Three novel genes tied to mandibular prognathism in eastern Mediterranean families

Genetic architecture of non-syndromic skeletal class III malocclusion

Non-syndromic skeletal Class III malocclusion is a major craniofacial disorder characterized by genetic and environmental factors. Patients with severe skeletal Class III malocclusion require orthognathic surgery to obtain aesthetic facial appearance and functional occlusion. Recent studies have demonstrated that susceptible chromosomal regions and genetic variants of candidate genes play important roles in the etiology of skeletal Class III malocclusion. Here, we provide a comprehensive review of our current understanding of the genetic factors that affect non-syndromic skeletal Class III malocclusion, including the patterns of inheritance and multiple genetic approaches. We then summarize the functional studies on related loci and genes using cell biology and animal models, which will help to implement individualized therapeutic interventions.

Towards Genetic Dissection of Skeletal Class III Malocclusion: A Review of Genetic Variations Underlying the Phenotype in Humans and Future Directions

INTRODUCTION

Skeletal abnormalities and malocclusions have varied features that impact populations globally, impairing aesthetics and lowering life quality. The prevalence of the Skeletal Class III disease is the lowest among all angle malocclusions, with varied prevalence across nations. Environmental, genetic, and societal factors play a role in its numerous etiologies. In this study, we conducted a thorough search across the published data relating to quantitative trait loci (QTL) and the genes associated with Class III progression in humans, discussed these findings and their limitations, and proposed future directions and strategies for studying this phenotype.

METHODS

An inclusive search of published papers in the PubMed and Google Scholar search engines using the following terms: 1. Human skeletal Class III; 2. Genetics of Human skeletal Class III; 3. QTL mapping and gene associated with human skeletal Class III; 4. enriched skeletal Class-III-malocclusion-associated pathways.

RESULTS

Our search has found 53 genes linked with skeletal Class III malocclusion reported in humans, genes associated with epigenetics and phenomena, and the top 20 enriched pathways associated with skeletal Class III malocclusion.

CONCLUSIONS

The human investigations yielded some contentious conclusions. We conducted a genome-wide association study (GWAS), an epigenetics-wide association study (EWAS), RNA-seq analysis, integrating GWAS and expression quantitative trait loci (eQTL), micro- and small-RNA, and long non-coding RNA analysis in tissues connected to skeletal Class III malocclusion phenotype in tissues connected with the skeletal phenotype. Finally, we invite regional, national, and international orthodontists and surgeons to join this effort by contributing human samples with skeletal Class III malocclusion following the accepted Helsinki ethical protocol to challenge these phenomena jointly.

DLX6 and MSX1 from saliva samples as potential predictors of mandibular size: A cross-sectional study

INTRODUCTION

Morphologic features of the mandible are influenced by the genes of each individual. Mandible size is important to orthodontists because the mandible is the mechanism by which the lower face influences facial esthetics and dental function. To date, no biological marker has been identified that indicates eventual mandible size. This study aimed to correlate the expression of DLX5, DLX6, EDN1, HAND2, PRRX1, and MSX1 to mandible size.

METHODS

Fifty-nine orthodontic patients aged >6 years who had available cephalometric radiographs were studied. Patients were classified on the basis of condylion-to-gnathion measurements. Messenger RNA was isolated from saliva and subjected to real-time quantitative polymerase chain reaction.

RESULTS

Threshold cycle values for subjects with small mandibles (>1 standard deviation [SD] from the mean) had the least expression of DLX6 and MSX1. Threshold cycle values for subjects with large mandibles (>1 SD) had less expression of DLX6 and MSX1 than subjects within 1 SD but more than those with small mandibles.

CONCLUSIONS

DLX6 and MSX1 are related to mandible development and size. This finding could be used to improve treatment planning for medical and dental professionals seeking to understand the impact of genetics on bone growth.

Novel genes linked to Class II Division 1 malocclusion with mandibular micrognathism

INTRODUCTION

Mandibular micrognathism (MM) is an underdeveloped mandible resulting from complex interactions between genetic and environmental factors. Prior research focused mainly on the genetic determinants of mandibular retrognathism, not necessarily reflecting micrognathism, thus supporting the need to study MM. This study aimed to explore the inheritance pattern and identify the candidate genes involved in the development and familial transmission of MM.

