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

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>T (p.Gly51Val), c.239delC (p.Thr82Profs*3), and c.409C>T (q.Gln137Ter). In addition, two previously reported missense variants were identified: c.140G>C (p.Arg47Pro) and c.146C>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>C, p.R47P, and c.152G>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.

Genome-wide screening for deubiquitinase subfamily identifies ubiquitin-specific protease 49 as a novel regulator of odontogenesis

Proteins expressed by the paired box gene 9 (PAX9) and Msh Homeobox 1 (MSX1) are intimately involved in tooth development (odontogenesis). The regulation of PAX9 and MSX1 protein turnover by deubiquitinating enzymes (DUBs) plausibly maintain the required levels of PAX9 and MSX1 during odontogenesis. Herein, we used a loss-of-function CRISPR-Cas9-mediated DUB KO library kit to screen for DUBs that regulate PAX9 and MSX1 protein levels. We identify and demonstrate that USP49 interacts with and deubiquitinates PAX9 and MSX1, thereby extending their protein half-lives. On the other hand, the loss of USP49 reduces the levels of PAX9 and MSX1 proteins, which causes transient retardation of odontogenic differentiation in human dental pulp stem cells and delays the differentiation of human pluripotent stem cells into the neural crest cell lineage. USP49 depletion produced several morphological defects during tooth development, such as reduced dentin growth with shrunken enamel space, and abnormal enamel formation including irregular mineralization. In sum, our results suggest that deubiquitination of PAX9 and MSX1 by USP49 stabilizes their protein levels to facilitate successful odontogenesis.

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.

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.

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.

TGFβ3, MSX1, and MMP3 as Candidates for NSCL±P in an Indian Population

OBJECTIVE

To evaluate the association of transforming growth factor β3 ( TGFβ3), muscle segment homeobox 1 ( MSX1), Metalloproteinases 3 ( MMP3), and MMP9 genes as candidates for nonsyndromic cleft lip and/or palate in an Indian population.

DESIGN

Case-control association study, mutational screening, and functional evaluation of obtained mutations.

SETTING

Mutational screening of the developmental genes, TGFβ3 and MSX1, along with functional evaluation and association of promoter region SNPs-one each in MMP3 and MMP9.

PATIENTS, PARTICIPANTS

Two hundred forty five NSCL±P cases from G. S. Memorial Plastic Surgery Hospital and Trauma Center, Varanasi and 201 healthy controls without a family history of congenital malformations from nearby schools, primary health centers, and the university hospital.

MAIN OUTCOME MEASURE(S)

Sequencing, SSCP, and PCR-RFLP were used for candidate gene screening. MatInspector and electrophoretic mobility shift assay (EMSA) were used to check the differential transcription factor binding of the variants at promoter region. Luciferase assay was used to test the transcriptional potential of the variant, and evaluation of the alternative splice site was carried out using exon-trapping experiment.

RESULTS

Metalloproteinases3 -1171 5A/6A was associated with NSCL±P, whereas MMP9 -1562 C/T did not show association. A rare variant in the promoter region of TGFβ3 (rs117462711) creates a differential binding site, confirmed by EMSA. Luciferase assay showed 3.7-fold increased expression level in mutant construct. A synonymous change in MSX1 (rs34165410) showed association with NSCL±P, which may create an alternative splice site or lead to low codon usage. Exon-trapping experiment failed to confirm alternative splicing, indicating low codon usage frequency of the mutant affecting the gene function.

CONCLUSIONS

TGFβ3, MSX1, and MMP3 are candidates for NSCL±P.

A review on non-syndromic tooth agenesis associated with PAX9 mutations

Tooth agenesis in the reduction of tooth number which includes hypodontia, oligodontia and anodontia is caused by disturbances and gene mutations that occur during odontogenesis. To date, several genetic mutations that unlock the causes of non-syndromic tooth agenesis are being discovered; these have been associated with certain illnesses because tooth development involves the interaction of several genes for tooth epithelium and mesenchyme odontogenesis. Mutation of candidate genes PAX9 and MSX1 have been identified as the main causes of hypodontia and oligodontia; meanwhile, AXIN2 mutation is associated with anodontia. Previous study using animal models reported that PAX9-deficient knockout mice exhibit missing molars due to an arrest of tooth development at the bud stage. PAX9 frameshift, missense and nonsense mutations are reported to be responsible; however, the most severe condition showed by the phenotype is caused by haploinsufficiency. This suggests that PAX9 is dosage-sensitive. Understanding the mechanism of genetic mutations will benefit clinicians and human geneticists in future alternative treatment investigations.

