A missense mutation in DUSP6 is associated with Class III malocclusion

Skeletal Class III phenotype: Link between animal models and human genetics: A scoping review

This study aimed to identify evidence from animal studies examining genetic variants underlying maxillomandibular discrepancies resulting in a skeletal Class III (SCIII) malocclusion phenotype. Following the Manual for Evidence Synthesis of the JBI and the PRISMA extension for scoping reviews, a participant, concept, context question was formulated and systematic searches were executed in the PubMed, Scopus, WOS, Scielo, Open Gray, and Mednar databases. Of the 779 identified studies, 13 met the selection criteria and were included in the data extraction. The SCIII malocclusion phenotype was described as mandibular prognathism in the Danio rerio, Dicentrarchus labrax, and Equus africanus asinus models; and as maxillary deficiency in the Felis silvestris catus, Canis familiaris, Salmo trutta, and Mus musculus models. The identified genetic variants highlight the significance of BMP and TGF-β signaling. Their regulatory pathways and genetic interactions link them to cellular bone regulation events, particularly ossification regulation of postnatal cranial synchondroses. In conclusion, twenty genetic variants associated with the skeletal SCIII malocclusion phenotype were identified in animal models. Their interactions and regulatory pathways corroborate the role of these variants in bone growth, differentiation events, and ossification regulation of postnatal cranial synchondroses.

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.

Missense polymorphisms potentially involved in mandibular prognathism

Objective

The current study aimed to identify and analyze missense single nucleotide polymorphisms (SNPs) that can potentially cause mandibular prognathism.

Methods

After reviewing the articles, 56 genes associated with mandibular prognathism were identified and their missense SNPs were retrieved from the NCBI website. Several web-based tools including CADD, PolyPhen-2, PROVEAN, SNAP2, PANTHER, FATHMM, and PON-P2 were used to filter out harmful SNPs. Additionally, ConSurf determined the level of evolutionary conservation at positions where SNPs occur. I-Mutant2 and MUpro predicted the effect of SNPs on protein stability. Furthermore, to investigate the structural and functional changes of proteins, HOPE and LOMETS tools were utilized.

Results

Based on predictions in at least four web-based tools, the results indicated that PLXNA2-rs4844658, DUSP6-rs2279574, and FBN3-rs33967815 are harmful. These SNPs are located at positions with variable or average conservation and have the potential to reduce the stability of their respective proteins. Moreover, they may impair protein activity by causing structural and functional changes.

Conclusions

In this study, we identified PLXNA2-rs4844658, DUSP6-rs2279574, and FBN3-rs33967815 as potential risk factors for mandibular prognathism using several web-based tools. According to the possible roles of PLXNA2, DUSP6, and FBN3 proteins in ossification pathways, we recommend that these SNPs be investigated further in experimental research. Through such studies, we hope to gain a better understanding of the molecular mechanisms involved in mandible formation.

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.

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.

Skeletal Class III Malocclusion Is Associated with ADAMTS2 Variants and Reduced Expression in a Familial Case

Skeletal Class III malocclusion with maxillary deficiency is a severe maxillofacial disease with unclear pathogenic mechanisms. We recruited a Han Chinese family who was clinically diagnosed with skeletal Class III malocclusion and maxillary deficiency. Using whole exome sequencing, a missense variant in ADAMTS2 (NM_014244: c.3506G>T: p.G1169V) was identified and predicted as deleterious by in silico tools. We also found ADAMTS2 variants associated with deficient maxillary development in a cohort. ADAMTS2 expression in HEK293 cells showed significant decrease due to the variant, which was also consistent in dental pulp stem cells from the proband and a healthy control. In the adamts2-knockdown zebrafish model, the length and width of the ethmoid plate, as well as the length of the palatoquadrate became significantly shorter than the control group (p < 0.001), while there was no significant difference in the length and width of the mandible. The expression of Sox3, which was required in early embryonic craniofacial development, was significantly downregulated in the adamts2-knockdown zebrafish embryos. Bioinformatic and cellular studies showed that the decreased expression of ADAMTS2 may inhibit downstream ErbB signaling pathway transduction and restrain subsequent osteogenesis in human adult mesenchymal stromal cells. Collectively, these data showed that ADAMTS2 (c.3506G>T: p.G1169V) may confer susceptibility to risk of skeletal Class III malocclusion with maxillary deficiency.

Number of Teeth Is Related to Craniofacial Morphology in Humans

Simple Summary

In modern humans, congenital absence of one or more permanent teeth has a prevalence of 22.6% when considering the third molars and of 6.4% when not. Its high prevalence, in conjunction with evolutionary findings pinpointing to a steady reduction in teeth number, raises the question whether the congenital absence of teeth in modern humans is an evolutionary trend rather than an anomaly. Previous studies have shown that modern humans with less teeth also have smaller faces; however, the association between teeth number and craniofacial morphology remains unclear. Here, we show that less teeth are associated with a flatter profile and a decreased facial height. These findings support the claim of a broader relationship between number of teeth and overall craniofacial development and have evolutionary implications, since face reduction comprises also an evolutionary trend in humans.

Abstract

One of the most common dental anomalies in humans is the congenital absence of teeth, referred to as tooth agenesis. The association of tooth agenesis to craniofacial morphology has been previously investigated but remains unclear. We investigated this association by applying geometric morphometric methods in a large sample of modern humans. In line with previous studies, we report here that a reduced teeth number is linked to a less convex profile, as well as to a shorter face. The effects were similar for males and females; they increased as the severity of the tooth agenesis increased and remained unaltered by the inclusion of third molars and of allometry in the analysis. Furthermore, in cases with tooth agenesis only in the maxilla, there was no detectable effect in mandibular shape, whereas maxillary shape was affected independently of the location of missing teeth. The robustness of the present sample along with the shape analysis and the statistical approach applied, allowed for thorough testing of various contributing factors regarding the presence but also the magnitude of effects. The present findings suggest a relationship between number of teeth and overall craniofacial development and have evolutionary implications.

