Novel nonsense mutation in MSX1 in familial nonsyndromic oligodontia: subcellular localization and role of homeodomain/MH4

Nonsyndromic tooth agenesis is one of the most common anomalies in human development. Part of the malformation is inherited and is associated with paired box 9 (PAX9), msh homeobox 1 (MSX1), and axin 2 (AXIN2) mutations. To obtain a comprehensive understanding of the genetic and molecular mechanisms that underlie this genetic disease, we investigated six familial and seven sporadic Japanese cases of nonsyndromic tooth agenesis. Searches for mutations in these candidate genes detected a novel nonsense mutation (c.416G>A) in exon 1 of MSX1 from a family with oligodontia. This mutation co‐segregated in the affected family members. Moreover, this mutation produced a termination codon in the first exon and therefore the gene product (W139X) was truncated at the C terminus, hence, the entire homeodomain/MH4, which has many functions, such as DNA binding, protein‐protein interaction, and nuclear localization, was absent. We characterized the properties of this truncated MSX1 by investigating the subcellular localization of the mutant gene product in transfected cells. The wild‐type MSX1 localized exclusively at the nuclear periphery of transfected cells, whereas the mutant MSX1 was stable but localized diffusely throughout the whole cell. These results indicate that W139X MSX1 is responsible for tooth agenesis.     

MSX1, PAX9, and TGFA contribute to tooth agenesis in humans

In this study, we sought to determine the association between tooth agenesis and DNA sequence variation in the genes MSX1 and PAX9 in an ethnically diverse human population. Since cleft lip/palate is also associated with both tooth agenesis and the gene TGFA, we included TGFA in the analysis as well. Cheek swab samples were obtained for DNA analysis from 116 case/parent trios. Probands had at least one developmentally missing tooth, excluding third molars. Genotyping was performed by single-strand conformational polymorphism or kinetic polymerase chain-reaction assays. Transmission distortion of the marker alleles and DNA sequence analysis was performed. Results showed that tooth agenesis is associated with markers of the genes MSX1 and TGFA. No mutations were found in MSX1 or PAX9 coding regions. There were statistically significant data suggesting that MSX1 interacts with PAX9. These findings suggest that MSX1, PAX9, and TGFA play a role in isolated dental agenesis.     

A screen of a large Czech cohort of oligodontia patients implicates a novel mutation in the PAX9 gene

Tooth agenesis is one of the most common developmental anomalies in humans. To date, many mutations involving paired box 9 (PAX9), msh homeobox 1 (MSX1), and axin 2 (AXIN2) genes have been identified. The aim of the present study was to perform screening for mutations and/or polymorphisms using the capillary sequencing method in the critical regions of PAX9 and MSX1 genes in a group of 270 individuals with tooth agenesis and in 30 healthy subjects of Czech origin. This screening revealed a previously unknown heterozygous g.9527G>T mutation in the PAX9 gene in monozygotic twins with oligodontia and three additional affected family members. The same variant was not found in healthy relatives. This mutation is located in intron 2, in the region recognized as the splice site between exon 2 and intron 2. We hypothesize that the error in pre‐mRNA splicing may lead to lower expression of PAX9 protein and could have contributed to the development of tooth agenesis in the affected subjects.     

Novel mutation in the paired box sequence of PAX9 gene in a sporadic form of oligodontia

Tooth development is regulated through a series of reciprocal interactions between the dental epithelium and mesenchyme and requires protein products of a number of genes. It has been reported that selective tooth agenesis is associated with mutations in human MSX and PAX9 genes. Mutational analysis of the two genes was performed in 25 individuals with familial or sporadic form of permanent tooth agenesis. Single-stranded conformational polymorphism analysis revealed no mutations in the entire coding sequence of the MSX1 gene. In PAX9, a novel, heterozygous G151A transition in the sequence encoding the paired domain of the PAX9 protein was detected in a patient with agenesis of third molars, second premolars and incisors, but not in her parents, the remaining patients or 162 individuals with normal dentition. This is the first de novo mutation described in PAX9. Our results support the view that mutations in PAX9 could constitute a causative factor of oligodontia. We hypothesize that the G151A transition in PAX9 might be responsible for the sporadic form of tooth agenesis in this patient.     

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

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

A novel WNT10A mutation causes non-syndromic hypodontia in an Egyptian family

Objective

Tooth agenesis is the most common dental anomaly, whose aetiology still remains to be fully elucidated. The aim of this study was to investigate the genetic cause of non-syndromic hypodontia with clinical variability in an Egyptian family.

Design

The entire coding regions including exon-intron boundaries of the MSX1, PAX9 and WNT10A genes were investigated by direct sequencing in all affected family members.

Results

Novel heterozygous mutation inherited in an autosomal dominant manner was identified in the WNT10A gene. This 21-bp deletion combined with 1-bp insertion, c.-14_7delinsC, eliminates the translation initiation codon leading to either no protein production or translation of alternative open reading frames. None of the control subjects (400 chromosomes) were carriers of this novel WNT10A mutation. No pathogenic mutations were found in the MSX1 and PAX9 genes.

Conclusions

The novel c.-14_7delinsC mutation might be the etiological variant of the WNT10A gene responsible for the permanent tooth agenesis in the Egyptian family. WNT10A is a major candidate gene for non-syndromic hypodontia.     

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

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

Material and Methods:

The female proband and her family members from the ethnic Han families underwent complete oral examinations and received a retrospective review. Venous blood samples were obtained to screen variants in the PAX9, MSX1, AXIN2, and EDA genes. A case-control study was performed on 50 subjects with sporadic tooth agenesis (cases) and 100 healthy controls, which genotyped a PAX9 gene polymorphism (rs4904210).

