Prevalence of Malocclusion Traits in Primary Dentition, 2010-2024: A Systematic Review

The present review was aimed to describe the prevalence and the regional distribution of malocclusion among preschool children worldwide. Two independent reviewers performed a systematic literature search to identify English publications from January 2010 to May 2024 using PubMed, ISI Web of Science and Embase. Search MeSH key words were "malocclusion", "primary dentition" and "child, preschool". The reporting quality was assessed by the modified Newcastle-Ottawa Quality Assessment Scale. We identified 2599 publications and recruited 47 articles. Fourteen of the included studies were conducted in Asia, four in Europe, twenty-eight in South America and one in Africa. The prevalence of malocclusion ranged from 28.4% to 83.9%, and half of the reported prevalences were higher than 50%. The highest percentage was in Asia (61.81%), followed by Europe (61.50%), South America (52.69%) and Africa (32.50%). Statistically significant differences existed in deep overbite, anterior open bite, posterior crossbite, edge-to-edge incisor relationship and distal step between continents (p < 0.05). Europe showed the highest prevalence (33.08%) of deep overbite. Africa showed the highest prevalence (18.60%) of anterior open bite. Europe showed the highest prevalence (15.38%) of posterior crossbite. The most common malocclusion traits were increased overjet and deep overbite. To conclude, malocclusion remained prevalent in the primary dentition and varied between countries.

Presence of single nucleotide polymorphisms in transforming growth factor β and insulin-like growth factor 1 in class II malocclusions due to retrognathic mandible

AIM

The aim of this study was to evaluate specific single nucleotide polymorphisms (SNP) of transforming growth factor-beta (TGF-β) (rs1800469) and insulin-like growth factor-1 (IGF-1) (rs17032362) genes in Class II individuals with a normal maxilla and retrognathic (short) mandible.

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.

Genetics of three-dimensional tooth inclination and angulation in orthodontic patients with Class I Occlusion: A cross-sectional study

PURPOSE

This cross-sectional study aimed to utilize quantitative polymerase chain reaction (qPCR) to investigate the influence of genetic variance over teeth inclination and angulation in orthodontic patients with Class I occlusion.

MATERIALS AND METHODS

DNA was extracted from adolescent patients seeking orthodontic treatment in a single institution (from July 2018 to April 2020), who had CBCTs taken as part of initial standardized records. Patients had permanent dentition, Class I skeletal and dental classifications, with normal vertical and transverse skeletal dimensions, normal incisors inclination, no to mild crowding or spacing. qPCR was performed using genetic markers for candidate genes EPB41, TGFβ3, GHR and PAX9. Three-dimensional teeth inclinations (TI) and angulations (TA) were evaluated using Invivo6 software and correlated with genotypes. Reliability of TI and TA was assessed using intraclass correlation coefficients (ICC). Mixed models and multiple linear regression analyses were used to assess the association between each single nucleotide polymorphisms (SNP) with tooth inclination (TI) and with tooth angulation (TA). The results were evaluated at the significance level of P<0.05.

RESULTS

Twenty four adolescent patients with mean age of 13.4±2.4 years were included in the study. ICC showed adequate intra-examiner reliability for TI and TA (0.806<r<0.988, P<0.001). Multiple linear regression analysis showed a significant association between TI and homozygous-T polymorphism for PAX9 (P=0.028) and homozygous-G polymorphism for GHR (P=0.028). Also, a significant association between TA and homozygous-A polymorphism for EPB41 (P=0.019) and homozygous-G polymorphism for GHR (P=0.001) was evident.

CONCLUSIONS

Autosomal recessive patterns of inheritance for PAX9 and GHR with TI and for EPB41 and GHR with TA were shown. This study offers insight toward the hierarchical nature of epigenetic interactions between heredity and the environment in determining the three-dimensional positions of teeth in orthodontic patients with Class I occlusion.

