Ariadne Letra

Defining Subphenotypes for Oral Clefts Based on Dental Development

Individuals with clefts present considerably more dental anomalies than do individuals without clefts. We used dental development to subphenotype clefts with the goal of identifying cleft subgroups that could have specific genetic contributions. We examined 1000 individuals, 500 with clefts and 500 without. We used several clinical features, such as cleft completeness or incompleteness, laterality, and the presence of dental anomalies to assess each individual’s cleft status. We performed chi-square and Fisher’s exact tests to compare the frequencies of observed anomalies between individuals with and individuals without clefts, and among individuals with different cleft subphenotypes. Agenesis of the lateral incisor on the non-cleft side was the most remarkable observation, and may suggest that such cases could be considered incomplete forms of bilateral clefts of the lip.

Possible Association of Amelogenin to High Caries Experience in a Guatemalan-Mayan Population

There is evidence for a genetic component in caries susceptibility, but the disease is greatly influenced by environmental factors, which are extremely difficult to control in humans. For the present study, we used DNA samples collected from 110 unrelated, non-cleft individuals older than 12 years of age from Tiquisate, Guatemala: a population with similar cultural, dietary and hygiene habits, similar access to the dentist and fluoride exposure. Forty-four individuals were designated ‘very low caries experience’ (DMFT ≤2), and 66 were designated ‘higher caries experience’ (DMFT ≧3). Single-nucleotide polymorphism markers were genotyped in selected candidate genes (ameloblastin, amelogenin, enamelin, tuftelin-1, and tuftelin interacting protein 11) that influence enamel formation. Having at least one copy of the rare amelogenin marker allele was associated with increased age-adjusted caries experience. This association was stronger in individuals with higher DMFT (DMFT ≧20; p = 0.0000001). Our results suggest that variation in amelogenin may contribute to caries susceptibility in the population studied. The approach of comparing individuals with extremely distinct caries experiences could be valuable for decreasing the potential influence of environmental factors on genetic studies of caries.

Differential Patterns of Receptor Activator of Nuclear Factor Kappa B Ligand/Osteoprotegerin Expression in Human Periapical Granulomas: Possible Association with Progressive or Stable Nature of the Lesions

Receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) are expressed in apical periodontitis, suggesting a role for these molecules during lesion development. However, the profiles of RANKL/OPG expression in periapical lesions remain unknown. In this study we investigated the patterns of RANKL and OPG mRNA expression by real-time polymerase chain reaction in human periapical granulomas (N = 44) and compared them with sites presenting characteristic bone resorbing activity: healthy (n = 14) and orthodontically stretched and compressed periodontal ligament (n = 26), healthy gingiva (n = 24), chronic gingivitis (n = 32), and chronic periodontitis (n = 34) samples. Both RANKL and OPG mRNA expression was higher in periapical granulomas when compared with healthy periodontal ligament. Distinct patterns of RANKL and OPG expression ratio were found in the granulomas and in different physiologic and pathologic conditions, with characteristic bone resorption activity potentially being indicative of the stable or progressive nature of the lesions. Lesions with radiographic image smaller than 5 mm showed higher RANKL/OPG expression than images greater than 5 mm. Periapical granulomas presented heterogeneous patterns of RANKL and OPG expression, ranging from samples with RANKL/OPG ratio similar to that seen in sites with minimal or absent bone resorption to samples with RANKL/OPG expression pattern comparable with active bone resorption sites.

Studies with Wnt Genes and Nonsyndromic Cleft Lip and Palate

BACKGROUND Clefts of the lip and/or palate (cleft lip/palate) are notable for their complex etiology. The WNT pathway regulates multiple developmental processes including craniofacial development and may play a role in cleft lip/palate and other defects of craniofacial development such as tooth agenesis. Variations in WNT genes have been recently associated with cleft lip/palate in humans. In addition, two WNT genes, Wnt3 and Wnt9B, are located in the clf1 cleft locus in mice. METHODS We investigated 13 SNPs located in Wnt3A, Wnt5A, Wnt8A, Wnt11, Wnt3, and Wnt9B genes for association with cleft lip/palate subphenotypes in 463 cleft cases and 303 unrelated controls. Genotyping of selected polymorphisms was carried out using Taqman assays. PLINK 1.06 software was used to test for differences in allele frequencies of each polymorphism between affected and unaffected individuals. Haplotype analysis was also performed. RESULTS Individuals carrying variant alleles in WNT3 presented an increased risk for cleft lip/palate (p = 0.0003; OR, 1.61; 95% CI, 1.29-2.02) in the population studied. CONCLUSION Our results continue to support a role for WNT genes in the pathogenesis of cleft lip/palate. Although much remains to be learned about the function of individual WNT genes during craniofacial development, additional studies should focus on the identification of potentially functional variants in these genes as contributors to human clefting. Birth Defects Research (Part A), 2010.

