Familial Tooth Agenesis Research Articles

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.

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.

A novel mutation of MSX1 in oligodontia inhibits\xa0odontogenesis of dental pulp stem cells via the ERK pathway

BackgroundTooth agenesis, one of the most common developmental anomalies, can affect the function and esthetics of patients. The aim of the present study was to identify genetic clues for familial tooth agenesis and explore the underlying mechanisms, focusing on the role of human dental pulp stem cells (hDPSCs).MethodsWe applied Sanger sequencing to identify the cause of oligodontia in a Chinese family. DNA transfection and functional analysis in DPSCs was also performed to explore the impact of the identified mutation on this phenotype.ResultsIn this study, a novel frameshift mutation, the twenty-nucleotide deletion (c.128_147del20, p.Met43Serfsx125), in exon1 of MSX1 was detected in a Chinese family causing autosomal dominant nonsyndromic oligodontia. The mutation cosegregated with the tooth agenesis phenotype in this family. DPSCs transfected with mutant MSX1 plasmid showed decreased capacity of osteo/odontogenic differentiation with a lower expression level of dentin sialophosphoprotein (DSPP) and bone sialoprotein (BSP) compared with those transfected with control MSX1 plasmid. Mechanically, control MSX1 showed nuclear localization while the mutant MSX1 inhibited its nuclear translocation and localized on the cytoplasm to inhibit ERK phosphorylation. Furthermore, we inhibited the ERK pathway using ERK inhibitor (U0126) treatment in control MSX1-transfected DPSCs which could downregulate mineralized nodule formation and the expression of odontogenic genes.ConclusionWe demonstrated a novel MSX1 mutation causing familial nonsyndromic oligodontia and mechanically MSX1 regulates odontogenesis through the ERK signaling pathway in human dental pulp stem cells.

Whole-Exome Sequencing Identifies Novel Variants for Tooth Agenesis

Tooth agenesis is a common craniofacial abnormality in humans and represents failure to develop 1 or more permanent teeth. Tooth agenesis is complex, and variations in about a dozen genes have been reported as contributing to the etiology. Here, we combined whole-exome sequencing, array-based genotyping, and linkage analysis to identify putative pathogenic variants in candidate disease genes for tooth agenesis in 10 multiplex Turkish families. Novel homozygous and heterozygous variants in LRP6, DKK1, LAMA3, and COL17A1 genes, as well as known variants in WNT10A, were identified as likely pathogenic in isolated tooth agenesis. Novel variants in KREMEN1 were identified as likely pathogenic in 2 families with suspected syndromic tooth agenesis. Variants in more than 1 gene were identified segregating with tooth agenesis in 2 families, suggesting oligogenic inheritance. Structural modeling of missense variants suggests deleterious effects to the encoded proteins. Functional analysis of an indel variant (c.3607+3_6del) in LRP6 suggested that the predicted resulting mRNA is subject to nonsense-mediated decay. Our results support a major role for WNT pathways genes in the etiology of tooth agenesis while revealing new candidate genes. Moreover, oligogenic cosegregation was suggestive for complex inheritance and potentially complex gene product interactions during development, contributing to improved understanding of the genetic etiology of familial tooth agenesis.

Association of AXIN2 gene polymorphisms with nonsyndromic oligodontia in Turkish families

Tooth agenesis is the most common developmental abnormality of the human dentition characterized by the congenital absence of one or more permanent teeth. Oligodontia is the term used to describe severe tooth agenesis, where six or more permanent teeth are missing. The WNT gene pathway regulates multiple developmental processes during craniofacial and tooth development, and variations in WNT pathway genes have been reported in individuals with tooth agenesis. In this study, we investigated the association of 37 SNPs in/nearby 12 WNT pathway genes (WNT3, WNT3A, WNT5A, WNT8A, WNT9B, WNT10A, WNT11, AXIN1, AXIN2, APC, LRP5, LRP6) with oligodontia in 22 multiplex families. Genotypes were generated using Taqman chemistry in a real-time polymerase chain reaction assay. Family-based association tests were performed using FBAT. Pairwise-haplotype analysis was also performed. Bonferroni correction was used to adjust for multiple testing and P-values ≤ 0.001 were considered statistically significant. We found nominal association for AXIN2 rs7591, located in the 3’ UTR, with oligodontia (P=0.04). In silico analysis of SNP function predicted a binding site for miR-205 with potential impact on AXIN2 expression. Although modest, these results continue to support a role for AXIN2 in the etiology of familial tooth agenesis.

