hypodontia patients was the bucco-lingual dimension. In crown shape there was significant variation the Carabelli trait in upper first molars. (4) Conclusions: The MSX1 rs8670 variant was associated with variations in morphological outcomes. The new findings for compensatory interactions between the maxillary incisors indicate that epigenetic and environmental factors interact with this genetic variant. A single-level directional complex interactive network model incorporates the variations seen in this study.

Dental management of a pediatric patient with progressive familial intrahepatic cholestasis having dental anomalies: a case report and brief review of the literature

BACKGROUND

Progressive familial intrahepatic cholestasis is a heterogeneous group of disorders, leading to intrahepatic cholestasis, with the possibility of chronic liver failure and biliary cirrhosis. Oligodontia is either the manifestation of a specific syndrome or is non-syndromic. To the best of our knowledge, this is the first case report of type 3 progressive familial intrahepatic cholestasis and concurrent oligodontia, craniosynostosis, dens in dente, taurodontism, and delayed permanent dentition in the medical and dental literature.

CASE PRESENTATION

We present the dental and medical histories and comprehensive dental management of a girl with type 3 progressive familial intrahepatic cholestasis and several dental anomalies, who was referred to a dental clinic due to severe dental caries and pain.

CONCLUSION

Our findings suggest that PFIC with manifestations as oligodontia, craniosynostosis, dens in dente, taurodontism, and delayed permanent dentition, might indicate an unknown syndrome; otherwise, the craniofacial anomalies are the manifestations of an independent disease coinciding with PFIC. Moreover, our case is a good example of the importance of timely medical and dental care in confining further health-related complications. The patient was able to ingest without any pain or discomfort after receiving proper dental management.

Rethinking the Genetic Etiology of Nonsyndromic Tooth Agenesis

PURPOSE OF REVIEW

Genetic studies in humans and animal models have improved our understanding of the role of numerous genes in the etiology of nonsyndromic tooth agenesis (TA). The purpose of this review is to discuss recently identified genes potentially contributing to TA.

RECENT FINDINGS

Despite research progress, understanding the genetic factors underlying nonsyndromic TA has been challenging given the genetic heterogeneity, variable expressivity, and incomplete penetrance of putatively pathogenic variants often observed associated with the condition. Next-generation sequencing technologies have provided a platform for novel gene and variant discoveries and informed paradigm-shifting concepts in the etiology of TA. This review summarizes the current knowledge on genes and pathways related to nonsyndromic TA with a focus on recently identified genes/variants. Evidence suggesting possible multi-locus variation in TA is also presented.

Novel Candidate Genes for Non-Syndromic Tooth Agenesis Identified Using Targeted Next-Generation Sequencing

Non-syndromic tooth agenesis (ns-TA) is one of the most common dental anomalies characterized by the congenital absence of at least one permanent tooth (excluding third molars). Regarding the essential role of genetic factors in ns-TA aetiology, the present study aimed to identify novel pathogenic variants underlying hypodontia and oligodontia. In a group of 65 ns-TA patients and 127 healthy individuals from the genetically homogenous Polish population, the coding sequences of 423 candidate genes were screened using targeted next-generation sequencing. Pathogenic and likely pathogenic variants were identified in 37 (56.92%) patients, including eight nucleotide alternations of genes not previously implicated in ns-TA (CHD7, CREBBP, EVC, LEF1, ROR2, TBX22 and TP63). However, since only single variants were detected, future research is required to confirm and fully understand their role in the aetiology of ns-TA. Additionally, our results support the importance of already known ns-TA candidate genes (AXIN2, EDA, EDAR, IRF6, LAMA3, LRP6, MSX1, PAX9 and WNT10A) and provide additional evidence that ns-TA might be an oligogenic condition involving the cumulative effect of rare variants in two or more distinct genes.