Candidate positive targets of LHX6 and LHX8 transcription factors in the developing upper jaw

Craniofacial development is controlled by a large number of genes, which interact with one another to form a complex gene regulatory network (GRN). Key components of GRN are signaling molecules and transcription factors. Therefore, identifying targets of core transcription factors is an important part of the overall efforts toward building a comprehensive and accurate model of GRN. LHX6 and LHX8 are transcription factors expressed in the oral mesenchyme of the first pharyngeal arch (PA1), and they are crucial regulators of palate and tooth development. Previously, we performed genome-wide transcriptional profiling and chromatin immunoprecipitation to identify target genes of LHX6 and LHX8 in PA1, and described a set of genes repressed by LHX. However, there has not been any discussion of the genes positively regulated by LHX6 and LHX8. In this paper, we revisited the above datasets to identify candidate positive targets of LHX in PA1. Focusing on those with known connections to craniofacial development, we performed RNA in situ hybridization to confirm the changes in expression in Lhx6;Lhx8 mutant. We also confirmed the binding of LHX6 to several putative enhancers near the candidate target genes. Together, we have uncovered novel connections between Lhx and other important regulators of craniofacial development, including Eya1, Barx1, Rspo2, Rspo3, and Wnt11.

Analysis of MYO1H Gene Polymorphism in Skeletal Class-III Malocclusion Due to Mandibular Prognathism

Background  Mandibular prognathism (MP) is a craniofacial deformity resulting from the combined effects of environmental and genetic factors. Although various linkage and genome-wide association studies for mandibular prognathism have identified multiple strongly associated regions and genes, the causal genes and variants responsible for the deformity remained ambiguous.

Aim  This research work was aimed to study the association between polymorphism rs10850110 of the MYO1H gene and skeletal class-III malocclusion in our local population.

Materials and Methods  Thirty patients with skeletal class III due to mandibular prognathism in the study group and 30 patients with skeletal class I in the control group were selected for this study. These patients were from both sexes and above age 10 years. Based on the cephalometric values, patients were categorized into study and control groups. SNB (angle between sella, nasion and point B at nasion) greater than 82 degrees with an ANB (angle between point A, nasion and point B at nasion) of less than 0 degrees in the study group and ANB (angle between point A, nasion and point B at nasion) of 2 to 4 degrees in the control group were categorized. The polymorphism (rs10850110) of the MYO1H gene was genotyped using polymerase chain reaction and restriction fragment length polymorphism. Associations were tested with SNP exact test using SNPstats software.

Results  The single-nucleotide polymorphism rs10850110 showed a statistically significant association with mandibular prognathism. The G allele of marker rs10850110 (5′ of myosin1H - MYO1H ) was overrepresented when compared with the “A” allele in mandibular prognathism cases ( p  < 0.0001), and this was very significant.

Conclusion  These results suggest that the rs10850110 polymorphism of the MYO1H gene is associated with an increased risk for mandibular prognathism.

Genetic effect of single nucleotide polymorphisms in growth hormone receptor gene on the risk of non-syndromic mandibular prognathism in the Korean population

OBJECTIVES

To evaluate the association of three single-nucleotide polymorphisms (SNPs) of growth hormone receptor (GHR) gene with mandibular prognathism (MP) and relationships between mandibular morphology and GHR gene SNPs in the Korean population.

MATERIALS AND METHODS

A total of 325 subjects were divided into two groups based on sagittal maxillomandibular relationship by the lateral cephalography: the MP and control groups. From the SNPs in the GHR gene, three SNPs (rs6180, rs6182 and rs6184) were selected. SNP genotyping was performed using direct sequencing. The craniofacial measurements of lateral cephalography were analysed.

RESULTS

We found a lack of association between GHR and MP. However, in the analysis according to the values of cephalometric measurements, rs6180 was significantly associated with ANB, SNB, effective mandibular length and SNMP in females. Additionally, rs6182 and rs6184 were significantly associated with ramal height in males.

CONCLUSION

Growth hormone receptor SNPs may affect not only the sagittal development of mandible but also the vertical development of ramal height, and GHR SNPs may gender-differently influence mandibular morphology. This finding supports that the GHR might be susceptible on mandibular morphogenesis in the Korean population.

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.

Methods in Genetic Analysis for Evaluation Mandibular Shape and Size Variations in Human Mandible

ABSTRACT

The human mandible has been investigated from both clinical and evolutionary perspectives. Recent advances in genome science have identified the genetic regulation of human mandibular shape and size. Identification of genes that regulate mandibular shape and size would not only enhance our understanding of the mechanisms of mandibular growth and development but also help define a strategy to prevent mandibular dysplasia. This review provides a comprehensive summary of why and how the mandible was evaluated in the human mandible genome study. The variation in human mandibular shape and size has been progressively clarified, not only by focusing on the mandible alone but also by using extremely diverse approaches. The methods of data acquisition for evaluating human mandibular shape and size variation are well established. Furthermore, this review explains how to proceed with future research.

Genetics of Dentofacial and Orthodontic Abnormalities

The development of craniofacial complex and dental structures is a complex and delicate process guided by specific genetic mechanisms. Genetic and environmental factors can influence the execution of these mechanisms and result in abnormalities. An insight into the mechanisms and genes involved in the development of orofacial and dental structures has gradually gained by pedigree analysis of families and twin studies as well as experimental studies on vertebrate models. The development of novel treatment techniques depends on in-depth knowledge of the various molecular or cellular processes and genes involved in the development of the orofacial complex. This review article focuses on the role of genes in the development of nonsyndromic orofacial, dentofacial variations, malocclusions, excluding cleft lip palate, and the advancements in the field of molecular genetics and its application to obtain better treatment outcomes.