Bilateral taurodontism in primary and permanent molars associated with hypodontia

The article is to present a case of bilateral taurodontism in primary and permanent molars associated with hypodontia and to discuss the endodontic aspects. Taurodontism in permanent molars are most commonly affected and it has a very low incidence, and very fewer cases are reported in the literature in the deciduous dentition. A 12-year-old boy presented with irregularly placed tooth in upper right back region of the jaw. Orthopantomogramrevealed taurodontism in seven teeth including both primary and permanent teeth, associated with congenitally missing three premolars and permanent mandibular central incisors. Taurodontism is more frequent in nonsyndromic familial tooth agenesis. Individuals in families with second premolar and molar oligodontia are more likely to have taurodontism. Since there is a wide variation in size and shape of pulp chamber with varying degree of obliteration and canal configuration, root canal therapy becomes a challenge so it is essential to recognize and render preventive care for these teeth.

Identification and characterization of disease causing genetic variant by conventional genotyping and whole genome sequencing in familial tooth agenesis

Background Congenital tooth agenesis (CTA), a type of craniofacial disorders affects approximately 20% (including 3 molar or Wisdom teeth) and 2-10% (excluding 3 molar) of the world population. Five major candidate genes known to be associated with syndromic and non-syndromic CTA, these are PAX9, MSX1, AXIN2, EDA and WNT10A. The present investigation was undertaken to identify and characterize disease causing genetic variant by conventional genotyping and whole genome sequencing in familial tooth agenesis

Solitary bone cyst coexistent with tooth agenesis: Unique case report and brief review

Solitary bone cysts (SBCs) exist generally as asymptomatic solitary lesions and have no epithelial lining. They are uncommon in the jaws and are often polymorphic, show scalloped borders when located between the roots. They have higher predilection for the posterior mandible, mostly occurring near the mental foramen. Various pathomechanisms were proposed, but the triggering factor still remains to be ascertained. Currently, osteolytic pathogenesis is speculated, which may be due to vascular alteration leading to aseptic osseous necrosis. Fibro-osseous lesions are occasionally associated with SBCs, but concomitant presence with tooth agenesis has not been reported. We present a unique case of SBC with familial tooth agenesis in a 16-year-old female patient with a brief review.

Bilateral taurodontism in primary and permanent molars associated with hypodontia

The aim of this article is to present a case of bilateral taurodontism in the primary and permanent molars associated with hypodontia and to discuss the endodontic aspects. Taurodontism in the permanent molars are most commonly affected, and it has a very low incidence and very few cases are reported in the literature in deciduous dentition. A 12-year-old boy presented with irregularly placed tooth in the upper right back region of his jaw. Orthopantamogram revealed taurodontism in seven teeth, including both primary and permanent teeth, associated with congenitally missing three premolars and permanent mandibular central incisors. Taurodontism is more frequent in non-syndromic familial tooth agenesis. Individuals in families with second premolar and molar oligodontia are more likely to have taurodontism. Because there is a wide variation in size and shape of pulp chamber with a varying degree of obliteration and canal configuration, root canal therapy becomes a challenge and, therefore, it is essential to recognize and render preventive care for these teeth.

Novel PAX9 and COL1A2 missense mutations causing tooth agenesis and OI/DGI without skeletal abnormalities.

Inherited dentin defects are classified into three types of dentinogenesis imperfecta (DGI) and two types of dentin dysplasia (DD). The genetic etiology of DD-I is unknown. Defects in dentin sialophosphoprotein (DSPP) cause DD type II and DGI types II and III. DGI type I is the oral manifestation of osteogenesis imperfecta (OI), a systemic disease typically caused by defects in COL1A1 or COL1A2. Mutations in MSX1, PAX9, AXIN2, EDA and WNT10A can cause non-syndromic familial tooth agenesis. In this study a simplex pattern of clinical dentinogenesis imperfecta juxtaposed with a dominant pattern of hypodontia (mild tooth agenesis) was evaluated, and available family members were recruited. Mutational analyses of the candidate genes for DGI and hypodontia were performed and the results validated. A spontaneous novel mutation in COL1A2 (c.1171G>A; p.Gly391Ser) causing only dentin defects and a novel mutation in PAX9 (c.43T>A; p.Phe15Ile) causing hypodontia were identified and correlated with the phenotypic presentations in the family. Bone radiographs of the proband’s dominant leg and foot were within normal limits. We conclude that when no DSPP mutation is identified in clinically determined isolated DGI cases, COL1A1 and COL1A2 should be considered as candidate genes. PAX9 mutation p.Phe15Ile within the N-terminal β-hairpin structure of the PAX9 paired domain causes tooth agenesis.

