Barbara Biedziak

Axis inhibition protein 2 (AXIN2) polymorphisms may be a risk factor for selective tooth agenesis

AbstractSelective tooth agenesis is the most common developmental abnormality of the human dentition. To date, this abnormality has been associated only with mutations in MSX1 and PAX9 mutations, however it has recently been suggested that mutations of axis inhibition protein 2 (AXIN2) may also contribute to this complex anomaly. The protein product of this gene is a negative regulator of the Wnt-signaling pathway. We searched for AXIN2 variants in a group of patients with tooth agenesis who did not have mutations of MSX1 and PAX9. Using multi-temperature single-stranded conformational polymorphism and sequencing analysis, we identified three novel AXIN2 gene variants: c.956+16A>G, c.1060-17C>T and c.2062C>T. We also observed that individuals carrying the c.956+16G and c.2062T alleles exhibited an increased risk of tooth agenesis. The calculated odds ratio was 2.94 (95% CI 1.104-7.816; p=0.026; pcorr=0.234) and 4.01 (95% CI 1.563-10.301; p=0.002; pcorr=0.018), respectively. Moreover, we found that the c.2062C>T transition may change exon splice enhancer-specific binding sites of the protein splicing regulators SC35 and SF2/ASF. This alternation may negatively affect the splicing process and cellular concentration of AXIN2 protein. Our findings suggest that AXIN2 polymorphic variants may be associated with both hypodontia and oligodontia.

Association between genetic variants of reported candidate genes or regions and risk of cleft lip with or without cleft palate in the polish population

BACKGROUND Cleft lip with or without cleft palate (CL/P) is one of the most common craniofacial malformations, with a complex and multifactorial etiology. Because of the genetic heterogeneity of facial clefts, the aim of this study was to investigate the contribution of previously reported candidate genes and chromosomal loci to the risk of CL/P in the Polish population. METHODS We performed an analysis of 18 polymorphisms of FOXE1, IRF6, MSX1, PAX9, TBX10, FGF10, FGFR1, TGFalpha, TGFbeta3, SUMO1, and the chromosomal region 8q24 in a group of 175 patients with CL/P and a properly matched control group. RESULTS Highly significant results were observed for the IRF6 rs642961 variant and the 8q24 regions rs987525 (odds ratio [OR](AG+AAvsGG), 1.635; 95% confidence interval [CI], 1.153-2.319; p = 0.005; and OR(AC+AAvsCC), 1.962; 95% CI, 1.382-2.785; p = 1.4 x 10(-4), respectively). For rs987525, the results were also significant after correction for multiple comparisons. Borderline association with an increased risk of CL/P was also identified for the SUMO1 locus (rs2350350; OR(CGvsGG), 1.580; 95% CI, 1.056-2.363; p = 0.025). CONCLUSIONS Our findings confirmed that genetic variants of IRF6 and the polymorphism located in the 8q24 gene desert are strongly involved in the etiology of facial clefts in the Polish population sample.

A novel mutation in PAX9 causes familial form of molar oligodontia.

PAX9 is a paired domain transcription factor that plays a critical role in odontogenesis. All mutations of PAX9 identified to date have been associated with nonsyndromic form of tooth agenesis. The present report describes an unusual novel mutation in PAX9 identified in a family with severe molar oligodontia. This heterozygous deletion combined with 24 bp insertion (including a 5′ splice site) is localized in the second exon beyond the highly conserved paired box sequence, and might result either in a premature termination of translation at aa 210 or in an aberrant splicing, leading to a frameshift and premature termination of translation at aa 314. Real-time PCR analysis revealed no mutated transcript in cultured lymphocytes of one of the affected individuals indicating that the novel mutation might result in rapid degradation of the mutated transcript leading to haploinsufficiency of PAX9. Our results support the view that mutations in PAX9 constitute a causative factor in nonsyndromic oligodontia.

A novel c.581C>T transition localized in a highly conserved homeobox sequence ofMSX1: is it responsible for oligodontia?