Dissecting the Complexity of Skeletal-Malocclusion-Associated Phenotypes: Mouse for the Rescue

Skeletal deformities and malocclusions being heterogeneous traits, affect populations worldwide, resulting in compromised esthetics and function and reduced quality of life. Skeletal Class III prevalence is the least common of all angle malocclusion classes, with a frequency of 7.2%, while Class II prevalence is approximately 27% on average, varying in different countries and between ethnic groups. Orthodontic malocclusions and skeletal deformities have multiple etiologies, often affected and underlined by environmental, genetic and social aspects. Here, we have conducted a comprehensive search throughout the published data until the time of writing this review for already reported quantitative trait loci (QTL) and genes associated with the development of skeletal deformation-associated phenotypes in different mouse models. Our search has found 72 significant QTL associated with the size of the mandible, the character, shape, centroid size and facial shape in mouse models. We propose that using the collaborative cross (CC), a highly diverse mouse reference genetic population, may offer a novel venue for identifying genetic factors as a cause for skeletal deformations, which may help to better understand Class III malocclusion-associated phenotype development in mice, which can be subsequently translated to humans. We suggest that by performing a genome-wide association study (GWAS), an epigenetics-wide association study (EWAS), RNAseq analysis, integrating GWAS and expression quantitative trait loci (eQTL), micro and small RNA, and long noncoding RNA analysis in tissues associated with skeletal deformation and Class III malocclusion characterization/phenotypes, including mandibular basic bone, gum, and jaw, in the CC mouse population, we expect to better identify genetic factors and better understand the development of this disease.

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.

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.

Comparison of stress distribution of TMJ with different mandibular deformities under incisal clenching

Temporomandibular joint (TMJ) is an important and complex joint in the human body. It is necessary to explore the biomechanical influence on the TMJs caused by different mandibular deformities. The maxillofacial models from 34 subjects were built to analyze the maximum and minimum principal stresses of the TMJs in the control group and three test groups. The results showed that only the deviation group had statistical differences between both sides. And these mandibular deformities decreased the tensile stresses of the temporal bones and increased the compressive stresses of the condyles and the discs. The patients with mandibular deviation had most risk with TMD.

Targeted sequencing of NOTCH signaling pathway genes and association analysis of variants correlated with mandibular prognathism

Introduction

The purpose of this study was to systematically identify variants in NOTCH signaling pathway genes that correlate with mandibular prognathism (MP) in the general Chinese population.

Methods

Targeted sequencing of NOTCH signaling pathway genes was conducted in 199 MP individuals and 197 class I malocclusion control individuals. The associations of common and rare variants with MP, cephalometric parameters, and continuous cephalometric phenotypes were analyzed by principal component (PC) analysis. The associations between rare variants and MP were tested for each gene.

Results

Six SNPs, including rs415929, rs520688, and rs423023 in an exonic region of NOTCH4; rs1044006 in an exonic region of NOTCH3; rs1051415 in an exonic region of JAG1; and rs75236173 in the 3′-untranslated region (3′-UTR) of NUMB were associated with MP (P < 0.05). One common variant, rs1051415, in an exonic region of JAG1 was significantly related to PC1 (P  = 3.608 × 10^− 4), which explained 24.3% of the overall phenotypic variation observed and corresponded to the sagittal mandibular position towards the maxilla, ranging from a posterior positioned mandible to an anterior positioned mandible. Additionally, 41 other variants were associated with PC1–5 (P  <  0.05). With respect to rare variant analysis, variants within the EP300, NCOR2, and PSEN2 gene showed an association with MP (t   < 0 .05).

Conclusions

An association between NOTCH signaling pathway genes and MP has been identified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13005-021-00268-0.

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.

Association Between Mandibular Prognathism and MATRILIN-1 Gene in Central India Population: A Cross-sectional Study

Introduction:

Mandibular prognathism (MP) is known to be an inherited trait. Secondary condylar cartilage is the postnatal growth site of the mandible. Chromosome location 1p36 contains MATRILIN-1, which is related to cartilage matrix formation. The aim of this article is to find out relation between mutation in gene encoding MATRILIN-1 at 1p36 and MP.