Novel missense mutation in PAX9 gene associated with familial tooth agenesis

PAX9 is a transcription factor deeply involved in the gene networks that regulate odontogenesis. To date, only a restricted number of mutations in this gene have been associated with non-syndromic tooth agenesis. Six families segregating non-syndromic oligodontia/hypodontia were screened for mutations in PAX9 gene. A novel missense mutation lying in the exon 2 close to the end of the paired domain in three families was identified. Heterozygous mutation C503G is expected to result in an alanine-to-glycine amino acid change in residue 168 (Ala168Gly), which is invariably conserved among several species. The alanine-glycine change might lead to protein structural alteration because of the unique flexibility properties of glycine. Three mutations in intron 2 were also detected. Variations IVS2-109G>C, IVS2-54A>G, and IVS2-41A>G were identified in both affected and unaffected members of the sample; however, these polymorphic variants may be involved in the phenotype as one proband showing all three intronic mutations in homozygosis was affected with the most severe oligodontia within the sample.

Taurodontism in Brazilian patients with tooth agenesis and first and second-degree relatives: A case–control study

AimAn association between tooth agenesis and taurodontism has been suggested. To verify if tooth agenesis and taurodontism are associated within families and specific patterns of tooth agenesis, this study aims to compare the frequency of taurodontism in patients with nonsyndromic familial tooth agenesis, their first and second-degree relatives with complete permanent dentition and a control group of unrelated healthy individuals with complete permanent dentition. Materials and methodsPanoramic radiographs of patients with nonsyndromic familial tooth agenesis, their first and second-degree relatives and a control group of individuals with complete permanent dentition were examined. Taurodontism was assessed on permanent mandibular first molars. The difference in the frequency of taurodontism among the studied groups was tested with Fisher's Exact Test. ResultsSeventeen families with nonsyndromic familial tooth agenesis were studied. The frequency of taurodontism was 29% in patients with tooth agenesis, 10.3% in their first and second degree relatives, and 6.6% in the control group. A significant statistical difference among the studied groups was observed (p=0.002). Taurodontism was proportionally more frequent in patients with a higher number of absent teeth. It was mainly observed in patients from families in which the proband was diagnosed with oligodontia. ConclusionsTaurodontism is more frequent in nonsyndromic familial tooth agenesis. Individuals in families with second premolar and molar oligodontia are more likely to have taurodontism, even the individuals with complete dentition. This association could define a subphenotype for future genetic studies of dental development.

Developmental biology and genetics of dental malformations

The synthesis of tooth development biology with human studies focusing on inherited conditions that specifically interfere with tooth development is improving our understanding of normal and pathological tooth formation. The type of inherited dental malformations observed in a given kindred relate to when, during odontogenesis, the defective gene is critically expressed. Information about the protein encoded by the defective gene and the resulting dental phenotype helps us understand the major processes underway at different stages during tooth development. Genes affecting early tooth development (PAX9, MSX1, and AXIN2) are associated with familial tooth agenesis or oligodontia. Genes expressed by odontoblasts (COL1A1, COL1A2, and DSPP), and ameloblasts (AMELX, ENAM, MMP20, and KLK4) during the crown formation stage, are associated with dentinogenesis imperfecta, dentin dysplasia, and amelogenesis imperfecta. Late genes expressed during root formation (ALPL and DLX3) are associated with cementum agenesis (hypophosphatasia) and taurodontism. Understanding the relationships between normal tooth development and the dental pathologies associated with inherited diseases improves our ability to diagnose and treat patients suffering the manifestations of inherited dental disorders.

