Ultrastructural analysis of collagen fibril diameter distribution in cleft lip.

OBJECTIVE: A preliminary study to determine collagen fibril diameter (CF-ED) distribution on medial and lateral sides of cleft lip (CL). MATERIAL AND METHODS: Tissue samples from medial and lateral sides of CL were fixed in 2.5% glutaraldehyde and 1% osmium tetroxide and embedded in Araldite CY212 resin for transmission electron microscopy. The analysis of CF-ED was performed using the ImageJ program. To characterize the packaging of collagen fibrils (CFs) in the two tissues, we estimated the collagen number density (CF-ND) and fibril-area-fraction (FAF). Differences in measurements across the two sides were calculated using Wilcoxon signed-rank test. RESULTS: The CF-ED was statistically significantly (p < 0.001) smaller on the medial side (45.69 ± 7.89 nm) than on the lateral side (54.18 ± 7.62 nm). The medial side had a higher CF-ND and a higher percentage of FAF than the lateral side. CONCLUSION: Our finding of a smaller CF-ED and higher CF-ND and FAF for the medial side suggests possible differences in size and distribution of CFs between medial and lateral sides of CL. This finding provides knowledge toward underlying tissue biomechanics that may help reconstruction of perioral tissue scaffolds, ultimately resulting in better treatment of patients with oral clefts.

LINE-1 methylation in cleft lip tissues: Influence of infant MTHFR c.677C>T genotype.

OBJECTIVE: To investigate the influence of MTHFR c.677C>T genotype on LINE-1 methylation in lateral and medial tissues from cleft lip (CL). METHODS: Forty-five consecutive non-syndromic cleft lip with or without cleft palate (nsCL/P) cases were included in the study. Genomic DNA was extracted from tissues at both sides of cleft lip, and LINE-1 methylation was detected by bisulfite conversion and pyrosequencing. MTHFR c.677C>T genotyping was carried out using the TaqMan genotyping assay. RESULTS: LINE-1 methylation level was significantly higher on medial side of cleft lip compared with lateral side (p = 0.001). This difference was not significantly influenced by the case's sex or cleft type. However, MTHFR c.677C>T genotyping revealed that the difference in LINE-1 methylation across cleft lip was restricted to carriers of C allele of MTHFR c.677C>T and was not apparent in TT homozygous cases (p = 0.027). CONCLUSION: This integrated analysis supports the previous finding of differences in DNA methylation across the two sides of cleft lip and further suggests a possible role of MTHFR c.677C>T genotype in establishing this difference.

MTHFR promoter methylation might mitigate the effect of smoking at the level of LINE-1 in cleft lip tissues: A preliminary study.

BACKGROUND: The medial and maxillary aspects of the upper lip originate at separate embryonic stages and therefore may experience different maternal exposure patterns which may affect methylation. Based on this hypothesis, we investigated the level of methylation of the methylene tetrahydrofolate reductase promoter gene (mMTHFR) in tissues from cleft lip, and mMTHFR levels by MTHFR c.677C > T genotype. We further investigated whether mMTHFR mitigates the effect of smoking on long interspersed nuclear element (LINE-1) methylation in these tissues. METHODS: DNA extracted from medial and lateral tissues of 26 infants with nonsyndromic cleft lip with or without cleft palate (nsCL/P) was bisulfite converted and mMTHFR was measured on a pyrosequenser. LINE-1 methylation and MTHFR c.677C > T genotype data were obtained in our previous study. RESULTS: There was no substantial difference in mMTHFR (p = .733) and LINE-1 (p = .148) between the two tissues. mMTHFR was not influenced by MTHFR c.677C > T genotype, but there was suggestive evidence that the difference was larger among infants exposed to maternal smoking compared to nonexposed. LINE-1 methylation differences were significant (p = .025) in infants born to nonsmoking mothers, but this was not apparent (p = .872) in infants born to mothers who smoked. Our Pearson's correlation analysis suggested a weak inverse association between mMTHFR and LINE-1 (r = -.179, p = .381). CONCLUSION: Our preliminary observation of differences in patterns of mMTHFR levels in lip tissue suggests the interplay of gene and environment in the establishment of methylation in tissues at both sides of cleft lip. This requires investigation in a larger cohort, integrated with metabolic assessment.