AXIN2 and CDH1 Polymorphisms, Tooth Agenesis and Oral Clefts

BACKGROUND AXIN2 and CDH1 genes play important roles during craniofacial morphogenesis. Mutations in these genes have been described in families presenting colorectal cancer and tooth agenesis, and gastric cancer and cleft lip/palate (CL/P). Oral clefts have been associated with tooth agenesis. We investigated if AXIN2 and CDH1 polymorphisms were associated with clefts or with any associated dental subphenotypes. METHODS Markers in AXIN2 and CDH1 were genotyped using Taqman chemistry in a sample cohort comprised of 500 cleft individuals and 500 unrelated controls. RESULTS Comparison between cleft and control groups showed a trend for association for AXIN2 with incomplete cleft palate (p = .006) and CDH1 with unilateral CL/P (p = .03 for left CL/P and p = .04 for right CL/P). Comparison of cleft subphenotypes with tooth agenesis and controls revealed borderline associations for CDH1 (p = .008) and AXIN2 (p = .01) with unilateral right CL/P with tooth agenesis. CONCLUSIONS We observed only borderline results for the association of AXIN2 and CDH1 with CL/P with and without tooth agenesis. Nevertheless, implication of these genes in the simultaneous occurrence of CL/P and cancer, and in tooth agenesis and cancer, is rather intriguing and warrants further investigations with other geographic and ethnic populations.

Genetic susceptibility to periapical disease: conditional contribution of MMP2 and MMP3 genes to the development of periapical lesions and healing response.

INTRODUCTION It has been proposed that individual genetic predisposition may contribute to a persistent apical periodontitis condition. Matrix metalloproteinases (MMPs) are associated with levels of inflammation and are involved in caries, pulpal, and periapical tissue destruction. MMPs also play a major role in bone resorption. In this study, we hypothesized that polymorphisms in MMP genes and their regulators may contribute to an individuals increased susceptibility to apical tissue destruction in response to deep carious lesions. METHODS Sixteen hundred radiographic records obtained through the University of Pittsburgh School of Dental Medicine Dental Registry and DNA Repository were screened for subjects with deep carious lesions in dentin with or without periapical lesions (≥ 3 mm). DNA samples of 268 patients were sorted into 2 groups: 158 cases with deep carious lesions but no periapical lesions (controls) and 110 cases with periapical lesions and deep carious lesions (cases). Sixteen SNP markers in MMP2, MMP3, MMP9, MMP13, MMP14, and TIMP2, were selected for genotyping. Genotypes were generated by endpoint analysis in a real-time polymerase chain reaction instrument. Analyses were performed comparing cases and controls. Allele and genotypic frequencies and haplotype analysis were calculated using the PLINK program. RESULTS An association was found for MMP3 rs639752 (P = .03) and rs679620 (P = .004) genotypes in individuals with periapical lesions. We also observed altered transmission of MMP2 marker haplotypes (P = .000004) in these individuals. CONCLUSIONS Variations in MMP2 and MMP3 are associated with periapical lesion formation in individuals with untreated deep carious lesions. Future studies could help predict host susceptibility to developing periapical lesions.

Interleukin-8 Gene Promoter Polymorphism (rs4073) May Contribute to Chronic Periodontitis

BACKGROUND The proinflammatory chemokine interleukin (IL)-8 is important in the regulation of the inflammatory response. Analyses of the single nucleotide polymorphism (SNP) reference sequence (rs) 4073 showed that the A allele upregulated IL-8 levels after stimulation with lipopolysaccharides. We investigated the association of the SNP rs4073 with chronic periodontitis. METHODS Genotyping was performed by a standard polymerase chain reaction-restriction fragment length polymorphism assay in 289 genomic DNA samples of healthy control subjects and patients with chronic periodontitis; analyses were adjusted by multivariate logistic regression modeling. A real-time polymerase chain reaction performance was used to detect levels of the IL-8 mRNA. RESULTS The analysis pointed to a statistically significant association of chronic periodontitis with the heterozygous TA genotype (P = 0.001); the results showed an increase in the frequency of the A allele in the diseased group (36% in the control group versus 48% in the periodontitis group). The higher levels of the IL-8 mRNA were found in the periodontitis group, mainly in individuals who presented the TA genotype (P = 0.03). CONCLUSION The SNP rs4073 was associated with chronic periodontitis in non-smoker Brazilian subjects because the frequency of the A allele was higher in the disease group than in the control group, and the TA genotype was associated with increased levels of IL-8 mRNA transcripts.