Genetic factors contributing to skeletal class III malocclusion: a systematic review and meta-analysis

OBJECTIVES

The present systematic review aims to report and critically assess the findings of the available scientific evidence from genetic association studies examining the genetic variants underlying skeletal class III malocclusion and its sub-phenotypes.

MATERIAL AND METHODS

A pre-piloted protocol was registered and followed. The PubMed, Scopus, WOS, Cochrane Library, Gray Open literature, and CADTH databases were explored for genetic association studies following PICOS-based selection criteria. The research was reported in accordance with PRISMA statement and HuGE guidelines. The Q-genie tool was applied to assess the quality of genetic studies. Meta-analysis of genetic association studies was done by means of Meta-Genyo tool.

RESULTS

A total of 8258 articles were retrieved, of which 22 were selected for in-depth analysis. Most of the studies did not differentiate between sub-phenotypes, and the cohorts were heterogeneous regarding ethnicity. Four to five principal components of class III malocclusion explained the phenotypic variation, and gene variants at MYO1H(rs10850110), BMP3(rs1390319), GHR (rs2973015,rs6184, rs2973015), FGF7(rs372127537), FGF10(rs593307), and SNAI3(rs4287555) (p < .05) explained most of the variation across the studies, associated to vertical, horizontal, or combined skeletal discrepancies. Meta-analysis results identified a statistically significant association between risk of class III malocclusion of A allele of the FBN3 rs7351083 [OR 2.13; 95% CI 1.1-4.1; p 0.02; recessive model].

CONCLUSION

Skeletal class III is a polygenic trait substantially modulated by ethnicity. A multicentric approach should be considered in future studies to increase sample sizes, applying multivariate analysis such as PCA and cluster analysis to characterize existing sub-phenotypes warranting a deeper analysis of genetic variants contributing to skeletal class III craniofacial disharmony.

CLINICAL RELEVANCE

Grasping the underlying mechanisms of this pathology is critical for a fuller understanding of its etiology, allowing generation of preventive strategies, new individualized therapeutic approaches and more accurate treatment planification strategies.

Identification of pathogenic variants of ERLEC1 in individuals with Class III malocclusion by exome sequencing

Class III malocclusion is a common dentofacial deformity. The underlying genetic alteration is largely unclear. In this study, we sought to determine the genetic etiology for Class III malocclusion. A four-generation pedigree of Class III malocclusion was recruited for exome sequencing analyses. The likely causative gene was verified via Sanger sequencing in an additional 90 unrelated sporadic Class III malocclusion patients. We identified a rare heterozygous variant in endoplasmic reticulum lectin 1 (ERLEC1; NM_015701.4(ERLEC1_v001):c.1237C>T, p.(His413Tyr), designated as ERLEC1-m in this article) that cosegregated with the deformity in pedigree members and three additional rare missense heterozygous variants (c.419C>G, p.(Thr140Ser), c.419C>T, p.(Thr140Ile), and c.1448A>G, p.(Asn483Ser)) in 3 of 90 unrelated sporadic subjects. Our results showed that ERLEC1 is highly expressed in mouse jaw osteoblasts and inhibits osteoblast proliferation. ERLEC1-m significantly enhanced this inhibitory effect of osteoblast proliferation. Our results also showed that the proper level of ERLEC1 expression is crucial for proper osteogenic differentiation. The ERLEC1 variant identified in this study is likely a causal mutation of Class III malocclusion. Our study reveals the genetic basis of Class III malocclusion and provides insights into the novel target for clinical management of Class III malocclusion, in addition to orthodontic treatment and orthodontic surgery.

A Bayesian network meta-analysis of orthopaedic treatment in Class III malocclusion: Maxillary protraction with skeletal anchorage or a rapid maxillary expander

To evaluate and compare the effectiveness of orthopaedic treatment for Class III malocclusions using skeletal anchorage or a rapid maxillary expander for maxillary protraction. Electronic databases, including PubMed, EMBASE, Cochrane Library and Web of Science, were searched for randomized controlled trials (RCTs) and non-randomized clinical trials (CCTs) for orthopaedic treatment of Class III malocclusions. Five interventions were studied: a facemask with a maxillary temporary anchorage device (MTAD), a bone-anchored rapid maxillary expansion (BARME), a rapid maxillary expansion (RME), an alternate rapid maxillary expansion and contraction (Alt-RAMEC), and a bone-anchored intermaxillary traction (BAIMT). Eight outcomes (SNA, SNB, ANB, overjet, SN-GoGn, ANS-Me, IMPA (L1-MP), and U1-PP) were statistically polled. We conducted network meta-analysis using R statistical software with the GeMTC package. Twenty-five studies met the inclusion criteria. Compared with the RME group, the Alt-RAMEC group (mean difference (MD): 1.3; 95% credibility interval (CrI): 0.26, 2.3) and MTAD group (MD: 0.85; 95% CrI: 0.065, 1.6) showed a better effect on ANB in CCTs. Regarding the vertical relationship, the BAIMT group (MD: -2.2; 95% CrI: -5.2, 0.73) showed a smaller effect regarding increasing the vertical dimension of ANS-Me. The RME, MTAD and Alt-RAMEC group showed a higher ability to decrease the angle of L1-MP. The Alt-RAMEC and MTAD protocol have a higher possibility to obtain a skeletal and tooth effect in sagittal relationships. The BAIMT protocol can acquire a better skeletal effect in sagittal relationships with less vertical and dental changes. More well-designed RCTs are needed to ensure that the conclusion is reliable.