Results:

Intra-oral and panoramic radiographs revealed that the female proband had anodontia denoted by the complete absence of teeth in both the primary and secondary dentitions, while all her family members maintained normal dentitions. Detected in the female proband were variants of the PAX9 and AXIN2 including A240P (rs4904210) of the PAX9, c.148C>T (rs2240308), c.1365A>G (rs9915936) and c.1386C>T (rs1133683) of the AXIN2. The same variants were present in her unaffected younger brother. The PAX9 variations were in a different state in her parents. Mutations in the MSX1 and EDA genes were not identified. No significant diferences were found in the allele and genotype frequencies of the PAX9 polymorphism between the controls and the subjects with sporadic tooth agenesis.

Conclusions:

These results suggest that the association of A240P with sporadic tooth agenesis still remains obscure, especially for different populations. The genotype/phenotype correlation in congenital anodontia should be verified.     

MSX1 and orofacial clefting with and without tooth agenesis

MSX1 has been considered a strong candidate for orofacial clefting, based on mouse expression studies and knockout models, as well as association and linkage studies in humans. MSX1 mutations are also causal for hereditary tooth agenesis. We tested the hypothesis that individuals with orofacial clefting with or without tooth agenesis have MSX1 coding mutations by screening 33 individuals with cleft lip with or without cleft palate (CL/P) and 19 individuals with both orofacial clefting and tooth agenesis. Although no MSX1 coding mutations were identified, the known 101C > G variant occurred more often in subjects with both CL/P and tooth agenesis (p = 0.0008), while the *6C-T variant was found more often in CL/P subjects (p = 0.001). Coding mutations in MSX1 are not the cause of orofacial clefting with or without tooth agenesis in this study population. However, the significant association of MSX1 with both phenotypes implies that MSX1 regulatory elements may be mutated.     

Novel MSX1 mutation in a family with autosomal-dominant hypodontia of second premolars and third molars

ObjectiveTooth agenesis is the most common developmental anomaly of the human dentition, with aetiology involving both genetic and environmental factors. The aim of the study was to search for casual mutations underlying hypodontia in a family with agenesis of the second premolars and third molars.DesignDirect sequencing of the coding regions including exon–intron boundaries of the MSX1 and PAX9 genes was performed in all affected family members.ResultsNovel heterozygous mutation segregating in an autosomal dominant model was identified in the MSX1 gene. This c.T671C transition leads to a substitution of leucine by proline at position 224, which is the penultimate amino acid residue of the highly conserved homeodomain. None of the control subjects (600 chromosomes) were carriers of this novel, probably damaging to protein function, mutation.ConclusionsOur results demonstrate for the first time that MSX1 might play a substantial role in familial cases of hypodontia involving only second premolars and third molars. The novel c.T671C mutation might be the etiological variant of the MSX1 gene responsible for the lack of permanent teeth in the tested family.     

Novel mutation of the initiation codon of PAX9 causes oligodontia

Tooth development is under strict genetic control. Oligodontia is defined as the congenital absence of 6 or more permanent teeth, excluding the third molar. The occurrence of non-syndromic oligodontia is poorly understood, but in recent years several cases have been described where a single gene mutation is associated with oligodontia. Several studies have shown that MSX1 and PAX9 play a role in early tooth development. We screened one family with non-syndromic oligodontia for mutations in MSX1 and PAX9. The pedigree showed an autosomal-dominant pattern of inheritance. Direct sequencing and restriction enzyme analysis revealed a novel heterozygous A to G transition mutation in the AUG initiation codon of PAX9 in exon 1 in the affected members of the family. This is the first mutation found in the initiation codon of PAX9, and we suggest that it causes haploinsufficiency.     

Novel MSX1 frameshift causes autosomal-dominant oligodontia

Can kindreds with tooth agenesis caused by MSX1 or PAX9 mutations be distinguished by their phenotypes? We have identified an MSX1second bicuspids and mandibular central incisors. The dominant phenotype is apparently due to haploinsufficiency. We analyzed patterns of partial tooth agenesis in seven kindreds with defined MSX1 mutations and ten kindreds with defined PAX9 mutations. The probability of missing a particular type of tooth is always bilaterally symmetrical, but differences exist between the maxilla and mandible. MSX1-associated oligodontia typically includes missing maxillary and mandibular second bicuspids and maxillary first bicuspids. The most distinguishing feature of MSX1-associated oligodontia is the frequent (75%) absence of maxillary first bicuspids, while the most distinguishing feature of PAX9-associated oligodontia is the frequent (> 80%) absence of the maxillary and mandibular second molars.     

A novel PAX9 mutation causing oligodontia

IntroductionAn extended family presenting with several members affected by developmentally missing teeth was investigated by analysis of the MSX1 and PAX9 genes.Materials and methodsSaliva samples were collected and DNA extracted. Primers were designed to span the exons and intron-exon junctions of the MSX1 and PAX9 genes. These primers were optimised using gradient Polymerase Chain Reaction. The amplified fragments were sent for Sanger sequencingResultsa novel heterozygote missense mutation in exon 3 of PAX9 (c.296G > C, p.A99P), was found in two severely affected members of the family as well as a potentially pathogenic heterozygote variant (c.119C > G, p.A40G) in exon 1 of the MSX1 gene.ConclusionThe PAX9 A99P mutation is in the DNA binding domain and is predicted to be pathogenic.