METHODS

Diagnosing probands with MM was based on clinical and lateral cephalometric data. The pedigrees were drawn for 11 identified families, 5 of whom accepted to undergo detailed data and biospecimen collection. These families included 15 MM and 13 non-MM subjects over 2-3 generations. The procedure involved the withdrawal of 5 mL of blood. Genomic DNA was isolated from blood cells to investigate protein-coding regions via whole exome sequencing. Standardized filtering steps were employed, and candidate genes were identified.

RESULTS

Most of the pedigrees suggested a Mendelian inheritance pattern and segregated in an autosomal-dominant manner. One of the families, which also underwent biospecimen, displayed an X-linked inheritance pattern of the trait. Genetic screening disclosed 8 potentially novel genes (GLUD2, ADGRG4, ARSH, TGIF1, FGFR3, ZNF181, INTS7, and WNT6). None of the recognized exonic regions were previously reported.

CONCLUSIONS

Eight novel genes were identified in association with MM in the largest number of families reported to date. The genes were X-linked in 1 family, a finding previously not observed in mandibular genetics.

Single nucleotide polymorphisms MYO1H 1001 C>T SNP (rs3825393) is a strong risk factor for mandibular prognathism

INTRODUCTION

Mandibular prognathism (MP) is a common craniofacial disorder of Class III malocclusion that causes esthetic and functional problems. Class III malocclusion diversity is influenced by both environmental and genetic factors. Single nucleotide polymorphisms (SNPs) in genes involved in craniofacial morphogenesis, bone and cartilage development, and metabolism, could play a role as predisposing factors. The present study aimed to establish a potential association between MATN1 -1878 A>G (rs1149048), MYO1H 1001 C>T (rs3825393), and BMP-4 538 A>G (rs17563) SNPs and MP in Serbian population.

METHODS

The study included 110 participants: 55 patients with Class III malocclusion diagnosed with MP and 55 with Class I malocclusion. The 3 SNPs were analyzed using the polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

The genotype frequency of MYO1H showed a highly significant difference between patients and controls. Heterozygous carriers of the T allele had an almost 3-fold increase in odds for the development of MP (odds ratio, 2.79; 95% confidence interval, 1.26-6.19; P = 0.010). No association could be established between MATN1 and BMP-4 polymorphisms and MP.

CONCLUSIONS

Our results support the concept of gene polymorphisms as risk modulators in mandibular prognathism development, although only the association between MYO1H and MP was found in Serbian patients with Class III malocclusion.

Genes and Pathways Associated with Skeletal Sagittal Malocclusions: A Systematic Review

Skeletal class II and III malocclusions are craniofacial disorders that negatively impact people’s quality of life worldwide. Unfortunately, the growth patterns of skeletal malocclusions and their clinical correction prognoses are difficult to predict largely due to lack of knowledge of their precise etiology. Inspired by the strong inheritance pattern of a specific type of skeletal malocclusion, previous genome-wide association studies (GWAS) were reanalyzed, resulting in the identification of 19 skeletal class II malocclusion-associated and 53 skeletal class III malocclusion-associated genes. Functional enrichment of these genes created a signal pathway atlas in which most of the genes were associated with bone and cartilage growth and development, as expected, while some were characterized by functions related to skeletal muscle maturation and construction. Interestingly, several genes and enriched pathways are involved in both skeletal class II and III malocclusions, indicating the key regulatory effects of these genes and pathways in craniofacial development. There is no doubt that further investigation is necessary to validate these recognized genes’ and pathways’ specific function(s) related to maxillary and mandibular development. In summary, this systematic review provides initial insight on developing novel gene-based treatment strategies for skeletal malocclusions and paves the path for precision medicine where dental care providers can make an accurate prediction of the craniofacial growth of an individual patient based on his/her genetic profile.

Cephalometric effects of Pushing Splints 3 compared with rapid maxillary expansion and facemask therapy in Class III malocclusion children: a randomized controlled trial

Background

Pushing Splints 3 (PS3) device was recently introduced for the treatment of Class III malocclusion in children.

Objectives

To assess the effect on the sagittal maxillary position (SNA, primary outcome) of PS3 therapy compared with rapid maxillary expansion and facemask therapy (RME/FM) and to compare skeletal and dento-alveolar effects in growing Class III patients.

Trial design

This trial was a single-centre randomized controlled trial with two groups randomly allocated in a 1:1 ratio of equal size by sealed-envelope randomization, conducted at the Dentistry Unit of Bambino Gesù Children’s Hospital, IRCCS (Rome, Italy).