The PDGF-C regulatory region SNP rs28999109 decreases promoter transcriptional activity and is associated with CL/P

Human linkage and association studies suggest a gene(s) for nonsyndromic cleft lip with or without cleft palate (CL/P) on chromosome 4q31–q32 at or near the platelet-derived growth factor-C (PDGF-C) locus. The mouse Pdgfc−/− knockout shows that PDGF-C is essential for palatogenesis. To evaluate the role of PDGF-C in human clefting, we performed sequence analysis and SNP genotyping using 1048 multiplex CL/P families and 1000 case–control samples from multiple geographic origins. No coding region mutations were identified, but a novel −986 C>T SNP (rs28999109) was significantly associated with CL/P (P=0.01) in cases from Chinese families yielding evidence of linkage to 4q31–q32. Significant or near-significant association was also seen for this and several other PDGF-C SNPs in families from the United States, Spain, India, Turkey, China, and Colombia, whereas no association was seen in families from the Philippines, and Guatemala, and case–controls from Brazil. The −986T allele abolished six overlapping potential transcription regulatory motifs. Transfection assays of PDGF-C promoter reporter constructs show that the −986T allele is associated with a significant decrease (up to 80%) of PDGF-C gene promoter activity. This functional polymorphism acting on a susceptible genetic background may represent a component of human CL/P etiology.

The potential role of suppressors of cytokine signaling in the attenuation of inflammatory reaction and alveolar bone loss associated with apical periodontitis.

Inflammatory cytokines contribute to periapical tissue destruction. Their activity is potentially regulated by suppressors of cytokine signaling (SOCS), which downregulate signal transduction as part of an inhibitory feedback loop. We investigated the expression of the cytokines tumor necrosis factor alpha (TNF-alpha); interleukin (IL)-10 and RANKL; and SOCS-1, -2, and -3 by real-time polymerase chain reaction in 57 periapical granulomas and 38 healthy periapical tissues. Periapical granulomas exhibited significantly higher SOCS-1, -2, and -3, TNF-alpha, IL-10, and RANKL messenger RNA levels when compared with healthy controls. Significant positive correlations were found between SOCS1 and IL-10 and between SOCS3 and IL-10. Significant inverse correlations were observed between SOCS1 and TNF-alpha, SOCS1 and RANKL, and SOCS3 and TNF-alpha. Increased SOCS-1, -2, and -3 messenger RNA levels in periapical granulomas may be related to the downregulation of inflammatory cytokines in these lesions; therefore, SOCS molecules may play a role in the dynamics of periapical granulomas development.

The use of chronic gingivitis as reference status increases the power and odds of periodontitis genetic studies – a proposal based in the exposure concept and clearer resistance and susceptibility phenotypes definition

AIM Current literature on chronic periodontitis genetics encompasses numerous single nucleotide polymorphisms-focused case-control studies with inconsistent and controversial results, which typically disregards the exposure concept embraced by case-control definition. Herein, we propose a case-control design reappraisal by clear phenotype selection, where chronic gingivitis represents a genetically resistant phenotype/genotype opposing the susceptible cohort. MATERIAL AND METHODS The hypothesis was tested in healthy, chronic periodontitis and gingivitis groups through Real-time PCR-based allelic discrimination of classic variants IL1B-3954, IL6-174, TNFA-308, IL10-592 and TLR4-299. RESULTS Observed allele/genotype frequencies characterize the healthy group with an intermediate genetic profile between periodontitis and gingivitis cohorts. When comparing genotype/allele frequencies in periodontitis versus healthy and periodontitis versus gingivitis scenarios, the number of positive associations (2-4) and the degree of association (p and odds ratio values) were significantly increased by the new approach proposed (periodontitis versus gingivitis), suggesting the association of IL1B-3954, TNFA-308, IL10-592 and TLR4-299 with periodontitis risk. Power study was also significantly improved by the new study design proposed when compared to the traditional approach. CONCLUSIONS The data presented herein support the use of new case-control study design based on the case-control definition and clear resistance/susceptibility phenotypes selection, which can significantly impact the study power and odds of identification of genetic factors involved in PD.