Novel LRP6 Mutations Causing Non-Syndromic Oligodontia

The process of tooth formation is a series of reciprocal interactions between the ectoderm and mesoderm, and it is believed that many genetic factors are involved in this complex process. More than a dozen genes have been identified in non-syndromic tooth agenesis; however, the genetic etiology underlying tooth agenesis is not fully understood yet. In this study, we identified two novel LRP6 mutations in two non-syndromic oligodontia families. Both probands had 16 and 17 missing teeth in their permanent dentition. Mutational analysis identified a de novo frameshift mutation by a 1-bp insertion in exon 9 (NM_002336.2: c.1870dupA, p.(Met624Asnfs*29)) and a splicing donor site mutation in intron 8 (c.1762+2T>C). An in vitro splicing assay confirmed the deletion of exon 8, and the deletion would result in a frameshift. Due to the premature termination codons introduced by the frameshift, both mutant transcripts would be degraded by nonsense-mediated mRNA decay, resulting in haploinsufficiency.

Novel Dental Anomaly-associated Mutations in WNT10A Protein Binding Sites

OBJECTIVE

WNT/β-catenin signaling is initiated by binding of a WNT protein to a Frizzled (FZD) receptor and a co-receptor, low-density lipoprotein (LDL) receptor-related protein 5 or 6 (LRP5/6). The objective of this study was to find the genetic variants responsible for dental anomalies found in 4 families.

METHODS

Clinical and radiographic examination and whole exome sequencing were performed on 5 patients affected with dental anomalies and the mutant proteins modeled.

RESULTS

Five patients were heterozygous for the WNT10A variants, including c.877C>T; p.Arg293Cys, c.874A>G; p.Ser292Gly, c.1042C>T; p.Arg348Cys, and c.1039G>T; p.347GluX. The p.Arg293Cys and p.Ser292Gly mutations are located in the WNT10A N-terminal domain region with binding sites for FZD receptor, porcupine, WNTLESS, and extracellular binding proteins, so they are likely to have adverse effects on binding these proteins. The p.Arg348Cys mutation, which is located in the binding site of LRP5/6 co-receptors, is postulated to result in impaired binding to these co-receptors. The nonsense mutation p.347GluX is predicted to result in the truncation of most of the C-terminal domain, which is likely to disrupt the binding of WNT10A to WNTLESS, the membrane protein that binds lipid-acylated WNT proteins to carry them from the endoplasmic reticulum to the cell surface and FZD.

CONCLUSIONS

Four novel mutations in WNT10A were identified in patients with isolated tooth agenesis. The mutations in the N-terminal domain and the interface between the N- and C-terminal domains of WNT10A in our patients are likely to disrupt its binding with FZD, LRP5/6, and various other proteins involved in WNT10A processing and transport, impair WNT and SHH signaling, and subsequently result in tooth agenesis, microdontia, and root maldevelopment.

Dental anomalies in non-syndromic orofacial clefts: a clinical approach

Orofacial clefts (OC) represent some of the most common congenital malformations and affect multiple structures in the craniofacial region. There are a wide range of morphological OC types within the spectrum of both non-syndromic OC (NSOC) and syndromic OC, including cleft lip (CL); cleft lip and palate (CLP) and cleft palate (CP). Here, we describe the most frequent dental anomalies seen in the permanent dentition of individuals with NSOC, comparing them between the three main cleft types (CL, CLP, CP). We present these findings from the perspective of prevalence relating to each anomaly, as well as the clinical characteristics and potential impact in the rehabilitation process. The investigation of dental anomalies associated with NSOC is important, helping to expand the phenotypic characterization of NSOC, improve initial diagnostics and establish appropriate rehabilitation and counseling.

Number of Teeth Is Related to Craniofacial Morphology in Humans

Simple Summary

In modern humans, congenital absence of one or more permanent teeth has a prevalence of 22.6% when considering the third molars and of 6.4% when not. Its high prevalence, in conjunction with evolutionary findings pinpointing to a steady reduction in teeth number, raises the question whether the congenital absence of teeth in modern humans is an evolutionary trend rather than an anomaly. Previous studies have shown that modern humans with less teeth also have smaller faces; however, the association between teeth number and craniofacial morphology remains unclear. Here, we show that less teeth are associated with a flatter profile and a decreased facial height. These findings support the claim of a broader relationship between number of teeth and overall craniofacial development and have evolutionary implications, since face reduction comprises also an evolutionary trend in humans.