Material and Methods:

This case control study included 35 skeletal class III patients with MP (18 males and 17 females in the age range from 6 years to 63 years; mean age was 21.74 ± 12.87 years) and 30 control individuals with orthognathic skeletal relation (17 males, 13 females in the age range from 19 years to 25 years, mean age of 21.57 ± 2.59 years) without any family history of MP. DNA was extracted from venous blood and genotyped. Two loci on chromosome 1p36 (rs20566 and rs1065755) encoding MATRILIN-1 were studied for mutation.

Results:

Single-nucleotide polymorphism (SNP) at rs20566 and frameshift mutation at rs1065755 had a significantly greater frequency in MP cases than in control.

Conclusions:

Mutation at both the sites can be attributed to increased risk of developing MP.

Different approaches for management of Class III siblings: A long-term follow-up of two case reports

Class III malocclusion can be varied in presentation and progression. This report describes the presentation, course of treatment and long-term follow-up of two siblings with Class III malocclusion. Two cases discussed in this report were different in their presentation. Sibling 1, a 19-year-old male patient had developed skeletal Class III malocclusion with severe maxillomandibular discrepancy, showing both components of maxillary hypoplasia and mandibular prognathism & asymmetry with average growth pattern. Sibling 2, a 13-year-old male patient had developed a Class III malocclusion with maxillary retrognathism with vertical growth pattern. An insight into the similarities and dissimilarities in the presentation, course of treatment and long-term follow-up of the two cases is provided. The two cases were successfully managed with entirely different treatment approaches. Sibling 1 underwent maxillary advancement with Le Fort I surgery and mandibular set back and rotation with bilateral sagittal split osteotomy which was preceded by pre-surgical orthodontic treatment with extraction of upper first premolars for orthodontic decompensation. Sibling 2 was treated with skeletally anchored facemask therapy followed by fixed mechanotherapy. Acceptable clinical outcome with long-term stability of the treatment results was observed in the two siblings. Orthognathic surgery may be completely avoided later if early orthopaedic treatment to advance the maxilla is initiated at an appropriate age.

Review of Etiology of Posterior Open Bite: Is There a Possible Genetic Cause?

Posterior open bite (POB) is one of the most severe malocclusions that can impair patients' masticatory functions, yet it is also a condition that is poorly understood and not well studied. Most reported cases are either sporadic or idiosyncratic with a diverse yet poorly understood etiology. Although primary failure of eruption (PFE), lateral tongue thrust, and certain medical syndromes or pathology of the temporomandibular joints have all been shown to cause POB, the complex interplay of environmental and genetic factors makes its etiopathogenesis a difficult subject to understand and investigate. Here, we provide a comprehensive review of the etiology of posterior open bite. Additionally, a genetic cause for POB is proposed through a report of an apparently non-syndromic familial case series with high POB penetrance across two generations. Further investigations of the gene(s) and mechanism(s) involved can not only provide a unique opportunity to better understand POB and the intricate muscular-occlusal relationship, but also offer powerful insight into the most effective approaches to clinical management of these (and potentially other) malocclusions.

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.

Orthodontics and Genetics

Introduction:

Genetics has been suggested as an explanation for the etiology of malocclusions, although some questions, due to the perception that genetic inheritance is tied to a monogenic or Mendelian form of inheritance.

Objective:

This paper describes the inheritance of malocclusions, highlighting the areas of knowledge where research has explored mechanisms that explain deviations in patterns of craniofacial growth.

Conclusion:

Malocclusions have a complex or multifactorial pattern of inheritance, where more than one gene is involved in the development of the phenotype. There is also the possibility that the environment influences malocclusions.

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.

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.

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.

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.

Classification and characterization of class III malocclusion in Chinese individuals

BACKGROUND

Class III malocclusion is a maxillofacial disorder that is characterised by a concave profile and can be attributed to both genetic inheritance and environmental factors. It is a clinical challenge due to our limited understanding of its aetiology. Revealing its prototypical diversity will contribute to our sequential exploration of the underlying aetiological information. The objective of this study was to characterize phenotypic variations of Class III malocclusion via a lateral cephalometric analysis in a community of Chinese individuals.