Even though selective tooth agenesis is the most common developmental anomaly of human dentition, its genetic background still remains poorly understood. To date, familial as well as sporadic forms of both hypodontia and oligodontia have been associated with mutations or polymorphisms ofMSX1, PAX9, AXIN2 andTGFα, whose protein products play a crucial role in odontogenesis. In the present report we described a novel mutation ofMSX1, which might be responsible for the lack of 14 permanent teeth in our proband. However, this c.581C>T transition, localized in a highly conserved homeobox sequence ofMSX1, was identified also in 2 healthy individuals from the proband’s family. Our finding suggests that this transition might be the first described mutation ofMSX1 that might be responsible for oligodontia and showing incomplete penetrance. It may also support the view that this common anomaly of human dentition might be an oligogenic trait caused by simultaneous mutations of different genes.

Nucleotide variants of genes encoding components of the Wnt signalling pathway and the risk of non‐syndromic tooth agenesis

Tooth agenesis is one of the most common dental anomalies, with a complex and not yet fully elucidated aetiology. Given the crucial role of the Wnt signalling pathway during tooth development, the purpose of this study was to determine whether nucleotide variants of genes encoding components of this signalling pathway might be associated with hypodontia and oligodontia in the Polish population. A set of 34 single nucleotide polymorphism (SNPs) in 13 WNT and WNT‐related genes were analyzed in a group of 157 patients with tooth agenesis and a properly matched control group (n = 430). In addition, direct sequencing was performed to detect mutations in the MSX1, PAX9 and WNT10A genes. Both single‐marker and haplotype analyses showed highly significant association between SNPs in the WNT10A gene and the risk for tooth agenesis. Moreover, nine pathogenic mutations within the coding region of the WNT10A gene were identified in 26 out of 42 (62%) tested patients. One novel heterozygous mutation was identified in the PAX9 gene. Borderline association with the risk of non‐syndromic tooth agenesis was also observed for the APC, CTNNB1, DVL2 and WNT11 polymorphisms. In conclusion, nucleotide variants of genes encoding important components of the Wnt signalling pathway might influence the risk of tooth agenesis.

Genotype and haplotype analysis of WNT genes in non-syndromic cleft lip with or without cleft palate

The wingless-type MMTV integration site family (Wnt) signalling pathway plays a crucial role in craniofacial development. Recently, nucleotide variants in WNT genes have been shown to be associated with oral congenital anomalies, including facial clefts. Therefore, in the current study we decided to assay the association of nucleotide variants in selected WNT genes with the risk of non-syndromic cleft lip with or without cleft palate (NCL/P) in the Polish population. Fourteen polymorphisms in WNT3, WNT3A, WNT5A, WNT8A, WNT9B, and WNT11 were tested in a group of 210 patients with NCL/P and in a properly matched control group. The most significant results were found for the WNT3 rs3809857 variant, which, under the assumption of a recessive model, was associated with a two-fold decrease in the risk of NCL/P (OR(TT vs. GT + GG) = 0.492, 95% CI: 0.276-0.879, P = 0.015). Moreover, haplotype analysis revealed that WNT3 is significantly correlated with NCL/P. The global P-values for haplotypes of rs12452064_rs7207916 and rs3809857_rs12452064_rs7207916 were 0.0034 and 0.0014, respectively, and these results were statistically significant, even after the permutation test correction. In conclusion, our study confirmed the involvement of polymorphisms in the WNT3 gene in NCL/P aetiology in the tested population.

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

OBJECTIVE Tooth 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. DESIGN Direct sequencing of the coding regions including exon-intron boundaries of the MSX1 and PAX9 genes was performed in all affected family members. RESULTS Novel 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. CONCLUSIONS Our 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.

Polymorphisms located in the region containing BHMT and BHMT2 genes as maternal protective factors for orofacial clefts.