Abstract

One of the most common dental anomalies in humans is the congenital absence of teeth, referred to as tooth agenesis. The association of tooth agenesis to craniofacial morphology has been previously investigated but remains unclear. We investigated this association by applying geometric morphometric methods in a large sample of modern humans. In line with previous studies, we report here that a reduced teeth number is linked to a less convex profile, as well as to a shorter face. The effects were similar for males and females; they increased as the severity of the tooth agenesis increased and remained unaltered by the inclusion of third molars and of allometry in the analysis. Furthermore, in cases with tooth agenesis only in the maxilla, there was no detectable effect in mandibular shape, whereas maxillary shape was affected independently of the location of missing teeth. The robustness of the present sample along with the shape analysis and the statistical approach applied, allowed for thorough testing of various contributing factors regarding the presence but also the magnitude of effects. The present findings suggest a relationship between number of teeth and overall craniofacial development and have evolutionary implications.

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.

Detection of a rare AXIN2 variant in an Iranian family with hypodontia and oligodontia

Background. Hypodontia, or the absence of one or more teeth during tooth formation, is a highly prevalent dental anomaly. Nevertheless, the main causes are still unknown. Mutations in PAX9, MSX1, WNT10A, and AXIN2 genes are most commonly associated with non-syndromic tooth agenesis in the literature. This study investigated these candidate genes in an Iranian family with non-syndromic hypodontia and oligodontia. Methods. Peripheral blood samples of the proband and her family members were collected, and DNA extractions using the salting-out method were carried out. In addition, polymerase chain reaction (PCR) and Sanger sequencing for candidate genes were performed. Results. A missense variant (rs4904210) was identified in the PAX9 gene, with one heterozygous missense variant (rs2240308) and one stop-gained variant (rs121908568) in the AXIN2 gene. Conclusion. By surveying similar studies and analyzing the variant in bioinformatics websites, we concluded that the heterozygous stop-gained variant rs121908568 in exon 8 of the AXIN2 gene could be responsible for tooth agenesis in the Iranian population.

Prevalence of KRAS, PIK3CA, BRAF and AXIN2 gene mutations in colorectal cancer and its relationship with dental agenesis: a systematic review

Introduction: The study of allelic and genotypic frequencies contributes to determining the distribution of genetic variants in different populations and their possible association with biomarkers. This knowledge could improve the decision-making process regarding the management of some diseases such as colorectal cancer (CRC), in which the detection of clinical biomarkers such as dental agenesis could be crucial in clinical practice. Objective: To evaluate the available scientific evidence on the prevalence of KRAS, PIK3CA, BRAF and AXIN2 mutations and their possible association with dental agenesis in people with CRC. Materials and methods: A systematic search was conducted in PubMed, EMBASE and Cochrane Library databases using the following search strategy: type of studies: observational studies reporting the prevalence of KRAS, PIK3CA, BRAF and AXIN2 mutations in people diagnosed with CRC and their possible association with dental agenesis; publication language: English and Spanish; publication period: 2010-2020; search terms: “Genes”, “RAS”, “Kras”, “PIK3CA”, “BRAF”, “AXIN2”, “Mutation”, “Polymorphism”, “Colorectal Neoplasms”, “Colorectal Cancer”, used in different combinations (“AND” and “OR”).   Results: The initial search yielded 403 records, but only 30 studies met the eligibility criteria. Of these, 11, 5, 5 and 1 only reported the prevalence of PIK3CA, KRAS, BRAF and AXIN2 mutations, respectively; while 8 reported the prevalence of more than one of these mutations in patients with CRC. The prevalence of KRAS (p.Gly12Asp), PIK3CA (p.Glu545Lys), and BRAF (p.Val600Glu) mutations ranged from 20.5% to 54%, 3.5% to 20.2%, and 2.5% to 12.1%, respectively. There were no findings regarding the association between the occurrence of these mutations and dental agenesis.   Conclusions: KRAS mutations were the most prevalent; however, there is no evidence on the association between dental agenesis and the occurrence of KRAS, PIK3CA and BRAF germline mutations in individuals with CRC.