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.

Possible association between acetazolamide administration during pregnancy and multiple congenital malformations

Congenital malformations might occur because of environmental or genetic factors, and sometimes occur because of unknown causes. Acetazolamide is a carbonic anhydrase inhibitor that is used to treat idiopathic intracranial hypertension, glaucoma, and epilepsy. The use of acetazolamide has not been recommended for pregnant women because of reported teratogenic risks. Congenital malformations, such as ectrodactyly, syndactyly, cleft lip/palate, and retarded incisor teeth development, have been reported in experimental animals. However, tooth agenesis due to the use of acetazolamide has not been reported yet. Oligodontia is a severe type of tooth agenesis involving six or more congenitally missing teeth. The causes of oligodontia are attributed to environmental factors, such as irradiation, drugs, trauma, tumors, infection, genetic factors, or a combination. There is no credible evidence of undesirable effects of acetazolamide use in human pregnancy. However, we report a case of a 12-year-old Saudi boy who was exposed to maternal acetazolamide (1,000 mg/day) for treatment of idiopathic intracranial hypertension before pregnancy, during the first trimester, and throughout the pregnancy. This treatment might have resulted in some congenital malformations, such as ectrodactyly, syndactyly, and oligodontia.

DNA methylation is critical for tooth agenesis: implications for sporadic non-syndromic anodontia and hypodontia

Hypodontia is caused by interactions among genetic, epigenetic, and environmental factors during tooth development, but the actual mechanism is unknown. DNA methylation now appears to play a significant role in abnormal developments, flawed phenotypes, and acquired diseases. Methylated DNA immunoprecipitation (MeDIP) has been developed as a new method of scanning large-scale DNA-methylation profiles within particular regions or in the entire genome. Here, we performed a genome-wide scan of paired DNA samples obtained from 4 patients lacking two mandibular incisors and 4 healthy controls with normal dentition. We scanned another female with non-syndromic anodontia and her younger brother with the same gene mutations of the PAX9,MSX1,AXIN2 and EDA, but without developmental abnormalities in the dentition. Results showed significant differences in the methylation level of the whole genome between the hypodontia and the normal groups. Nine genes were spotted, some of which have not been associated with dental development; these genes were related mainly to the development of cartilage, bone, teeth, and neural transduction, which implied a potential gene cascade network in hypodontia at the methylation level. This pilot study reveals the critical role of DNA methylation in hypodontia and might provide insights into developmental biology and the pathobiology of acquired diseases.

Hypodontia and ovarian cancer: A systematic review

Hypodontia can be defined as the non-formation of one or more teeth during the developmental period. Mutation in several genes related to tooth formation has previously been correlated with cancer. Regarding the ovarian cancer, there are few studies that associate the presence of hypodontia with ovarian cancer. A systematic literature search was performed in PubMed and Scopus. In total, 385 patients were included in this study. Control group was present in 3 out of 4 studies (340 patients). Hypodontia was present in 56 out of 290 patients (incidence of 19.3%). Only in 2 out of 4 studies, the number of missing teeth was mentioned (47 teeth), while the majority of them were either maxillary second premolars or maxillary lateral incisors. Unilateral distribution of the missing teeth was present in 28 out of 46 patients, while bilateral distribution of the missing teeth was present in 18 out of 46 patients. The presence of ovarian cancer in the family medical history occurred in 12 out of 33 patients. Only 1 out of 4 studies examined the presence of genes with mutations in the included patients. Based on our findings, the lack of clinical studies was the principal obstacle to clarify the possible predictive value of hypodontia in the early prediction of patients with higher risk of ovarian cancer.

An aberrant splice acceptor site due to a novel intronic nucleotide substitution in MSX1 gene is the cause of congenital tooth agenesis in a Japanese family