Nonsyndromic cleft lip with or without cleft palate (NCL/P) is one of the most common craniofacial malformations; however, its aetiology is still unclear. Because the effects of maternal nutrition on fetal development are well known, we decided to pursue the question of whether polymorphic variants of genes encoding enzymes involved in choline metabolism might be associated with the maternal risk of having a baby with NCL/P. Analysis of 18 single nucleotide polymorphisms (SNPs) of betaine-homocysteine methyltransferase (BHMT), betaine-homocysteine methyltransferase-2 (BHMT2), choline dehydrogenase (CHDH), choline kinase (CHKA), dimethylglycine dehydrogenase (DMGDH), choline-phosphate cytidylyltransferase A (PCYT1A), and phosphatidylethanolamine N-methyltransferase (PEMT) provided evidence that polymorphisms located in the region containing BHMT and BHMT2 were protective factors against NCL/P affected pregnancies in our population. The strongest signal was found for the SNP located in the intronic sequence of BHMT2. Women carrying two copies of the rs625879 T allele had a significantly decreased risk of having offspring with orofacial clefts. These results were significant, even after correction for multiple comparisons. Moreover, the gene-gene interaction analysis revealed a significant epistatic interaction of BHMT2 (rs673752), PEMT (rs12325817), and PCYT1A (rs712012) with maternal NCL/P susceptibility. Altogether, our study identified a novel gene, the nucleotide variants of which were be associated with a decreased risk of having a baby with NCL/P.

Polymorphic variants at 10q25.3 and 17q22 loci and the risk of non‐syndromic cleft lip and palate in the polish population

BACKGROUND Non-syndromic cleft lip and palate (CLP) is one of the most common birth defects. Recent genome-wide association studies (GWAS) have identified several novel risk loci associated with this craniofacial anomaly. Therefore, the objective of this report was to investigate the contribution of the top seven polymorphisms reaching genome-wide statistical significance in GWAS analyses in the Polish population. METHODS AND RESULTS Nucleotide variants located at chromosomal regions 1p22.1, 10q25.3, 17q22, and 20q12 were tested in a group of 206 patients with nonsyndromic CLP and a properly matched control group. Significant results, which persisted even after Bonferroni correction (p < 0.0071), were observed for polymorphisms located at 10q25.3 (rs7078160 and rs4752028) and 17q22 (rs227731). Under a recessive model, both rs7078160 and rs4752028 were associated with a greater than fourfold increase in the risk of CLP (odds ratio [OR] = 4.536; 95% confidence interval [CI], 1.678-12.265; p = 0.0012 and OR = 4.573; 95% CI, 1.817-11.512; p = 0.0004, respectively). Polymorphism rs227731 increased the risk of CLP when analyzed under a dominant model (OR = 1.732; 95% CI, 0.184-2.253; p = 0.0044). Borderline association was alsoidentified for the 1p22.1 locus (rs481931). Moreover, 10q25.3 haplotypes were significantly associated with a susceptibility to CLP. CONCLUSION Our evaluation study confirmed a substantial association of polymorphisms located at chromosomal regions 10q25.3 and 17q22 with nonsyndromic CLP in the Polish population.

WNT10A coding variants and maxillary lateral incisor agenesis with associated dental anomalies

Congenital maxillary lateral incisor agenesis (MLIA) is one of the most common subtypes of dental agenesis. Because little is known with regard to the aetiology of this anomaly, the aim of the study was to determine the contribution of nucleotide variants in wingless-type MMTV integration site family, member 10A (WNT10A), msh homeobox 1 (MSX1), and paired box 9 (PAX9) to the risk of MLIA in a Polish population. Coding regions of the selected genes were analysed by direct sequencing in a group of 20 individuals with unilateral and bilateral MLIA, associated or not with other dental anomalies. The frequencies of the identified nucleotide variants were assessed in an additional cohort of patients with isolated dental agenesis (n = 147) and in 178 controls. Mutation screening showed four non-synonymous substitutions located in the highly conserved coding sequence of WNT10A in five (25%) of the 20 patients. Analysis of genotyping results revealed that three of these variants--p.Arg113Cys, p.Phe228Ile, and the newly identified p.Arg171Leu--may represent aetiological mutations underlying MLIA with associated dental anomalies. No mutations that were potentially aetiologic were identified in MSX1 and PAX9. In conclusion, this is the first report implicating coding variants in the WNT10A gene in the aetiology of MLIA. These results will require further confirmation using larger-scale studies.