Synergistic Mutations of LRP6 and WNT10A in Familial Tooth Agenesis

Familial tooth agenesis (FTA), distinguished by developmental failure of selected teeth, is one of the most prevalent craniofacial anomalies in humans. Mutations in genes involved in WNT/β-catenin signaling, including AXIN2 WNT10A, WNT10B, LRP6, and KREMEN1, are known to cause FTA. However, mutational interactions among these genes have not been fully explored. In this study, we characterized four FTA kindreds with LRP6 pathogenic mutations: p.(Gln1252*), p.(Met168Arg), p.(Ala754Pro), and p.(Asn1075Ser). The three missense mutations were predicted to cause structural destabilization of the LRP6 protein. Two probands carrying both an LRP6 mutant allele and a WNT10A variant exhibited more severe phenotypes, suggesting mutational synergism or digenic inheritance. Biallelic LRP6 mutations in a patient with many missing teeth further supported the dose-dependence of LRP6-associated FTA. Analysis of 21 FTA cases with 15 different LRP6 loss-of-function mutations revealed high heterogeneity of disease severity and a distinctive pattern of missing teeth, with maxillary canines being frequently affected. We hypothesized that various combinations of sequence variants in WNT-related genes can modulate WNT signaling activities during tooth development and cause a wide spectrum of tooth agenesis severity, which highlights the importance of exome/genome analysis for the genetic diagnosis of FTA in this era of precision medicine.

Research algorithm for the detection of genetic patterns and phenotypic variety of non-syndromic dental agenesis

Introduction: Dental agenesis (DA), brings together the anodontia, oligodontia, hypodontia, characterized by a deficit in the development of a variable number of teeth. The objectives of the study were to illustrate the phenotypic variability of non-syndromic DA, to identify cases of DA with hereditary genetic transmission, and establish the mode of DA genetic pattern in these cases, together with the determination of DA prevalence in the population group study. Patients, Materials and Methods: The cross-sectional observational study was performed on a mixed population group, consisting of 861 Caucasian patients, between January 2018–December 2019. The clinical evaluation protocol of patients with DA, used to illustrate their phenotype, included the following stages: oral examination, photographic examination, and radiological examination. The evaluation protocol specific to the family genetic study of patients with DA, involved the following three stages: family survey, construction of the family tree and analysis of the pedigree structure. Results: The prevalence of DA in the population group was 2.78%. Regarding the phenotype, DA mainly affected the upper arch (50% of cases); bilateral DA had a significantly increased incidence (83.33% of cases) compared to unilateral form; in most cases (75%), a patient lacked one to two teeth, the lack of two teeth being the most common form (83.33% of cases); the upper lateral incisors were the teeth most frequently involved in DA (31.11% of the total missing teeth). Regarding the family genetic study, hereditary DA with autosomal dominant inheritance was present in 37.50% of cases. In the other cases (62.50%), isolated, sporadic forms of DA were registered, suggesting a spontaneous de novo mutation or a disorder of odontogenesis of a non-genetic nature. Conclusions: We consider that this study is of interest for current scientific research with applicability in dental medicine, by bringing actual information on the prevalence of non-syndromic DA in South-East Romania, the variety of phenotypic spectrum of DA for this geographic area, and the role of heredity in the DA genetic determinism in the studied population.