METHOD

One-hundred-and-forty-four individuals (58 males ≥18 and 86 females ≥16) with Class III malocclusion ranging from mild to severe were enrolled in this study. Principal component analysis and cluster analysis were performed using 61 lateral cephalometric measurements.

RESULTS

Six principal components were discovered in the examined population and were responsible for 73.7 % of the variability. Four subtypes were revealed by cluster analysis. Subtype 1 included subjects with mild mandibular prognathism with a steep mandibular plane. Subjects in subtype 2 showed a combination of prognathic mandibular and retrusive maxillary with a flat or normal mandibular plane. Subtype 3 included individuals with purely severe mandibular prognathism and a normal mandibular plane. Individuals in subtype 4 had a mild maxillary deficiency and severe mandibular prognathism with the lowest mandibular plane angle.

CONCLUSION

The six principal components extracted among the 61 variables improve our knowledge of lateral cephalometric analysis for diagnoses. We successfully identified four Class III malocclusion subtypes, indicating that cluster analysis could supplement the classification of Class III malocclusion among a Chinese population and may assist in our on-going genetic study.

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.

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.

The ADAMTS1 Gene Is Associated with Familial Mandibular Prognathism

Mandibular prognathism is a facial skeletal malocclusion. Until now, the genetic mechanism has been unclear. The goal of this study was to identify candidate genes or genomic regions directly associated with mandibular prognathism development, by employing whole genome sequencing. A large Chinese family was recruited, composed of 9 affected and 12 unaffected individuals, and the inheritance pattern of this family tends to be autosomal dominant. A single-nucleotide missense mutation in the ADAMTS1 gene (c. 742I>T) was found to segregate in the family, given that the affected individuals must be heterozygous for the mutation. For mutation validation, we screened this candidate mutation and 15 tag single-nucleotide polymorphisms in the coding sequence of ADAMTS1 among 230 unrelated cases and 196 unrelated controls using Sequenom Massarray and found that 3 in 230 cases carried this mutation and none of the controls did. Final results suggested that 2 single-nucleotide polymorphisms (rs2738, rs229038) of ADAMTS1 were significantly associated with mandibular prognathism.

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.

Relationship between P561T and C422F polymorphisms in growth hormone receptor gene and mandibular prognathism

OBJECTIVE

To evaluate the allele and genotype frequencies of the P561T and C422F polymorphic sites of the growth hormone receptor (GHR) gene and the relationship between mandibular prognathism (MP) and these two single-nucleotide polymorphisms (SNPs).

MATERIALS AND METHODS

A total of 99 subjects with severe skeletal Class III MP who planned to undergo orthognathic surgery and 99 subjects with Class I occlusion were examined in this study to evaluate the relationship between MP and two SNPs in exon 10 of the GHR gene. GHR was chosen as a candidate gene because growth hormone plays an important role in cartilage growth. A blood sample was used to extract genomic DNA, and the polymerase chain reaction-restriction fragment length polymorphism method was used to determine genotypes of P561T and C422F. The Minitab 14.0 packet program was used to perform statistical analysis.

RESULTS

Allele frequencies of the C422F and P561T variants were determined. Because of the low allele frequency of the control group, statistical analysis could not be performed to test the difference between MP and control groups. Therefore, the data were combined to determine the association between the P561T polymorphism and craniofacial measurements. Effective mandibular length (condylion-gnathion) and lower face height (anterior nasal spina-menton) were associated with the P561T variant.

CONCLUSION

This finding supports that the GHR might be a candidate gene for mandibular morphogenesis in this population.

Microsatellite genome-wide association study for mandibular prognathism

INTRODUCTION

Attempts have been made to identify susceptibility genes of mandibular prognathism by genome-wide linkage studies, but the results of susceptibility loci are inconsistent. There has been no genome-wide association study of mandibular prognathism. Our objective was to perform a genome-wide association study using 23,465 microsatellite markers to detect mandibular prognathism susceptibility regions.

METHODS

The study was based on the pooled DNA method, including 2 steps of screening on the whole genome and subsequent individual genotyping, with 240 experimental subjects and 360 control subjects from the Japanese population.