Evaluating LINE-1 methylation in cleft lip tissues and its association with early pregnancy exposures.

AIM: To pilot investigation of methylation of long interspersed nucleotide element-1 in lip tissues from infants with nonsyndromic cleft lip, and its association with maternal periconceptional exposures. METHODS: The lateral and medial sides of the cleft lips of 23 affected infants were analyzed for long interspersed nucleotide element-1 methylation by bisulfite conversion and pyrosequencing. RESULTS: The medial side showed 1.8% higher methylation compared with the lateral side; p = 0.031, particularly in male infants (2.7% difference; p = 0.011) or when the mothers did not take folic acid during periconceptional period (2.4% difference; p = 0.011). These results were not statistically significant when Bonferroni adjustment was used. CONCLUSION: The observed differences in DNA methylation, although nonsignificant after correction for multiple comparisons, suggest that differential regulation of the two sides may impact lip fusion and warrant larger-scale replication.

Association between a common missense variant in LOXL3 gene and the risk of non-syndromic cleft palate.

To investigate possible association between functional common variants in the lysyl oxidase like 3 gene and non-syndromic cleft palate we selected a common missense variant p.Ile615Phe (rs17010021), which was predicted to have a probably damaging effect on the lysyl oxidase like 3 enzyme. We genotyped 258 non-syndromic cleft palate case-parent triads of European origin and tested genetic association using the transmission disequilibrium test and log-linear regression analyses of genotypic relative risks and of parent-of-origin effects. The observed genotype frequency in parents was in Hardy-Weinberg equilibrium. Compared with wild-type Ile/Ile homozygotes, the relative risks for Phe/Phe homozygote infants was 6.87 (P value 3.0 × 10-3 ), while that for Ile/Phe heterozygotes was not significant. Assuming an autosomal recessive model, the relative risks for Phe/Phe genotype resulted 10.54 (P value 2.9 × 10-5 ), with a 3.6% population attributable risk. No parent-of-origin effect was observed. The identification in lysyl oxidase like 3 of a missense variant which under a recessive model associates with 10-fold increased risk of non-syndromic cleft palate supports the hypothesis that the genetic etiology of this congenital anomaly includes relatively uncommon recessive variants with moderate penetrance and located in genes which are also involved in syndromes that include cleft palate as part of the phenotype. Our findings require functional validation and replication in a larger independent genetic association study.

Nonsyndromic cleft palate: An association study at GWAS candidate loci in a multiethnic sample.

BACKGROUND: Nonsyndromic cleft palate only (nsCPO) is a common and multifactorial form of orofacial clefting. In contrast to successes achieved for the other common form of orofacial clefting, that is, nonsyndromic cleft lip with/without cleft palate (nsCL/P), genome wide association studies (GWAS) of nsCPO have identified only one genome wide significant locus. Aim of the present study was to investigate whether common variants contribute to nsCPO and, if so, to identify novel risk loci. METHODS: We genotyped 33 SNPs at 27 candidate loci from 2 previously published nsCPO GWAS in an independent multiethnic sample. It included: (i) a family-based sample of European ancestry (n = 212); and (ii) two case/control samples of Central European (n = 94/339) and Arabian ancestry (n = 38/231), respectively. A separate association analysis was performed for each genotyped dataset, and meta-analyses were performed. RESULTS: After association analysis and meta-analyses, none of the 33 SNPs showed genome-wide significance. Two variants showed nominally significant association in the imputed GWAS dataset and exhibited a further decrease in p-value in a European and an overall meta-analysis including imputed GWAS data, respectively (rs395572: PMetaEU = 3.16 × 10-4 ; rs6809420: PMetaAll = 2.80 × 10-4 ). CONCLUSION: Our findings suggest that there is a limited contribution of common variants to nsCPO. However, the individual effect sizes might be too small for detection of further associations in the present sample sizes. Rare variants may play a more substantial role in nsCPO than in nsCL/P, for which GWAS of smaller sample sizes have identified genome-wide significant loci. Whole-exome/genome sequencing studies of nsCPO are now warranted.