Use of a Modified Nance Appliance for Esthetic Rehabilitation of a Child Patient with Rare Nonfamilial and Nonsyndromic Oligodontia

Congenital absence of more than 6 teeth except the third molar is known as oligodontia. It can affect both primary and permanent dentitions. The affected individuals usually demonstrate esthetic, functional, and psychological concerns. The present case report is about a 4-year-old female patient with multiple missing (both primary and permanent) teeth with esthetic and social problems. On extraoral examination, the patient demonstrated upper lip relapse due to missing anterior teeth. On physical examination, no other abnormality was detected in relation to the hair, appendages, or presence of a cleft. On intraoral and radiographic examination, 21 teeth were missing, which included both the primary and the permanent tooth buds. To encourage a positive behavioral change, it was decided to carry out prosthetic intervention using a modified fixed Nance appliance and acrylic teeth. After the replacement of the missing teeth, a marked improvement in the profile and esthetics was seen.

Third Molar Agenesis Is Associated with Facial Size

Simple Summary

Missing third molars is a common occurrence in modern humans with a prevalence of approximately 20% in the general population. The absence of those teeth, however, is not found in other human predecessors. Therefore, there is speculation whether the congenital absence of third molars is part of an evolutionary mechanism that leads to smaller jaws, smaller and fewer teeth, or if their absence is associated with more local developmental factors. In this study, we assessed the size of the cranial base, the maxilla, the mandible and the entire craniofacial complex in individuals missing one or more third molars and compared them with a group with no missing teeth. We showed that in cases with one or more missing third molars, there is a significant decrease in the size of the maxilla, the mandible as well as the entire facial configuration. Additionally, the more missing third molars, the smaller the jaws and the face were. These findings suggest that isolated third molar agenesis is part of a developmental mechanism related to craniofacial size reduction. Whether this mechanism is part of an evolutionary process in humans remains to be seen.

Abstract

Individuals with congenitally missing permanent teeth, other than third molars, present smaller craniofacial configurations compared to normal controls. However, it is not known if agenesis of third molars is part of the same mechanism. Therefore, this study assessed individuals with and without isolated third molar agenesis and tested the relation of this condition to the size of their facial configurations, using geometric morphometric methods. We show that the absence of one or more third molars is associated with a smaller maxilla, smaller mandible and a smaller overall facial configuration. The effect was larger as the number of missing third molars increased. For example, the size of the mandibular centroids in five 16-year-old females with no, one, two, three or four missing third molars showed a size reduction of approximately 2.5 mm per missing third molar. In addition, in cases with third molar agenesis in one jaw only, the effect was also evident on the opposite jaw. Our findings suggest that isolated third molar agenesis is part of a developmental mechanism resulting also in craniofacial size reduction. This might be the effect of an evolutionary process observed in humans, leading to fewer and smaller teeth, as well as smaller facial structures.

Aesthetic Parameters and Patient-Perspective Assessment Tools for Maxillary Anterior Single Implants

Background

This review aimed to concisely describe the current aesthetic objective indices for a single-implant maxillary anterior crown. The secondary aim was to propose introducing a unified, standardized questionnaire for adequately collecting patient-reported outcome measures (PROMs) in implant dentistry.

Materials and Methods

A literature review was conducted using both EMBASE/Ovid and MEDLINE/PubMed databases by combining keywords and Emtree/Mesh terms related to “Esthetics,” “Self-Assessment or Surveys and Questionnaires,” and “Single-Tooth Dental Implants.”

Results

The most meaningful aesthetic objective indices for single implants in the literature are the Pink Esthetic Score (PES), the Papilla Presence Index (PPI), Peri‐Implant and Crown Index (PICI), PES/White Esthetic Score (PES/WES), the Implant Crown Aesthetic Index (ICAI), and a modified version of the ICAI (mod-ICAI) index. Clearly, PES/WES is still the most widely accepted tool. It is encouraging to observe that there is an increasing tendency in recent years to report PROMs more frequently in the implant dentistry literature. We proposed the implementation of a unified, standardized questionnaire using a self-administered visual analogue scale (VAS) scoring system, which evaluates overall satisfaction, comfort, tooth appearance, gingival appearance, function, and hygiene complexity. This tool should be validated in the oral implantology research context for its regular implementation or further development.