Three novel genes tied to mandibular prognathism in eastern Mediterranean families

INTRODUCTION

Mandibular prognathism (MP) is subject to major polygenic influence and segregates within families in autosomal dominance with variable expressivity and incomplete penetrance. We aimed to identify the inheritance pattern and genes and loci involved in the development of MP in Mediterranean families and to evaluate the dentoskeletal characteristics of affected individuals.

METHODS

Fifty-one eastern Mediterranean families with individuals affected by MP were identified. Data and biospecimens were collected from 14 of the families, including clinical examination, lateral cephalography (on subjects with Class III malocclusion), and 5 mL blood drawn from consenting affected and nonaffected relatives. Next-generation sequencing (NGS) was performed on 8 families (7 Lebanese, 1 Lebanese/Syrian), including large numbers of affected individuals over many generations and severe conditions, with the use of whole-exome sequencing.

RESULTS

Most pedigrees suggested autosomal-dominant inheritance with an equal number of affected male and female individuals. Affected individuals had macrognathic and prognathic mandibles with dentoalveolar compensation. Genetic screening did not correspond with previously reported MP-linked genes, but yielded 3 novel genes (C1orf167, NBPF8, NBPF9) on chromosome 1 potentially responsible for mandibular development and macrognathism.

CONCLUSIONS

In this first genetic study with the use of NGS on the largest reported number of families with MP, novel genes (C1orf167, NBPF8, NBPF9) were associated with familial MP in the eastern Mediterranean population.

Whole-exome sequencing in a Japanese pedigree implicates a rare non-synonymous single-nucleotide variant in BEST3 as a candidate for mandibular prognathism

Mandibular prognathism is a phenotype of facial deformity seen in populations around the world, but with higher incidence among East Asian populations. Five genome-wide nonparametric linkage analyses and a genome-wide association study to identify susceptibility loci of the phenotype have shown inconsistent results. To explore variants related to mandibular prognathism, we undertook whole-exome sequencing in a Japanese pedigree. The pedigree was ascertained as mandibular prognathism. The pedigree comprised 15 individuals from 4 generations. Four affected individuals across 2 generations and 5 unaffected individuals were chosen for whole-exome sequencing. Five non-synonymous single-nucleotide variants (SNVs) of UBASH3B, OR6M1, OR8D4, OR8B4, and BEST3 genes were detected in all 4 affected individuals, but in none of the 5 unaffected individuals. A non-synonymous SNV of the BEST3 gene, Chr12(GRCh37):g.70048878G>T, NM_032735.2:c.1816C>A, p.(L606I), was identified as rare missense variant. BEST3 is located on chromosome 12q15 and encodes bestrophin 3 from the bestrophin family of anion channels. The 4 other non-synonymous SNVs of UBASH3B, OR6M1, OR8D4, and OR8B4 were not considered plausible candidates for mandibular prognathism. Our whole-exome sequencing implicates a rare non-synonymous SNV of BEST3 as a candidate for mandibular prognathism in the Japanese pedigree.

Craniofacial, orofacial and dental disorders: the role of the RAS/ERK pathway

Deviations from the precisely coordinated programme of human head development can lead to craniofacial and orofacial malformations often including a variety of dental abnormalities too. Although the aetiology is still unknown in many cases, during the last decades different intracellular signalling pathways have been genetically linked to specific disorders. Among these pathways, the RAS/extracellular signal-regulated kinase (ERK) signalling cascade is the focus of this review since it encompasses a large group of genes that when mutated cause some of the most common and severe developmental anomalies in humans. We present the components of the RAS/ERK pathway implicated in craniofacial and orodental disorders through a series of human and animal studies. We attempt to unravel the specific molecular targets downstream of ERK that act on particular cell types and regulate key steps in the associated developmental processes. Finally we point to ambiguities in our current knowledge that need to be clarified before RAS/ERK-targeting therapeutic approaches can be implemented.

Systematic review of hormonal and genetic factors involved in the nonsyndromic disorders of the lower jaw

Mandibular disorders are among the most common birth defects in humans, yet the etiological factors are largely unknown. Most of the neonates affected by mandibular abnormalities have a sequence of secondary anomalies, including airway obstruction and feeding problems, that reduce the quality of life. In the event of lacking corrective surgeries, patients with mandibular congenital disorders suffer from additional lifelong problems such as sleep apnea and temporomandibular disorders, among others. The goal of this systematic review is to gather evidence on hormonal and genetic factors that are involved in signaling pathways and interactions that are potentially associated with the nonsyndromic mandibular disorders. We found that members of FGF and BMP pathways, including FGF8/10, FGFR2/3, BMP2/4/7, BMPR1A, ACVR1, and ACVR2A/B, have a prominent number of gene-gene interactions among all identified genes in this review. Gene ontology of the 154 genes showed that the functional gene sets are involved in all aspects of cellular processes and organogenesis. Some of the genes identified by the genome-wide association studies of common mandibular disorders are involved in skeletal formation and growth retardation based on animal models, suggesting a potential direct role as genetic risk factors in the common complex jaw disorders. Developmental Dynamics 248:162-172, 2019. © 2018 Wiley Periodicals, Inc.

Part II: Temporomandibular Joint (TMJ)-Regeneration, Degeneration, and Adaptation

PURPOSE OF REVIEW

Elucidate temporomandibular joint (TMJ) development and pathophysiology relative to regeneration, degeneration, and adaption.