RESULTS

Two suggestive associations on chromosomes 1q32.2 (D1S1358i: P = 4.22 × 10(-4)) and 1p22.3 (D1S0411i: P = 6.66 × 10(-4)) were shown, and PLXNA2 and SSX2IP were suggested to be candidate genes; 1p22.3 flanked the region indicated by previous linkage analysis.

CONCLUSIONS

The results of the genome-wide association study showed that 2 loci (1q32.2 and 1p22.3) are likely to be susceptibility regions of mandibular prognathism: 1p32.2 is a novel locus, and identification of 1p22.3 supports the results of previous linkage analysis.

Phenotypic diversity in white adults with moderate to severe Class II malocclusion

INTRODUCTION

Class II malocclusion affects about 15% of the population in the United States and is characterized by a convex profile and occlusal disharmonies. The specific etiologic mechanisms resulting in the range of Class II dentoskeletal combinations observed are not yet understood. Most studies describing Class II phenotypic diversity have used moderate sample sizes or focused on younger patients who later in life might outgrow their Class II discrepancies; such a focus might also preclude the visualization of adult Class II features. The majority have used simple correlation methods resulting in phenotypes that might not be generalizable to different samples and thus might not be suitable for studies of malocclusion etiology. The purpose of this study was to address these knowledge gaps by capturing the maximum phenotypic variations in a large sample of white Class II subjects selected with strict eligibility criteria and rigorously standardized multivariate reduction analyses.

METHODS

Sixty-three lateral cephalometric variables were measured from the pretreatment records of 309 white Class II adults (82 male, 227 female; ages, 16-60 years). Principal component analysis and cluster analysis were used to generate comprehensive phenotypes to identify the most homogeneous groups of subjects, reducing heterogeneity and improving the power of future malocclusion etiology studies.

RESULTS

Principal component analysis resulted in 7 principal components that accounted for 81% of the variation. The first 3 components represented variation on mandibular rotation, maxillary incisor angulation, and mandibular length. The cluster analysis identified 5 distinct Class II phenotypes.

CONCLUSIONS

A comprehensive spectrum of Class II phenotypic definitions was obtained that can be generalized to other samples to advance our efforts for identifying the etiologic factors underlying Class II malocclusion.

The role of polymorphisms associated with early tooth eruption in dental and occlusal traits in East Asian populations

OBJECTIVE

A recent study suggested that rs6504340, a polymorphism within the homeobox B (HOXB) gene cluster, is associated with the susceptibility for malocclusions in Europeans. The resulting malocclusions require orthodontic treatment. The aim of this study was to investigate the association of rs6504340 and other dentition-implicated polymorphisms with dental and occlusal traits in Korean and Japanese populations.

METHODS

The study participants included 223 unrelated Koreans from the Busan area and 256 unrelated Japanese individuals from the Tokyo metropolitan area. DNA samples were extracted from saliva specimens. Genotyping for rs6504340 and four single nucleotide polymorphisms (SNPs) that have been shown to be associated with the timing of first tooth eruption and the number of teeth at 1 year of age (rs10506525, rs1956529, rs9674544, and rs8079702) was performed using TaqMan assays. The Index of Orthodontic Treatment Need (IOTN), overjet, overbite, arch length discrepancy, crown sizes, and length and width of the dental arches were measured. Spearman's correlation coefficients were calculated to evaluate relationships between rs6504340 and these dental/occlusal traits.

RESULTS

We evaluated the aesthetic components and dental health components of the IOTN in the Korean and Japanese populations and found that neither rs6504340 nor the other four SNPs showed any association with dental and occlusal traits in these East Asian populations.

CONCLUSIONS

These negative results suggest that further research is needed to identify the genetic determinants of malocclusions in order to reach a consensus.