Conclusions

Conducting qualitative studies among dental implant patients who received few implants or single-tooth implant reconstructions in the aesthetic zone may help dental researchers understand better how to efficiently develop and validate a quantitative instrument. This standard tool would reduce heterogeneity bias by providing comparable data between studies.

Functional characterization of ATF1, GREM2 AND WNT10B variants associated with tooth agenesis

OBJECTIVE

To determine the functional effects of ATF1, WNT10B and GREM2 gene variants identified in individuals with tooth agenesis (TA).

SETTINGS AND SAMPLE POPULATION

Stem cells from human exfoliated deciduous teeth (SHED) were used as an in vitro model system to test the effect of TA-associated variants.

MATERIALS AND METHODS

Plasmid constructs containing reference and mutant alleles for ATF1 rs11169552, WNT10B rs833843 and GREM2 rs1414655 variants were transfected into SHED for functional characterization of variants. Allele-specific changes in gene transcription activity, protein expression, cell migration and proliferation, and expression of additional tooth development genes (MSX1, PAX9 and AXIN2) were evaluated. Data analyses were performed using Student's t-test. P-values ≤ .05 were considered statistically significant.

RESULTS

Mutant variants resulted in significantly decreased transcriptional activity of respective genes (P < 0.05), although no changes in protein localization were noted. Expression of MSX1 was significantly decreased in ATF1- and GREM2-mutant cells, whereas PAX9 or AXIN2 mRNA expression was not significantly altered. Mutant WNT10B had no significant effect on the expression of additional TA genes. ATF1- and GREM2-mutant cells presented increased cell migration. Cell proliferation was also affected with all three mutant alleles.

CONCLUSIONS

Our results demonstrate that ATF1, WNT10B and GREM2 mutant alleles have modulatory effects on gene/protein function that may contribute to TA.

Pax9's Interaction With the Ectodysplasin Signaling Pathway During the Patterning of Dentition

In these studies, we explored for the first time the molecular relationship between the paired-domain-containing transcription factor, Pax9, and the ectodysplasin (Eda) signaling pathway during mouse incisor formation. Mice that were deficient in both Pax9 and Eda were generated, and the status of dentition analyzed in all progeny using gross evaluation and histomorphometric means. When compared to wildtype controls, Pax9^+/–Eda^–/– mice lack mandibular incisors. Interestingly, Fgf and Shh signaling are down-regulated while Bmp4 and Lef1 appear unaffected. These findings suggest that Pax9-dependent signaling involves the Eda pathway and that this genetic relationship is important for mandibular incisor development. Studies of records of humans affected by mutations in PAX9 lead to the congenital absence of posterior dentition but interestingly involve agenesis of mandibular central incisors. The latter phenotype is exhibited by individuals with EDA or EDAR mutations. Thus, it is likely that PAX9, in addition to playing a role in the formation of more complex dentition, is also involved with EDA signaling in the initiation of odontogenesis within the incisal domain.

