From a morphological perspective, a Class III skeletal pattern can be associated with maxillary deficiency, mandibular prognathism (MP) or a combination of both conditions.1,2 The roles and contribution of the maxilla and mandible in the development of a Class III skeletal pattern have been reported and many studies have observed maxillary retrognathism (MR) as frequently as MP.2–5 Genetics is a major determining factor in the aetiology of a Class III skeletal pattern, which invariably has a multifactorial aetiology.6 Genetic factors can cause over-development of the mandible or under-development of the maxilla and so may be involved in all combinations of a Class III skeletal pattern.1
Current management options range from orthopaedic treatment at an early developmental age to orthognathic surgery performed after dento-facial growth and development have been completed. In the future, the identification of candidate genes will enable the determination of individuals with a relatively high likelihood of developing a Class III skeletal pattern. This approach will allow early diagnosis, interceptive treatment and interventions targeting dento-facial anomalies.7
The
The
The present study was approved by the Ethics Committee of Ege University, School of Medicine (16-6/17). Based on the inclusion criteria, two hundred and fifty-five patients (85 with MP, 85 with MR and 85 control subjects) were selected from individuals who presented to the Orthodontic Department of Aydın Adnan Menderes University, Faculty of Dentistry between September 2017 and May 2018. All patients and legal guardians provided written informed consent before a lateral cephalometric radiograph and a blood sample were taken. A CONSORT diagram showing the patient flow throughout the study is shown in Figure 1. No patients nor samples were lost during the study.
The skeletal malocclusions were identified using the SNA, SNB and ANB angles, plus the Wits value. Patients with an ANB angle <0° and a Wits value of <0 mm were considered to have a Class III skeletal pattern. The study group included patients with a Class III skeletal pattern due to two distinct aetiologies. The MR group (
Demographic characteristics of all patients.
Variable | Mandibular prognathism ( | Maxillary retrognathism ( | Control ( | |||||||
---|---|---|---|---|---|---|---|---|---|---|
Sex | Female | Male | Female | Male | Female | Male | ||||
(n = 49) | (n = 36) | (n = 53) | (n = 32) | (n = 52) | (n = 33) | |||||
Age (years) | 19.41 ± 8.26 | 18.27 ± 5.89 | 17.69 ± 2.06 | 0.165 | ||||||
17.73 ± 5.55 | 21.69 ± 10.6 | 17.62 ± 4.07 | 19.34 ± 8.02 | 17.69 ± 2.16 | 17.70 ± 1.92 | |||||
Height (cm) | 168.89 ± 8.74 | 167.78 ± 7.15 | 168.78 ± 7.15 | 0.585 | ||||||
165.51 ± 6.76 | 173.39 ± 9.18 | 165.49 ± 6.29 | 171.56 ± 6.95 | 165.85 ± 5.41 | 173.39 ± 7.19 | |||||
SNA | 82.18 ± 1.60 | 76.62 ± 1.66 | 81.85 ± 3.81 | 0.000*** | ||||||
82.04 ± 1.67 | 82.36 ± 1.51 | 76.62 ± 1.76 | 76.62 ± 1.49 | 82.08 ± 3.90 | 81.49 ± 3.70 | |||||
SNB | 85.42 ± 2.42 | 80.04 ± 1.31 | 79.84 ± 3.80 | 0.000*** | ||||||
84.98 ± 2.68 | 86.02 ± 2.43 | 79.88 ± 1.35 | 80.28 ± 1.22 | 78.79 ± 3.90 | 78.91 ± 3.69 | |||||
ANB | -3.35 ± 1.85 | -3.58 ± 1.48 | 2.91 ± 0.97 | 0.000*** | ||||||
-3.12 ± 1.55 | -3.66 ± 2.17 | -3.52 ± 1.40 | -3.65 ± 1.61 | 3.12 ± 1.10 | 2.58 ± 0.70 | |||||
Wits | -9.42 ± 3.12 | -9.16 ± 3.40 | 0.39 ± 0.62 | 0.000*** | ||||||
-8.65 ± 2.36 | -10.47 ± 3.69 | -8.94 ± 3.24 | -9.53 ± 3.67 | 0.35 ± 0.48 | 0.46 ± 0.79 |
***
Cephalometric analyses were performed for the 255 patients by a single researcher (B.T) using Dolphin Imaging 11.9 software (Dolphin Imaging and Management Solutions, Chatsworth, CA, USA). The linear cephalometric measurements used are shown in Figure 2. Thirty radiographs were randomly selected and cephalometric analyses were repeated 2 weeks later to determine intra-operator tracing errors. A paired
The SNPs were selected using the NCBI dbSNP databases and chosen on the basis of their minor allele frequency >10%. The characteristics of the studied SNPs are shown in Table II. The blood samples were drawn and stored at −80°C. When required for the genetic assays, the frozen samples were simultaneously thawed and assayed by DNA isolation, followed by PCR and pyro-sequencing conducted at the Molecular Biology Laboratory in the Pathology Department of Aydın Adnan Menderes University School of Medicine. Genomic DNA was extracted using the QIAamp DNA Blood Mini Kit (Qiagen GmbH, Hilden, Germany). For each DNA sample, three separate PCR reactions were performed using a SensoQuest LabCycler. The mixture of PCR reaction products was combined with the sequencing primers in each well of the Q24 plate (specific to the device) for pyro-sequencing. Sequences belonging to rs6182 and rs6184 loci of the
Characteristics of the SNPs studied.