A chromosomal region on ECA13 is associated with maxillary prognathism in horses

Hereditary variations in head morphology and head malformations are known in many species. The most common variation encountered in horses is maxillary prognathism. Prognathism and brachygnathism are syndromes of the upper and lower jaw, respectively. The resulting malocclusion can negatively affect teeth wear, and is considered a non-desirable trait in breeding programs. We performed a case-control analysis for maxillary prognathism in horses using 96 cases and 763 controls. All horses had been previously genotyped with a commercially available 50 k SNP array. We analyzed the data with a mixed-model considering the genomic relationships in order to account for population stratification. Two SNPs within a region on the distal end of chromosome ECA 13 reached the Bonferroni corrected genome-wide significance level. There is no known prognathism candidate gene located within this region. Therefore, our findings in the horse offer the possibility of identifying a novel gene involved in the complex genetics of prognathism that might also be relevant for humans and other livestock species.

Phenotypic diversity in white adults with moderate to severe Class III malocclusion

INTRODUCTION

Class III malocclusion is characterized by a composite of dentoskeletal patterns that lead to the forward positioning of the mandibular teeth in relation to the maxillary teeth and a concave profile. Environmental and genetic factors are associated with this condition, which affects 1% of the population in the United States and imposes significant esthetic and functional burdens on affected persons. The purpose of this study was to capture the phenotypic variation in a large sample of white adults with Class III malocclusion using multivariate reduction methods.

METHODS

Sixty-three lateral cephalometric variables were measured from the pretreatment records of 292 white subjects with Class II malocclusion (126 male, 166 female; ages, 16-57 years). Principal component analysis and cluster analysis were used to capture the phenotypic variation and identify the most homogeneous groups of subjects to reduce genetic heterogeneity.

RESULTS

Principal component analysis resulted in 6 principal components that accounted for 81.2% of the variation. The first 3 components represented variation in mandibular horizontal and vertical positions, maxillary horizontal position, and mandibular incisor angulation. The cluster model identified 5 distinct subphenotypes of Class III malocclusion.

CONCLUSIONS

A spectrum of phenotypic definitions was obtained replicating results of previous studies and supporting the validity of these phenotypic measures in future research of the genetic and environmental etiologies of Class III malocclusion.

A missense mutation in DUSP6 is associated with Class III malocclusion

Class III malocclusion is a common dentofacial phenotype with a variable prevalence according to ethnic background. The etiology of Class III malocclusion has been attributed mainly to interactions between susceptibility genes and environmental factors during the morphogenesis of the mandible and maxilla. Class III malocclusion shows familial recurrence, and family-based studies support a predominance of an autosomal-dominant mode of inheritance. We performed whole-exome sequencing on five siblings from an Estonian family affected by Class III malocclusion. We identified a rare heterozygous missense mutation, c.545C>T (p.Ser182Phe), in the DUSP6 gene, a likely causal variant. This variant co-segregated with the disease following an autosomal-dominant mode of inheritance with incomplete penetrance. Transcriptional activation of DUSP6 has been presumed to be regulated by FGF/FGFR and MAPK/ERK signaling during fundamental processes at early stages of skeletal development. Several candidate genes within a linkage region on chromosome 12q22-q23--harboring DUSP6--are implicated in the regulation of maxillary or mandibular growth. The current study reinforces that the 12q22-q23 region is biologically relevant to craniofacial development and may be genetically linked to the Class III malocclusion.

Segregation analysis of mandibular prognathism in Korean orthognathic surgery patients and their families

Objective:

To investigate the existence of genetic influences on the incidence of mandibular prognathism (MP) in Korean Class III patients.

Materials and Methods:

The probands consisted of 100 Class III patients with MP (51 men and 49 women; mean age, 22.1 ± 5.2 years; SNA, 81.2° ± 3.2°; SNB, 84.1° ± 3.9°) who underwent orthognathic surgery. Using three-generation pedigree charts, questionnaires, and clinical examinations, general information and information regarding MP for a total of 3777 relatives of the probands (1911 men and 1866 women) was ascertained. Familial correlations of MP between possible pairs in the pedigree were estimated. Heritability (h2) of MP under various models was estimated. Segregation analysis was conducted under the assumption of the nonpolygenic multivariate logistic model and finite polygenic mixed model. One-, two-, and three-susceptibility-type models were evaluated.