Functional Effects of WNT10A Rare Variants Associated with Tooth Agenesis

Mutations in WNT10A have frequently been reported as etiologic for tooth agenesis (TA). However, the effects of WNT10A variation on gene/protein function and contribution to TA phenotypes remain poorly understood. Here, we performed bioinformatic and functional characterization analysis of WNT10A variants. In silico prediction of variant function was performed with VIPUR for all WNT10A missense variants reported in the Exome Aggregation Consortium database. Functional characterization experiments were then performed for selected WNT10A variants previously associated with TA. Expression vectors for wild-type and mutant WNT10A were made and transfected into stem cells from human exfoliated deciduous teeth (SHED) for evaluation of gene/protein function, WNT signaling activity, and effects on expression of relevant genes. While 75% of WNT10A variants were predicted neutral, most of the TA-associated variants received deleterious scores by potentially destabilizing or preventing the disulfide bond formation required for proper protein function. WNT signaling was significantly decreased with 8 of 13 variants tested, whereas wild-type-like activity was retained with 4 of 13 variants. WNT10A-mutant cells (T357I, R360C, and R379C mutants) showed reduced or impaired binding affinity to FZD5, suggesting a potential mechanism for the decreased WNT signaling. Mutant cells also had decreased WNT10A protein expression in comparison to wild-type cells. mRNA expression of PAX9, MSX1, AXIN2, and RUNX2 (known tooth development genes) was perturbed in mutant cells and quite significantly for PAX9 and RUNX2. Transcriptome analysis of wild-type and T357I-mutant cells identified 36 differentially expressed genes (26 downregulated, 10 upregulated) involved in skeletal system development and morphogenesis and pattern specification. WNT10A variants deemed pathogenic for TA likely affect protein folding and/or stabilization, leading to decreased WNT signaling and concomitant dysregulated expression of relevant genes. These findings may allow for improved interpretation of TA phenotypes upon clinical diagnosis while providing important insights toward the development of future tooth replacement 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.

A novel missense mutation of LRP6 identified by whole-exome sequencing in a Chinese family with non-syndromic tooth agenesis

OBJECTIVE

The aim of this study was to explore the genetic basis of non-syndromic tooth agenesis (TA) in a Chinese family of five individuals using whole-exome sequencing (WES) analysis.

SETTINGS AND SAMPLE POPULATION

Five participants/Family-based study of a non-syndromic TA proband.

METHODS

The proband, proband's mother and grandmother displayed congenital tooth deficiency. Genomic DNA was extracted from the peripheral blood or saliva samples of the proband, her parents and her grandmother, and WES was utilized to identify the causal genetic mutation. The identified mutation was further verified by Sanger sequencing and analysed using bioinformatics tools.

RESULTS

A novel missense mutation, c.G711T (p.L237F), was identified in the low-density lipoprotein receptor-related protein 6 (LRP6) gene in all affected individuals. Bioinformatics analysis predicted the mutation to be deleterious, with the mutant LRP6 protein displaying a tertiary structural change that might disturb the Wnt/β-catenin signalling pathway.

CONCLUSIONS

The identification of the mutation in the LRP6 gene and autosomal dominant inheritance with TA in the generations is consistent with the mutation being responsible for TA in the family, and furthers the association of LRP6 with nonsyndromic TA.

Number of teeth is associated with facial size in humans

During human evolution there has been an increase in the size of the brain and the cranium, whereas the size of the face, as well as the size and number of teeth have decreased. In modern humans, the occurrence of missing permanent teeth, namely tooth agenesis, is common. It could be attributed to a biological mechanism of tooth number reduction that has evolved during time and might still be active. Although, if evident, it would add support to this theory, the relationship between this phenotype and craniofacial size remains largely unknown. The present case-control study shows that modern individuals with tooth agenesis have indeed smaller facial configurations. For example, a 15-year-old female with no, one, or ten missing teeth would have a facial centroid size of 511.83, 510.81, or 501.70 mm, respectively. No such effect was observable in the cranial base and the cranium. Our results suggest that common gene regulatory mechanisms that have evolved over time, continue to regulate the number of teeth and facial size of modern humans in a coordinated manner. We anticipate our findings to enrich our understanding of the evolution and development of the human head and kindle future developmental research on this field.

Identification of Disease Risk DNA Variations is Shaping the Future of Precision Health

In recent years, the knowledge generated by decoding the human genome has allowed groundbreaking genetic research to better understand genomic architecture and heritability in healthy and disease states. The vast amount of data generated over time and yet to be generated provides the basis for translational research towards the development of preventive and therapeutic strategies for many conditions. In this special issue, we highlight the discoveries of disease-associated and protective DNA variations in common human diseases and developmental disorders.

Management of patients with hypodontia: What has changed?

This review will consider changes in clinical practice associated with the management of patients with missing teeth and briefly review the evidence base that underpins what we do for them.

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.