Congenital tooth agenesis is caused by mutations in the MSX1, PAX9, WNT10A, or AXIN2 genes. Here, we report a Japanese family with nonsyndromic tooth agenesis caused by a novel nucleotide substitution in the intronic region between exons 1 and 2 of the MSX1 gene. Because the mutation is located 9 bp before exon 2 (c.452-9G>A), we speculated that the nucleotide substitution would generate an abnormal splice site. Using cDNA analysis of an immortalized patient blood cell, we confirmed that an additional 7-nucleotide sequence was inserted at the splice junction between exons 1 and 2 (c.451_452insCCCTCAG). The consequent frameshift generated a homeodomain-truncated MSX1 (p.R151fsX20). We then studied the subcellular localization of truncated MSX1 protein in COS cells, and observed that it had a whole cell distribution more than a nuclear localization, compared to that of wild-type protein. This result suggests a deletion of the nuclear localization signal, which is mapped to the MSX1 homeodomain. These results indicate that this novel intronic nucleotide substitution is the cause of tooth agenesis in this family. To date, most MSX1 variants isolated from patients with tooth agenesis involve single amino acid substitutions in the highly conserved homeodomain or deletion mutants caused by frameshift or nonsense mutations. We here report a rare case of an intronic mutation of the MSX1 gene responsible for human tooth agenesis. In addition, the missing tooth patterns were slightly but significantly different between an affected monozygotic twin pair of this family, showing that epigenetic or environmental factors also affect the phenotypic variations of missing teeth among patients with nonsyndromic tooth agenesis caused by an MSX1 haploinsufficiency.

Mutations in the MSX1 gene in Turkish children with non-syndromic tooth agenesis and other dental anomalies

Aim:

To search for mutations on the MSX1 gene and to present a genetic basis for non-syndromic tooth agenesis in conjunction with dental anomalies in a Turkish population.

Materials and Methods:

The patients included in this study were otherwise healthy, with ages ranging from seven to eighteen years. Eighty-two of them had one to six teeth missing (Group I) and 26 had more than six teeth missing (Group II), except for the third molars,. The missing teeth and dental anomalies were examined clinically and radiographically. The MSX1 gene was sequenced from the blood samples of patients who consented to the study.

Results:

Mutations or polymorphisms on the MSX1 gene were identified in six patients. Taurodontism was seen in patients from both groups I and II. The nucleotide changes were identified by mutation screening.

Conclusions:

Performing family studies, screening other candidate genes, and investigation of interactions between genes will provide a basis for better analysis of tooth agenesis models and their association with other dental anomalies.

Axis inhibition protein 2 polymorphisms may be a risk factor for families with isolated oligodontia

The objective of the present study was to search for Msh homeobox 1 (MSX1), paired box gene 9 (PAX9), ectodysplasin‑A (EDA) and axis inhibition protein 2 (AXIN2) variants in a family with isolated oligodontia and analyse the pathogenesis of mutations that result in oligodontia phenotypes. Members of a single family (but of different descent) with oligodontia and unrelated healthy controls were enrolled in our study. Genomic DNA was isolated from blood samples. Mutation analysis was performed by amplifying MSX1, PAX9, EDA and AXIN2 exons as well as their exon‑intron boundaries and sequencing the products. DNA sequencing of the AXIN2 gene revealed three mutations in the two patients with oligodontia: a homozygotic silent mutation c.1365A>G (p.Pro455=) in exon 3, two c.956+16A>G mutations (II‑1: homozygosis; III‑1: heterozygosis) and c.1200+71A>G (homozygosis) in the intron, which possibly contributed to structural and functional changes in proteins. The heterozygotic mutations c.1365A>G and c.1200+71A>G were identified in the proband's mother (II‑2). No mutations were detected in the MSX1, PAX9 and EDA genes of oligodontia patients. The findings suggest that the c.956+16A>G, c.1365A>G and c.1200+71A>G mutations of AXIN2 may be responsible for the oligodontia phenotype in this family, but these findings require further study.

Whole genome sequencing reveals novel non-synonymous mutation in ectodysplasin A (EDA) associated with non-syndromic X-linked dominant congenital tooth agenesis

Congenital tooth agenesis in human is characterized by failure of tooth development during tooth organogenesis. 300 genes in mouse and 30 genes in human so far have been known to regulate tooth development. However, candidature of only 5 genes viz. PAX9, MSX1, AXIN2, WNT10A and EDA have been experimentally established for congenitally missing teeth like hypodontia and oligodontia. In this study an Indian family with multiple congenital tooth agenesis was identified. Pattern of inheritance was apparently autosomal dominant type with a rare possibility to be X-linked. Whole genome sequencing of two affected individuals was carried out which revealed 119 novel non-synonymous single nucleotide variations (SNVs) distributed among 117 genes. Out of these only one variation (c.956G>T) located at exon 9 of X-linked EDA gene was considered as pathogenic and validated among all the affected and unaffected family members and unrelated controls. This variation leads to p.Ser319Ile change in the TNF homology domain of EDA (transcript variant 1) protein. In silico analysis predicts that this Ser319 is well conserved across different vertebrate species and a part of putative receptor binding site. Structure based homology modeling predicts that this amino acid residue along with four other amino acid residues nearby, those when mutated known to cause selective tooth agenesis, form a cluster that may have functional significance. Taken together these results suggest that c.956G>T (p.Ser319Ile) mutation plausibly reduces the receptor binding activity of EDA leading to distinct tooth agenesis in this family.