Results:

Among 3777 relatives, 199 (97 men and 102 women) were affected with MP (5.3%). Correlation coefficients of MP incidence in full siblings and in parent-offspring were .2003 and .2036, respectively (all P &lt; .001). The h2 of MP was estimated as 21.5% after adjusting for sex and founder effects. Two- and three–susceptibility-type models showed that the general model fit better than the other models. MP incidence did not have a major gene transmission model and was influenced by numerous minor effect genes and their additive effects.

Conclusion:

These results suggest that the inherited susceptibility to MP in Korean Class III patients might be due to the summation of minor effects from a variety of different genes and/or influence of environmental factors, rather than Mendelian transmission of major genes.

Association between CYP19A1 genotype and pubertal sagittal jaw growth

INTRODUCTION

Sagittal jaw growth is influenced during puberty by a ratio of androgens and estrogens. The CYP19A1 (formerly CYP19) gene encodes the cytochrome P450 enzyme aromatase (estrogen synthetase), which converts testosterone to estrogen. Genetic variations including single nucleotide polymorphisms might regulate CYP19A1 gene expression or the function of the aromatase protein and thus influence sagittal jaw growth.

METHODS

The annual sagittal jaw growth in 92 pubertal orthodontic patients was determined by using pretreatment and posttreatment cephalometric radiographs. Single nucleotide polymorphisms rs2470144 and rs2445761 were genotyped and haplotypes constructed. Associations between genotypes or haplotypes and the annual sagittal growth were estimated by using JMP (version 9.0; SAS Institute, Cary, NC).

RESULTS

Two single nucleotide polymorphisms were significantly associated with average differences in annual sagittal jaw growth in boys. Haplotype analysis demonstrated that haplotypes T(rs2470144)T(rs2445761) and C(rs2470144)T(rs2445761) had significant effects on annual sagittal maxillary growth and on mandibular growth in boys. No association was found in girls.

CONCLUSIONS

A quantitative trait locus that influences male pubertal sagittal jaw growth might exist in the CYP19A1 gene, and single nucleotide polymorphisms rs2470144 and rs2445761 might be inside this quantitative trait locus or be linked to it.

Genetic variation in myosin 1H contributes to mandibular prognathism

INTRODUCTION

Several candidate loci have been suggested as influencing mandibular prognathism (1p22.1, 1p22.2, 1p36, 3q26.2, 5p13-p12, 6q25, 11q22.2-q22.3, 12q23, 12q13.13, and 19p13.2). The goal of this study was to replicate these results in a well-characterized homogeneous sample set.

METHODS

Thirty-three single nucleotide polymorphisms spanning all candidate regions were studied in 44 prognathic and 35 Class I subjects from the University of Pittsburgh School of Dental Medicine Dental Registry and DNA Repository. The 44 subjects with mandibular prognathism had an average age of 18.4 years; 31 were female and 13 male; and 24 were white, 15 African American, 2 Hispanic, and 3 Asian. The 36 Class I subjects had an average age of 17.6 years; 27 were female and 9 male; and 27 were white, 6 African American, 1 Hispanic, and 2 Asian. Skeletal mandibular prognathism diagnosis included cephalometric values indicative of Class III such as an ANB smaller than 2°, a negative Wits appraisal, and a positive A-B plane. Additional mandibular prognathism criteria included negative overjet and visually prognathic (concave) profile as determined by the subject's clinical evaluation. Orthognathic subjects without jaw deformations were used as the comparison group. The mandibular prognathic and orthognathic subjects were matched by race, sex, and age. Genetic markers were tested by polymerase chain reaction with TaqMan chemistry. Chi-square and Fisher exact tests were used to determine overrepresentation of marker allele with an alpha of 0.05.

RESULTS

An association was unveiled between a marker in MYO1H (rs10850110) and the mandibular prognathism phenotype (P = 0.03). MYO1H is a Class I myosin that is in a different protein group than the myosin isoforms of muscle sarcomeres, which are the basis of skeletal muscle fiber typing. Class I myosins are necessary for cell motility, phagocytosis, and vesicle transport.

CONCLUSIONS

More strict clinical definitions might increase homogeneity and aid the studies of genetic susceptibility to malocclusions. We provide evidence that MYO1H can contribute to mandibular prognathism.