Methods

A total of 48 patients with Class III malocclusion were included in the study and randomly allocated to the two groups: PS3 therapy and RME/FM therapy. Only the RME/FM group underwent palatal expansion, and both groups were instructed to wear the appliances 14 hours/day. Pre- (T0) and post-treatment (T1) cephalograms were taken. An independent sample t-test and regression analysis were used to analyse the data (P value <0.05). Researchers involved in statistics and tracings were blinded to the treatment allocation.

Results

A total of 42 patients (21 for each group) completed the study. The maxillary sagittal position improved similarly in both groups (SNA = 0.4°; P = 0.547). A statistically significant decrease of SNPg angle (−1.6°; P < 0.001) and increase of ANPg angle (1.4°; P = 0.018) were found in the RME/FM group compared with PS3 group. CoGoMe angle significantly decreased in RME/FM group compared with PS3 group (−1.7°; P = 0.042). The regression analysis showed an association between SN/MP angle at T0 and the differences between T1 and T0 of SNPg (B = 0.13; P = 0.005) and SN/MP (B = −0.19; P = 0.034). Only three patients (PS3 = 2; RME/FM = 1) had breakages of the devices.

Limitations

Results are limited to short-term effects.

Conclusion

RME/FM therapy and PS3 are both effective therapies for the early correction of Class III malocclusion. The PS3 controlled better mandibular divergency reducing the clockwise rotation in patients with higher mandibular inclination.

Registration

This study was not registered in a clinical trial registry.

Novel Sub-Clustering of Class III Skeletal Malocclusion Phenotypes in a Southern European Population Based on Proportional Measurements

Current phenotypic characterizations of Class III malocclusion are influenced more by gender or ethnic origin than by raw linear skeletal measurements. The aim of the present research is to develop a Class III skeletal malocclusion sub-phenotype characterization based on proportional cranial measurements using principal component analysis and cluster analysis. Radiometric data from 212 adult subjects (115 women and 96 men) of southern European origin affected by Class III skeletal malocclusion were analyzed. A total of 120 measurements were made, 26 were proportional skeletal measurements, which were used to perform principal component analysis and subsequent cluster analysis. The remaining 94 supplementary measurements were used for a greater description of the identified clusters. Principal component analysis established eight principal components that explained 85.1% of the total variance. The first three principal components explained 51.4% of the variance and described mandibular proportions, anterior facial height proportions, and posterior-anterior cranial proportions. Cluster analysis established four phenotypic subgroups, representing 18.4% (C1), 20.75% (C2), 38.68% (C3), and 22.17% (C4) of the sample. A new sub-clustering of skeletal Class III malocclusions that avoids gender influence is provided. Our results improve clinicians' resources for Class III malocclusion and could improve the diagnostic and treatment approaches for this malocclusion.

The presence probability of mandibular lingla and antilingula

PURPOSE

The lingula and antilingula are crucial surgical landmarks for mandibular setback surgery. The purpose of study was to investigate the correlation of presence probability between lingual and antilingula.

MATERIALS AND METHODS

A total of 180 cone-beam computed tomography sides were collected from 90 patients. The probability of absence of the lingula and antilingula was recorded with respect to the gender, mandible (unilateral and bilateral), and skeletal patterns (Class I, II, III); in addition, the correlations between these variables were analysed.

RESULTS

Of the 180 sides, 9 sides showed the absence of the lingula (5%) and 34 sides showed the absence of the antilingula (18.9%). Pearson's test revealed that the presence of the lingula and antilingula differed nonsignificantly with respect to gender and skeletal patterns, respectively. The bilateral presence of the lingula was observed in 16 sides (91.1%), and that of the antilingula was observed in 122 sides (67.8%). Pearson's test verified a significant correlation between the presence of the left and right lingula (P<0.05). By contrast, gender and skeletal patterns were nonsignificantly correlated with the presence of the lingula and antilingula. The presence of the lingula was also nonsignificantly correlated with that of the antilingula.

CONCLUSION

Gender and skeletal patterns were nonsignificantly correlated with the presence of the lingula and antilingula, respectively. The presence of the lingula was also nonsignificantly correlated with that of the antilingula. Consequently, lingula and antilingula cannot serve as the absolute standards for mandibular setback surgery.