Tooth agenesis-related GLI2 and GLI3 genes may contribute to craniofacial skeletal morphology in humans

OBJECTIVE

The present cross-sectional, multi-centre, genetic study aimed to determine, whether single nucleotide polymorphisms (SNPs) in tooth agenesis (TA)-associated GLI2 and GLI3 genes contribute to the development of craniofacial skeletal morphology in humans.

DESIGN

Orthodontic patients from an ethnically heterogeneous population were selected for the present study (n = 594). The presence or absence of TA was determined by analysis of panoramic radiography and dental records. The subjects were classified according to their skeletal malocclusion and facial growth pattern by means of digital cephalometric analysis. Genomic DNA was extracted from squamous epithelial cells of the buccal mucosa and SNPs in GLI2 (rs3738880, rs2278741) and GLI3 (rs929387, rs846266) were analysed by polymerase chain reaction using TaqMan chemistry and end-point analysis.

RESULTS

Class II skeletal malocclusion presented a significantly lower frequency of TA (P < 0.05). Subjects without TA showed significantly higher ANB angles (P < 0.05). Genotype and/or allele distributions of the SNPs in GLI2 (rs3738880, rs2278741) and GLI3 (rs846266) were associated with the presence of TA (P < 0.05). The SNPs rs3738880, rs2278741 and rs929387 were also associated with some type of skeletal malocclusion (P < 0.05), but not with the facial growth pattern (P > 0.05). The G allele for TA-related GLI2 rs3738880 was strongly linked to the presence of Class III skeletal malocclusion (OR = 2.03; 95% CI = 1.37-3.03; P<3125 × 10^-6). GLI2 rs2278741 C allele was overrepresented in individuals without TA, suggesting it as a protective factor for this dental phenotype (OR = 0.43; 95% CI = 0.24-0.78; P<625 × 10^-5).

CONCLUSION

The present study suggests that SNPs in TA-associated GLI2 and GLI3 genes may also play a role in the development of skeletal malocclusions. rs3738880 and rs2278741 in GLI2 seems to contribute to the genetic background for skeletal Class III and TA, respectively. TA could be an additional predictor of craniofacial morphology in some cases. Further research replicating the reported associations should be performed.

Non-syndromic cleft lip with or without palate susceptible loci is associated with tooth agenesis

OBJECTIVE

Non-syndromic tooth agenesis (NSTA) may share common genetic factors with non-syndromic cleft lip with or without cleft palate (NSCL/P). Single-nucleotide polymorphisms (SNPs) were associated with individual's susceptibility to these anomalies. We selected five NSCL/P-associated SNPs from our previous genome-wide association study (GWAS) to test for the associations with NSTA.

MATERIALS AND METHODS

A total of 677 NSTA cases and 1,144 healthy controls were recruited in this case-control study. Five genome-wide NSCL/P-associated SNPs (rs2235371, rs7078160, rs8049367, rs4791774, and rs13041247) were genotyped by TaqMan platform and evaluated for the associations with NSTA using plink software.

RESULTS

No significant associations between these SNPs and risk of NSTA were observed in the overall analysis and subgroup analysis with the number of missing teeth. However, in the subgroup analysis by tooth position, rs8049367 was nominally associated with mandibular premolar agenesis (Dominant model: OR_dom  = 0.66, 95% CI_dom  = 0.47-0.93, p_dom  = 0.016; Heterozygote model: OR_het  = 0.60, 95% CI_het  = 0.41-0.88, P_het  = 0.008). Rs4791774 showed a nominal association with congenitally missing maxillary canine (Dominant model: OR_dom  = 0.53, 95% CI_dom  = 0.28-0.98, p_dom  = 0.041; Heterozygote model: OR_het  = 0.50, 95% CI_het  = 0.26-0.97, P_het  = 0.041) and premolar (Additive model: OR = 0.59, 95% CI = 0.36-0.96, p = 0.035).

CONCLUSION

This study showed that NSCL/P susceptible loci rs8049367 and rs4791774 were probably associated with the risk of NSTA.