RECENT FINDINGS

The pharyngeal arch produces a highly conserved stomatognathic system that supports airway and masticatory function. An induced subperiosteal layer of fibrocartilage cushions TMJ functional and parafunctional loads. If the fibrocartilage disc is present, a fractured mandibular condyle (MC) regenerates near the eminence of the fossa via a blastema emanating from the medial periosteal surface of the ramus. TMJ degenerative joint disease (DJD) is a relatively painless osteoarthrosis, resulting in extensive sclerosis, disc destruction, and lytic lesions. Facial form and symmetry may be affected, but the residual bone is vital because distraction continues to lengthen the MC with anabolic bone modeling. Extensive TMJ adaptive, healing, and regenerative potential maintains optimal, life support functions over a lifetime. Unique aspects of TMJ development, function, and pathophysiology may be useful for innovative management of other joints.

Identification and Functional Studies of MYO1H for Mandibular Prognathism

Mandibular prognathism (MP) is regarded as a craniofacial deformity resulting from the combined effects of environmental and genetic factors, while the genetically predetermined component is considered to play an important role to develop MP. Although linkage and association studies for MP have identified multiple strongly associated regions and genes, the causal genes and variants responsible for the deformity remain largely undetermined. To address this, we performed targeted sequencing of 396 genes selected from previous studies as well as genes and pathways related with craniofacial development as primary candidates in 199 MP cases and 197 controls and carried out a series of statistical and functional analyses. A nonsynonymous common variant of MYO1H rs3825393, C>T, p.Pro1001Leu, was identified to be significantly associated with MP. During zebrafish embryologic development, expression of MYO1H orthologous genes were detected at mandibular jaw. Furthermore, jaw cartilage defects were observed in zebrafish knockdown models. Collectively, these data demonstrate that MYO1H is required for proper jaw growth and contributes to MP pathogenesis, expanding our knowledge of the genetic basis of MP.

Genetic Factors Involved in Mandibular Prognathism

Mandibular prognathism is defined as an abnormal forward projection of the mandible beyond the standard relation to the cranial base and it is usually categorized as both a skeletal Class III pattern and Angle Class III malocclusion. The etiology of mandibular prognathism is still uncertain, with various genetic, epigenetic, and environmental factors possibly involved. However, many reports on its coexistence in both twins and segregation in families suggest the importance of genetic influences. A multifactorial and polygenic background with a threshold for expression or an autosomal dominant mode with incomplete penetrance and variable expressivity are the most probable inheritance patterns. Linkage analyses have, thus far, shown the statistical significance of such loci as 1p22.1, 1p22.3, 1p32.2, 1p36, 3q26.2, 4p16.1, 6q25, 11q22, 12pter-p12.3, 12q13.13, 12q23, 12q24.11, 14q24.3 to 31.2, and 19p13.2. The following appear among candidate genes: MATN1, EPB41, growth hormone receptor, COL2A1, COL1A1, MYO1H, DUSP6, ARHGAP21, ADAMTS1, FGF23, FGFR2, TBX5, ALPL, HSPG2, EVC, EVC2, the HoxC gene cluster, insulin-like growth factor 1, PLXNA2, SSX2IP, TGFB3, LTBP2, MMP13/CLG3, KRT7, and FBN3. On the other hand, MYH1, MYH2, MYH3, MYH7, MYH8, FOXO3, NFATC1, PTGS2, KAT6B, HDAC4, and RUNX2 expression is suspected to be involved in the epigenetic regulations behind the mandibular prognathism phenotype.

Heredity, Genetics and Orthodontics - How Much Has This Research Really Helped?

Uncovering the genetic factors that correlate with a clinical deviation of previously unknown etiology helps to diminish the unknown variation influencing the phenotype. Clinical studies, particularly those that consider the effects of an appliance or treatment regimen on growth, need to be a part of these types of genetic investigations in the future. While the day-to-day utilization of "testing" for genetic factors is not ready for practice yet, genetic testing for monogenic traits such as Primary Failure of Eruption (PFE) and Class III malocclusion is showing more promise as knowledge and technology advances. Although the heterogeneous complexity of such things as facial and dental development, the physiology of tooth movement, and the occurrence of External Apical Root Resorption (EARR) make their precise prediction untenable, investigations into the genetic factors that influence different phenotypes, and how these factors may relate to or impact environmental factors (including orthodontic treatment) are becoming better understood. The most important "genetic test" the practitioner can do today is to gather the patient's individual and family history. This would greatly benefit the patient, and augment the usefulness of these families in future clinical research in which clinical findings, environmental, and genetic factors can be studied.

Genome-wide association study for mandibular prognathism using microsatellite and pooled DNA method

INTRODUCTION

The purpose of this study was to extend an association study from chromosome 1 to the whole genome (genome-wide association study) to find susceptibility loci of mandibular prognathism.

METHODS

Two hundred forty patients diagnosed with mandibular prognathism and 360 healthy controls of Japanese descent were recruited. The typing of microsatellites covering the whole genome was conducted using a pooled DNA method. Upon completion of the first and second screenings with pooled DNA, the positive microsatellite markers from both the first and second typings were retyped using individual-subject DNA samples to confirm the significance of allele frequency.

RESULTS

Six microsatellites (D1S0411i, D1S1358i, D3S0810i, D6S0827i, D7S0133i, and D15S0154i) showed differences between allele frequencies of the subjects and controls at P <0.001. D1S0411i, D1S1358i, D3S0810i, D6S0827i, D7S0133i, and D15S0154i were located on chromosomes 1p22.3, 1q32.2, 3q23, 6q23.2, 7q11.22, and 15q22.22, respectively. SSX2IP, PLXNA2, RASA2, TCF21, CALN1, and RORA were suggested as candidate genes.

CONCLUSIONS

The genome-wide association study using microsatellites suggested that 6 loci (1p22.3, 1q32.2, 3q23, 6q23.2, 7q11.22, and 15q22.22) were susceptibility regions of mandibular prognathism. The locus 1p22.3 was supported by a previous linkage analysis, and the other 5 were novel loci.