PAX genes in childhood oncogenesis: developmental biology gone awry?

Childhood solid tumors often arise from embryonal-like cells, which are distinct from the epithelial cancers observed in adults, and etiologically can be considered as 'developmental patterning gone awry'. Paired-box (PAX) genes encode a family of evolutionarily conserved transcription factors that are important regulators of cell lineage specification, migration and tissue patterning. PAX loss-of-function mutations are well known to cause potent developmental phenotypes in animal models and underlie genetic disease in humans, whereas dysregulation and/or genetic modification of PAX genes have been shown to function as critical triggers for human tumorigenesis. Consequently, exploring PAX-related pathobiology generates insights into both normal developmental biology and key molecular mechanisms that underlie pediatric cancer, which are the topics of this review.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Identification of Genetic Risk Factors for Maxillary Lateral Incisor Agenesis

Tooth agenesis affects 20% of the world population, and maxillary lateral incisors agenesis (MLIA) is one of the most frequent subtypes, characterized by the absence of formation of deciduous or permanent lateral incisors. Odontogenesis is a complex mechanism regulated by sequential and reciprocal epithelial-mesenchymal interactions, controlled by activators and inhibitors involved in several pathways. Disturbances in these signaling cascades can lead to abnormalities in odontogenesis, resulting in alterations in the formation of the normal teeth number. Our aim was to study a large number of genes encoding either transcription factors or key components in signaling pathways shown to be involved in tooth odontogenesis. We selected 8 genes— MSX1, PAX9, AXIN2, EDA, SPRY2, TGFA, SPRY4, and WNT10A—and performed one of the largest case-control studies taking into account the number of genes and variants assessed, aiming at the identification of MLIA susceptibility factors. We show the involvement of PAX9, EDA, SPRY2, SPRY4, and WNT10A as risk factors for MLIA. Additionally, we uncovered 3 strong synergistic interactions between MLIA liability and MSX1- TGFA, AXIN2- TGFA, and SPRY2- SPRY4 gene pairs. We report the first evidence of the involvement of sprouty genes in MLIA susceptibility. This large study results in a better understanding of the genetic components and mechanisms underlying this trait.

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.

Mutational analysis of AXIN2, MSX1, and PAX9 in two Mexican oligodontia families

The genes for axin inhibition protein 2 (AXIN2), msh homeobox 1 (MSX1), and paired box gene 9 (PAX9) are involved in tooth root formation and tooth development. Mutations of the AXIN2, MSX1, and PAX9 genes are associated with non-syndromic oligodontia. In this study, we investigated phenotype and AXIN2, MSX1, and PAX9 gene variations in two Mexican families with non-syndromic oligodontia. Individuals from two families underwent clinical examinations, including an intra-oral examination and panoramic radiograph. Retrospective data were reviewed, and peripheral blood samples were collected. The exons and exon-intronic boundaries of the AXIN2, MSX1, and PAX9 genes were sequenced and analyzed. Protein and messenger RNA structures were predicted using bioinformative software programs. Clinical and oral examinations revealed isolated non-syndromic oligodontia in the two Mexican families. The average number of missing teeth was 12. The sequence analysis of exons and exon-intronic regions of AXIN2, MSX1, and PAX9 revealed 11 single-nucleotide polymorphisms (SNPs), including seven in AXIN2, two in MSX1, and three in PAX9. One novel SNP of MSX1, c.476T>G (Leu159Arg), was found in all of the studied patients in the families. MSX1 Leu159Arg and PAX9 Ala240Pro change protein and messenger RNA structures. Our findings suggested that a combined reduction of MSX1 and PAX9 gene dosages increased the risk for oligodontia in the Mexican families, as in vivo investigation has indicated that interaction between Msx1 and Pax9 is required for tooth development.

Genetic background of nonsyndromic oligodontia: a systematic review and meta-analysis

OBJECTIVES

The goal of this work was to identify all known gene mutations that have been associated with the development of nonsyndromic oligodontia.

METHODS

A systematic literature search was performed electronically in two databases (PubMed, Medpilot) supplemented by a hand search. Articles published up to March 2012 were considered. Search terms were combined as follows: oligodontia and genes, oligodontia and mutations, tooth agenesis and genes, and tooth agenesis and mutations. A meta-analysis of the data was conducted based on the Tooth Agenesis Code (TAC).