Mutations in AXIN2 Cause Familial Tooth Agenesis and Predispose to Colorectal Cancer

Wnt signaling regulates embryonic pattern formation and morphogenesis of most organs. Aberrations of regulation of Wnt signaling may lead to cancer. Here, we have used positional cloning to identify the causative mutation in a Finnish family in which severe permanent tooth agenesis (oligodontia) and colorectal neoplasia segregate with dominant inheritance. Eleven members of the family lacked at least eight permanent teeth, two of whom developed only three permanent teeth. Colorectal cancer or precancerous lesions of variable types were found in eight of the patients with oligodontia. We show that oligodontia and predisposition to cancer are caused by a nonsense mutation, Arg656Stop, in the Wnt-signaling regulator AXIN2. In addition, we identified a de novo frameshift mutation 1994-1995insG in AXIN2 in an unrelated young patient with severe tooth agenesis. Both mutations are expected to activate Wnt signaling. The results provide the first evidence of the importance of Wnt signaling for the development of dentition in humans and suggest that an intricate control of Wnt-signal activity is necessary for normal tooth development, since both inhibition and stimulation of Wnt signaling may lead to tooth agenesis. Our findings introduce a new gene for hereditary colorectal cancer and suggest that tooth agenesis may be an indicator of cancer susceptibility.

Functional Analysis of a Mutation in PAX9 Associated with Familial Tooth Agenesis in Humans

Pax9 is a paired domain-containing transcription factor that plays an essential role in the patterning of murine dentition. In humans, mutations in PAX9 are associated with unique phenotypes of familial tooth agenesis that mainly involve posterior teeth. Among these, a frameshift mutation (219InsG) within the paired domain of PAX9 produces a protein product associated with a severe form of molar agenesis in a single family. The objectives of this study were to gain new insights into the molecular pathogenesis of the 219InsG mutation and its role in tooth agenesis. Here we describe functional defects in DNA binding and transactivation of mutant 219InsGPax9. Although wild type Pax9 binds to the high affinity paired domain recognition sequences, e5 and CD19-2(A-ins), the 219InsGPax9 mutant protein was unable to bind to these cognate DNA-binding sites. In co-transfection assays, wild type Pax9 activated reporter gene transcription although the mutant was transcriptionally inactive. Immunolocalization data show that Pax9 and 219InsGPax9 proteins are synthesized in mammalian cells but that the nuclear localization of the mutant Pax9 protein is altered. Furthermore, transactivation by the full-length Pax9 protein from paired domain binding sites was not impaired by the 219InsGPax9 mutant. The latter did not alter the DNA binding activities of wild type Pax9 in gel mobility shift assays. The combined defects in DNA binding activities and transactivation function of mutant 219InsGPAX9 likely alter the selective activation and/or repression of PAX9 effector genes during odontogenesis. This loss-of-function of PAX9 most likely results in its haploinsufficiency during the patterning of dentition and the subsequent loss of posterior teeth.

Clinical, radiographic, and genetic evaluation of a novel form of autosomal-dominant oligodontia.

A frameshift mutation recently identified within the paired domain of the transcription factor, PAX9, has been linked to a unique form of oligodontia in a single, multigenerational family (Stockton et al., 2000). We now describe the phenotypic and segregation analyses of this remarkable kindred, the initial approach taken to identify a candidate gene involved in this form of oligodontia, and the power of this single-family pedigree to generate significant linkage in a genome search. Of the 43 family members enrolled in this study, 21 individuals were affected with several congenitally missing permanent teeth. The pattern of inheritance of the oligodontia trait suggested the involvement of a single gene bearing a dominant mutation. To various degrees, affected members lacked permanent first, second, and third molars in all four quadrants. Several individuals with missing molars also lacked second premolars- most commonly, maxillary second premolars and mandibular central incisors. To the best of our knowledge, this pattern of non-syndromic, familial tooth agenesis has not been previously described in the literature. Since a missense mutation in the homeobox gene, MSX1, was previously linked to tooth agenesis in a single family lacking second premolars and third molars, we performed a mutational analysis of MSX1 by PCR. The absence of a mutation in exons 1 and 2 of MSX1 suggested that allelic mutations in the coding region of MSX1 are not associated with this phenotypically distinct form of oligodontia. Computer simulation of linkage analysis further proved that this pedigree alone was sufficient to generate a significant result for a total genome scan.

A human MSX1 homeodomain missense mutation causes selective tooth agenesis

We demonstrate that a mutation in the homeobox gene, MSX1, causes a common developmental anomaly, familial tooth agenesis. Genetic linkage analyses in a family with autosomal dominant agenesis of second premolars and third molars identified a locus on chromosome 4p, where the MSX1 gene resides. Sequence analyses demonstrated an Arg31Pro missense mutation in the homeodomain of MSX1 in all affected family members. Arg 31 is a highly conserved homeodomain residue that interacts with the ribose phosphate backbone of target DNA. We propose that the Arg31 Pro mutatrion comprises MSX1 interactions, and suggest that MSX1 functions are critical for normal development of specific human teeth.