Expressional Analysis of MSX1 (Human) Revealed its Role in Sagittal Jaw Relationship

INTRODUCTION

Abnormal skeletal jaw relationships is an important factor causing difficulty in speech, mastication, sleep and social interaction, thus affect the overall well being of an individual.

AIM

The present study was an attempt to decipher the role of human MSX1 in terms of sagittal jaw relationship by employing Polymerase Chain Reaction (PCR) based analysis.

MATERIALS AND METHODS

Ninety-eight case subjects belonging to North India with skeletal Class II and Class III jaw relationships were selected. Further, thirty-five control subjects of the same region having Class I skeletal and dental relationships (normal Jaw relationships) with good alignment of all teeth were enrolled. MSX1 gene sequencing was performed using the subjects' blood samples. Multiple sequence alignment was performed to find Single Nucleotide Polymorphisms (SNP's). Nine SNP's were obtained of which seven were reported and two novels. Statistical analysis was performed using Chi square test to compare genotype differences between case and control groups.

RESULTS

SNP rs186861426 was found to be significantly associated in Class I subjects (p-value=0.02). The sequencing results suggested that individuals having changes from G (guanosine) with A (adenine) genotype had approximately seven times low risk for developing Class II division 1 malocclusion as compared to those alleles having GG genotype and therefore, allele 'A' position on chromosome 4 (rs186861426) seems to have a protective role.

CONCLUSION

The study unfolds an important relationship between MSX1 gene and Class II division 1 malocclusion and Class I normal skeletal relationships. The study tried to interpret the role of human MSX1 and extend the gene pool responsible for the skeletal anomalies related to development of abnormal upper and lower jaws.

Targeted sequencing in FGF/FGFR genes and association analysis of variants for mandibular prognathism

To identify variants of the genes in fibroblast growth factors/fibroblast growth factor receptors (FGF/FGFR) signal pathway that predispose to mandibular prognathism (MP) in the general Chinese population systematically.Targeted sequencing of the FGF/FGFR genes was conducted in 176 MP individuals and 155 class I malocclusion controls. The associations of common and rare variants with MP as a categorical phenotype and also continuous malocclusion phenotypes generated by principal component (PC) analysis were analyzed.One common variant, rs372127537, located in the 3'-untranslated region of FGF7 gene, was significantly related to PC1 (P  =  4.22 × 10), which explained 23.23% of the overall phenotypic variation observed and corresponded to vertical discrepancies ranging from short anterior face height to long anterior face height, after Bonferroni correction. Also, 15 other variants were associated with PC1-4, although not significant after multiple corrections (P < .05). We also identified 3 variants: rs13317 in FGFR1, rs149242678 in FGF20, and rs79176051 FGF12 associated with MP (P < .05). With respect to rare variant analysis, variants within the FGF12 gene showed significant association with MP (P  =  .001).Association between FGF/FGFR signaling pathway and MP has been identified. We found a previously unreported SNP in FGF7 significantly related to increased facial height. Also, rare variants within the FGF12 were associated with MP. Our results provide new clues for genetic mechanisms of MP and shed light on strategies for evaluating rare variants that underlie complex traits. Future studies with larger sample sizes and more comprehensive genome coverage, and also in other population are required to replicate these findings.

Genetic Etiology in Nonsyndromic Mandibular Prognathism

Mandibular prognathism (MP) is considered to be a cranial-facial disorder resulting from the interaction between genes and environment. Recent studies have demonstrated that susceptible chromosomal regions and candidate genes may be responsible for MP. In this study, the authors present current views on the effect of genetic components in nonsystematic mandibular prognathism, in order to clarify the genetic etiology of MP. Data source were Electronic databases, manual searching, and reference lists checking, up to April 2016. Study selection, level of evidence assessment, and data extraction were done by 2 individuals in duplicate. Ninety-one studies were retrieved in initial electronic and manual search, and based on the established inclusion and exclusion criteria, 15 were selected for the review. In result, loci 1p36, 1q32.2, 1p22.3, 4p16.1, 6q25, 19p13, 14q24.3, 14q31.1, and 14q31.2 were thought to harbor genes that confer susceptibility to MP. Genes Matrilin-1, ADAMTS1, COL2A1, and EPB41 seemed to be strongly associated with MP while gene of growth hormone receptor was in dispute. Genetic components appeared to be associated with MP. However, in view of the variety of populations and results in related publications, further studies are necessary to clarify the genetic etiology of MP.

Candidate gene analyses of 3-dimensional dentoalveolar phenotypes in subjects with malocclusion

INTRODUCTION

Genetic studies of malocclusion etiology have identified 4 deleterious mutations in genes DUSP6,ARHGAP21, FGF23, and ADAMTS1 in familial Class III cases. Although these variants may have large impacts on Class III phenotypic expression, their low frequency (<1%) makes them unlikely to explain most malocclusions. Thus, much of the genetic variation underlying the dentofacial phenotypic variation associated with malocclusion remains unknown. In this study, we evaluated associations between common genetic variations in craniofacial candidate genes and 3-dimensional dentoalveolar phenotypes in patients with malocclusion.

METHODS

Pretreatment dental casts or cone-beam computed tomographic images from 300 healthy subjects were digitized with 48 landmarks. The 3-dimensional coordinate data were submitted to a geometric morphometric approach along with principal component analysis to generate continuous phenotypes including symmetric and asymmetric components of dentoalveolar shape variation, fluctuating asymmetry, and size. The subjects were genotyped for 222 single-nucleotide polymorphisms in 82 genes/loci, and phenotpye-genotype associations were tested via multivariate linear regression.