RESULTS

Seven genes are currently known to have a potential for causing nonsyndromic oligodontia. All these genes vary both in terms of number of identified mutations and in terms of number of documented patients: 33 mutations and 93 patients are on record for PAX9, 10 mutations and 51 patients for EDA, 12 mutations and 33 patients for MSX1, 6 mutations and 17 patients for AXIN2, and 1 mutation in 1 patient for EDARADD, NEMO, and KRT17 each. A total TAC score of 250 was found to have cutoff properties, as 100% of MSX1 and 80% of EDA patients exhibited TAC ≤ 250, whereas 96.9% of PAX9 and 90% of AXIN2 patients exhibited TAC >250. Furthermore, 94.3% of EDA patients but only 28.6% of MSX1 patients exhibited odd-numbered TAC scores in at least one quadrant, and 72.7% of PAX9 but none of the AXIN2 patients were found to show TAC scores of 112 in at least one quadrant.

CONCLUSION

In order of decreasing frequency, PAX9, EDA, MSX1, AXIN2, EDARADD, NEMO, and KRT17 are the seven genes currently known to have a potential for causing nonsyndromic oligodontia. TAC scores enabled us to identify an association between oligodontia phenotypes and genotypes in the patients covered by this meta-analysis.

Clinical and genetic evaluation of a Chinese family with isolated oligodontia

OBJECTIVES

Oligodontia is defined as the congenital absence of 6 or more permanent teeth excluding the third molar. Tooth agenesis may be classified as syndromic/non-syndromic and as familial/sporadic. To date, more than 300 genes have been found to be involved in tooth development, but only a few of these genes, such as MSX1, PAX9 and AXIN2, are related to the condition of non-syndromic oligodontia. The objective of the present work was to investigate the disease-causing gene of non-syndromic oligodontia in a Han Chinese family and analyse the pathogenesis of mutations that result in oligodontia.

DESIGN

We examined all individuals of the oligodontia family by clinical and radiographic examinations. Based on the clinical manifestations, the candidate genes MSX, PAX9 and AXIN2 were selected to analyse and screen for mutations.

RESULTS

The clinical evaluation suggested that the family might show non-syndromic oligodontia. DNA sequencing of the MSX1 gene revealed two mutations in the two patients with oligodontia: a heterozygotic silent mutation, c.348C>T (P.Gly116=), in exon 1 and a homozygotic deletion of 11 nucleotides (c.469+56delins GCCGGGTGGGG) in the intron. However, the silent mutation and the deletion mutation were thought to be known polymorphisms (rs34165410 and rs34341187) by bioinformatics analysis. We did not detect any mutations in the PAX9 and AXIN2 genes of oligodontia patients.

CONCLUSION

Our finding suggests that identified polymorphisms (c.348C>T and c.469+56delins GCCGGGTGGGG) may be responsible for the oligodontia phenotype in this Chinese family, but the association requires further study.

Tooth agenesis patterns and phenotype variation in a cohort of Belgian patients with hypodontia and oligodontia clustered in 79 families with their pedigrees

BACKGROUND

Even though tooth agenesis is the most common developmental anomaly of the human dentition, its genetic background and pathogenic mechanism(s) still remain poorly understood. Syndromic and isolated forms of hypodontia have been described and can occur sporadically or in families.

OBJECTIVES

We describe and analyse the hypo-/oligodontia phenotype variations in families. The index patient suffers from severe or mild hypodontia; case-parents/sib records are available. Furthermore, we aim to evaluate whether the different agenesis patterns in the pedigrees are predictive of mutations in specific genes based on reported genotype-phenotype associations.

MATERIALS AND METHODS

Dental records and pedigrees were collected from 79 families. In 67 families, the index patient presented with oligodontia while in 12 families with hypodontia. The phenotype data of 66 oligodontia index patients were analysed with the Tooth Agenesis Code software.

RESULTS

Nine families counted two members; one family counted three members affected with oligodontia. Twenty-four oligodontia families respectively had one (n = 17), two (n = 4), three (n = 2) or four (n = 1) additional family members presenting with hypodontia. Of the 77 oligodontia cases, two showed the same tooth agenesis pattern, while 75 patients showed unique tooth agenesis patterns.

CONCLUSIONS

Despite familial aggregation and expected Mendelian segregation, the number of missing teeth in the familial hypo-/oligodontia phenotypes and the tooth agenesis patterns are highly variable between the affected family members. Therefore, we hypothesize that tooth agenesis is not (always) a simple monogenic condition, but additional genetic or environmental factors can modify the expression of the phenotype.