Genes | SNP ID | Location | Type of alteration | Alleles | Global MAF |
---|---|---|---|---|---|
rs6182 | chr5:42718826 | missense variant | G > T | 0.07 | |
rs6184 | chr5:42719242 | missense variant | C > A | 0.07 | |
rs1793953 | chr12:47999743 | intron variant | C > T | 0.44 |
Note: Source of information: dbSNP from:
The normality of the data was tested using the histogram method, Q–Q plots and the Shapiro–Wilk test. Variance homogeneity was assessed using the Levene test. The Hardy–Weinberg Equilibrium (HWE) of the groups was controlled in relation to the genotypes. For intergroup comparisons, quantitative variables were evaluated by one-way analysis of variance (ANOVA) and the two-sample
Table III presents the results of the lateral cephalometric radiographs of patients in the three groups. A difference between the groups was anticipated because the skeletal measurements were used to define the groups.
Comparison of lateral cephalometric measurements between groups.
Group | ||||
---|---|---|---|---|
Mandibular Prognathism ( | Maxillary Retrognathism ( | Control ( | ||
82.18 ± 1.60a | 76.62 ± 1.66b | 81.85 ± 3.81a | 0.000*** | |
47.00 ± 4.21a | 44.51 ± 3.10b | 48.02 ± 3.50a | 0.000*** | |
76.01 ± 10.12b | 73.22 ± 4.48a | 77.09 ± 5.22b | 0.000*** | |
-0.67 ± 3.47a | -2.13 ± 2.91b | 0.53 ± 3.30c | 0.000*** | |
85.42 ± 2.42a | 80.04 ± 1.31b | 79.84 ± 3.80b | 0.000*** | |
45.46 ± 5.19a | 43.48 ± 4.07b | 43.85 ± 4.44b | 0.004** | |
72.55 ± 5.72a | 69.90 ± 7.94b | 70.51 ± 4.29b | 0.015*** | |
65.80 ± 7.60a | 63.49 ± 4.47b | 62.55 ± 4.11b | 0.000*** | |
110.87 ± 9.69a | 105.18 ± 6.30b | 105.79 ± 6.12b | 0.000*** | |
6.34 ± 6.65a | 2.07 ± 6.55b | -1.39 ± 6.15c | 0.000*** | |
-3.35 ± 1.85a | -3.58 ± 1.48a | 2.91 ± 0.97b | 0.000*** | |
-9.42 ± 3.12a | -9.16 ± 3.40a | 0.39 ± 0.62b | 0.000*** | |
35.84 ± 5.25a | 35.84 ± 4.78a | 28.34 ± 3.67b | 0.000*** | |
63.88 ± 4.08 | 63.91 ± 3.32 | 64.02 ± 3.76 | 0.132 | |
33.74 ± 4.45a | 31.45 ± 3.40b | 34.27 ± 3.67a | 0.000*** | |
42.11 ± 4.86a | 39.98 ± 3.75b | 41.61 ± 3.30a | 0.002** | |
61.81 ± 9.42 | 61.47 ± 5.98 | 59.81 ± 5.35 | 0.107 |
Notes: n: Sample size; **
All SNPs were consistent with HWE. Table IV shows the allele and genotype distribution of 3 SNPs. In the
Statistical analysis of alleles and genotypes of rs6182, rs6184 and rs1793953 loci and dominant and recessive model of rs1793953 loci.