RESULTS

Principal component analysis of symmetric variation identified 4 components that explained 68% of the total variance and depicted anteroposterior, vertical, and transverse dentoalveolar discrepancies. Suggestive associations (P < 0.05) were identified with PITX2, SNAI3, 11q22.2-q22.3, 4p16.1, ISL1, and FGF8. Principal component analysis for asymmetric variations identified 4 components that explained 51% of the total variations and captured left-to-right discrepancies resulting in midline deviations, unilateral crossbites, and ectopic eruptions. Suggestive associations were found with TBX1AJUBA, SNAI3SATB2, TP63, and 1p22.1. Fluctuating asymmetry was associated with BMP3 and LATS1. Associations for SATB2 and BMP3 with asymmetric variations remained significant after the Bonferroni correction (P <0.00022). Suggestive associations were found for centroid size, a proxy for dentoalveolar size variation with 4p16.1 and SNAI1.

CONCLUSIONS

Specific genetic pathways associated with 3-dimensional dentoalveolar phenotypic variation in malocclusions were identified.

Genetic polymorphisms underlying the skeletal Class III phenotype

INTRODUCTION

Our goal was to verify the association between candidate polymorphisms and skeletal Class III malocclusion in a well-characterized homogeneous sample set.

METHODS

Thirty-five single-nucleotide polymorphisms were studied from 10 candidate loci in 54 Class III subjects and 120 controls. Skeletal Class III characteristics included ANB angle less than 0°, SNB angle greater than 83° (mandibular prognathism), SNA angle less than 79° (maxillary deficiency), Class III molar relationship, and negative overjet. Inclusion criteria for the controls were ANB angle between 0° and 4°, Class I molar relationship, and normal overjet. Chi-square and Fisher exact tests and principal component (PC) analysis were used to determine overrepresentation of marker alleles with alpha of 0.05. Odds ratios and 95% confidence intervals were calculated.

RESULTS

MYO1H (rs10850110 A<G) (P <0.01; odds ratio, 7.44 [4.02-13.77]) was associated with an increased risk for the mandibular prognathism phenotype. These results were confirmed by PC analysis, which showed 4 PCs representing the sample variations (PC1, 37.24%; PC2, 20.02%; PC3, 12.18%; and PC4, 11.40%), and PC1 was associated with MYO1H (P <0.001). We also found by PC analysis associations between MYO1H (P <0.001) and GHR (rs2973015 A>G) (P = 0.001) with PC2 and between FGF10 (rs593307 A<G) (P = 0.001) with PC4.

CONCLUSIONS

Polymorphism in MYO1H could be used as a marker for genetic susceptibility to Class III malocclusion with mandibular prognathism, and polymorphisms in GHR and FGF were associated with maxillomandibular discrepancies. This study may contribute to improved diagnosis and further research assessing possible differences in treatment responses based on genetic polymorphisms.

Review of the Genetic Basis of Jaw Malformations

Genetic etiologies for congenital anomalies of the facial skeleton, namely, the maxilla and mandible, are important to understand and recognize. Malocclusions occur when there exist any significant deviation from what is considered a normal relationship between the upper jaw (maxilla) and the lower jaw (mandible). They may be the result of anomalies of the teeth alone, the bones alone, or both. A number of genes play a role in the facial skeletal development and are regulated by a host of additional regulatory molecules. As such, numerous craniofacial syndromes specifically affect the development of the jaws. The following review discusses several genetic anomalies that specifically affect the bones of the craniofacial skeleton and lead to malocclusion.

An interview with Sylvia Frazier-Bowers

Dr. Frazier-Bowers is an associate professor at the University of North Carolina, Chapel Hill (UNC-CH), in the Department of Orthodontics. She received a BA from the University of Illinois, Urbana-Champaign, and a DDS from the University of Illinois, Chicago. After completing the NIH Dentist-Scientist Program at UNC-CH in Orthodontics (Certificate, 97’) and Genetics and Molecular Biology (PhD, 99’), she completed a post-doctoral fellowship at the University of Texas Health Science Center, Houston (UTHSC), in the Department of Orthodontics. Leadership positions include president of local NC-AADR (North Carolina (2005-2006); director of the AADR Craniofacial Biology group (CBG) 2004-2007; IADR/AADR councilor for NC-AADR (2007, 2008, 2012) and for the CBG (2012-2015); member of Southern Association of Orthodontists Scientific Affairs Committee (2005-2013) and the American Association of Orthodontists Council on Scientific Affairs (2014 – Present). Dr. Frazier-Bowers also serves various editorial boards including the Journal of Dental Research and the Scientific Advisory board for the Consortium on Orthodontic Advances in Science and Technology. Her current role as faculty at UNC-CH includes conducting human genetic studies to determine the etiology of inherited tooth disorders, mentoring students at all levels, teaching graduate and pre-doctoral level Growth and Development courses and treating patients in the UNC School of Dentistry faculty practice in Orthodontics.

Genetics of the dentofacial variation in human malocclusion

Malocclusions affect individuals worldwide, resulting in compromised function and esthetics. Understanding the etiological factors contributing to the variation in dentofacial morphology associated with malocclusions is the key to develop novel treatment approaches. Advances in dentofacial phenotyping, which is the comprehensive characterization of hard and soft tissue variation in the craniofacial complex, together with the acquisition of large-scale genomic data have started to unravel genetic mechanisms underlying facial variation. Knowledge on the genetics of human malocclusion is limited even though results attained thus far are encouraging, with promising opportunities for future research. This review summarizes the most common dentofacial variations associated with malocclusions and reviews the current knowledge of the roles of genes in the development of malocclusions. Lastly, this review will describe ways to advance malocclusion research, following examples from the expanding fields of phenomics and genomic medicine, which aim to better patient outcomes.

Whole-exome sequencing identifies a potential TTN mutation in a multiplex family with inguinal hernia

Purpose

Inguinal hernia repair is one of the most common procedures in general surgery. Males are seven times more likely than females to develop a hernia and have a 27 % lifetime ‘risk’ of inguinal hernia repair. Several studies have demonstrated that a positive family history is an important risk factor for the development of primary inguinal hernia, which indicates that genetic factors may play important roles in the etiology of the disease. So far, the contribution of genetic factors and underlying mechanisms for inguinal hernia remain largely unknown. The aim of this study was to investigate a multiplex Estonian family with inguinal hernia across four generations.

Methods

The whole-exome sequencing was carried out in three affected family members and subsequent mutation screening using Sanger sequencing was performed in ten family members (six affected and four unaffected).

Results

Whole-exome sequencing in three affected family members revealed a heterozygous missense mutation c.88880A>C (p.Lys29627Thr; RefSeq NM_001256850.1) in the highly conserved myosin-binding A-band of the TTN gene. Sanger sequencing demonstrated that this mutation cosegregated with the disease in this family and was not present in ethnically matched control subjects.

Conclusion

We report that missense variant in the A-band of TTN is the strongest candidate mutation for autosomal-dominant inguinal hernia with incomplete penetrance.

Electronic supplementary material

The online version of this article (doi:10.1007/s10029-016-1491-9) contains supplementary material, which is available to authorized users.

Identification of a Mutation in FGF23 Involved in Mandibular Prognathism

Mandibular prognathism (MP) is a severe maxillofacial disorder with undetermined genetic background. We collected a Chinese pedigree with MP which involved in 23 living members of 4 generations. Genome-wide linkage analysis were carried out to obtain the information in this family and a new MP-susceptibility locus, 12pter-p12.3 was identified. Whole-exome sequencing identified a novel heterozygous mutation in fibroblast growth factor (FGF) 23 (; p.A12D) which well segregated with MP in this pedigree within the locus. The mutation was also detected in 3 cases out of 65 sporadic MP patients, but not in any of the 342 control subjects. The p.A12D mutation may disrupt signal peptide function and inhibit secretory in FGF23. Furthermore, mutant FGF23 was overexpressed in 293T cells, increased cytoplasmic accumulation was observed compared with the wild type. We have discovered that c.35C>A mutation in FGF23 strongly associated with MP, which expand our understanding of the genetic contribution to MP pathogenesis.

Candidate Gene Analyses of Skeletal Variation in Malocclusion

This study evaluated associations between craniofacial candidate genes and skeletal variation in patients with malocclusion. Lateral cephalometric radiographs of 269 untreated adults with skeletal classes I, II, and III malocclusion were digitized with 14 landmarks. Two-dimensional coordinates were analyzed using Procrustes fit and principal component (PC) analysis to generate continuous malocclusion phenotypes. Skeletal class classifications (I, II, or III) were used as a categorical phenotype. Individuals were genotyped for 198 single-nucleotide polymorphisms (SNPs) in 71 craniofacial genes and loci. Phenotype-genotype associations were tested via multivariate linear regression for continuous phenotypes and multinomial logistic regression for skeletal malocclusion class. PC analysis resulted in 4 principal components (PCs) explaining 69% of the total skeletal facial variation. PC1 explained 32.7% of the variation and depicted vertical discrepancies ranging from skeletal deep to open bites. PC1 was associated with a SNP near PAX5 (P = 0.01). PC2 explained 21.7% and captured horizontal maxillomandibular discrepancies. PC2 was associated with SNPs upstream of SNAI3 (P = 0.0002) and MYO1H (P = 0.006). PC3 explained 8.2% and captured variation in ramus height, body length, and anterior cranial base orientation. PC3 was associated with TWIST1 (P = 0.000076). Finally, PC4 explained 6.6% and detected variation in condylar inclination as well as symphysis projection. PC4 was associated with PAX7 (P = 0.007). Furthermore, skeletal class II risk increased relative to class I with the minor alleles of SNPs in FGFR2 (odds ratio [OR] = 2.1, P = 0.004) and declined with SNPs in EDN1 (OR = 0.5, P = 0.007). Conversely, skeletal class III risk increased versus class I with SNPs in FGFR2 (OR 2.2, P = 0.005) and COL1A1 (OR = 2.1, P = 0.008) and declined with SNPs in TBX5 (OR = 0.5, P = 0.014). PAX5, SNAI3, MYO1H, TWIST1, and PAX7 are associated with craniofacial skeletal variation among patients with malocclusion, while FGFR2, EDN1, TBX5, and COL1A1 are associated with type of skeletal malocclusion.

Genetic association of ARHGAP21 gene variant with mandibular prognathism

Mandibular prognathism (MP) is a recognizable phenotype associated with dentoskeletal class III malocclusion. MP is a complex genetic trait, although familial recurrence also suggests the contribution of single inherited variations. To date, the genetic causes of MP have been investigated using linkage analysis or association studies in pooled families. Here for the first time, next-generation sequencing was used to study a single family with a large number of MP-affected members and to identify MP-related candidate genes. A 6-generation kindred with MP segregating as an autosomal dominant character was recruited. To identify family members affected by MP, a standard cephalometric procedure was used. In 5 MP subjects separated by the largest number of meioses, whole-exome sequencing was performed. Five promising missense gene variants (BMP3, ANXA2, FLNB, HOXA2, and ARHGAP21) associated with MP were selected and genotyped in most other family members. In this family, MP seemed to consist of 2 distinct genetic branches. Interestingly, the Gly1121Ser variant in the ARHGAP21 gene was found to be shared by all MP individuals in the larger branch of the family with nearly complete penetrance. This variant is rare in the Caucasian population (frequency 0.00034) and is predicted as damaging by all bioinformatic algorithms. ARHGAP21 protein strengthens cell-cell adhesions and may be regulated by bone morphogenetic factors, thus influencing mandibular growth. Further studies in both animal models and human patients are required to clarify the significance of this association.