Group | MP-Control | MR-Control | |||||
---|---|---|---|---|---|---|---|
Gene | Mandibular Prognathism ( | Maxillary Retrognathism ( | Control ( | ||||
| 165 (97.1) | 169 (99.4) | 169 (99.4) | 0.215 | 1.000 | ||
| 5 (2.9) | 1 (0.6) | 1 (0.6) | ||||
| 80 (94.1) | 84 (98.8) | 84 (98.8) | 0.210 | 1.000 | ||
| 5 (5.9) | 1 (1.2) | 1 (1.2) | ||||
| 166 (97.6) | 169 (99.4) | 169 (99.4) | 0.371 | 1.000 | ||
| 4 (2.4) | 1 (0.6) | 1 (0.6) | ||||
| 81 (95.3) | 84 (98.8) | 84 (98.8) | 0.368 | 1.000 | ||
| 4 (4.7) | 1 (1.2) | 1(1.2) | ||||
| 69 (40.6) | 73 (42.9) | 62(36.5) | 0.435 | 0.223 | ||
| 101 (59.4) | 97 (57.1) | 108(63.5) | ||||
| 11 (12.9) | 16 (18.8) | 14 (16.5) | 0.135 | 0.362 | ||
| 27 (31.8) | 28 (32.9) | 37 (43.5) | ||||
| 47 (55.3) | 41 (48.2) | 34 (40.0) | ||||
CC + CT | 58 (68.2) | 57 (67.1) | 48 (56.5) | 0.113 | 1.65(0.88 − 3.09) | 0.155 | 1.56(0.84 − 2.92) |
TT | 27 (31.8) | 28 (32.9) | 37 (43.5) | ||||
CC | 11 (12.9) | 16 (18.8) | 14 (16.5) | 0.665 | 0.75(0.32 − 1.77) | 0.841 | 1.17(0.53 − 2.59) |
CT + TT | 74 (87.1) | 69 (81.1) | 71 (83.5) |
Notes: Values are presented as number (%). n, sample size; MP, mandibular prognathism; MR, maxillary retrognathism; OR, odds ratio; CI, confidence interval.
Genetic models for the
Associations were detected when specific cephalometric measurements were assessed. In the statistical comparison between genotypes in SNP rs6182 using cephalometric measurements, the GT genotype correlated with ramus height (Ar–Go) in the total sample (
Association between rs6182 polymorphism and cephalometric values; rs6184 polymorphism and cephalometric values in the total sample.
rs6182 | |||
---|---|---|---|
GG ( | GT ( | ||
168.34 ± 7.68 | 173.14 ± 7.28 | 0.105 | |
43.99 ± 4.52 | 50.29 ± 6.10 | 0.000*** | |
70.94 ± 6.29 | 72.58 ± 4.58 | 0.493 | |
63.94 ± 5.80 | 64.29 ± 4.19 | 0.876 | |
108.46 ± 7.80 | 113.86 ± 6.81 | 0.072 | |
2.25 ± 7.20 | 5.28 ± 4.78 | 0.272 | |
46.46 ± 4.28 | 48.28 ± 3.54 | 0.224 | |
74.75 ± 7.30 | 75.86 ± 4.59 | 0.689 | |
-0.73 ± 3.43 | -1.50 ± 2.04 | 0.558 | |
33.23 ± 5.75 | 37.29 ± 6.29 | 0.068 | |
64.17 ± 3.77 | 64.29 ± 4.15 | 0.934 | |
33.18 ± 3.98 | 32.14 ± 5.98 | 0.504 | |
41.22 ± 4.11 | 41.28 ± 4.23 | 0.972 | |
60.88 ± 7.16 | 64.57 ± 7.13 | 0.180 | |
168.34 ± 7.67 | 174.00 ± 7.58 | 0.076 | |
44.01 ± 4.52 | 50.50 ± 6.65 | 0.001** | |
70.95 ± 6.28 | 72.30 ± 4.95 | 0.603 | |
63.94 ± 5.79 | 64.17 ± 4.57 | 0.926 | |
108.47 ± 7.78 | 114.33 ± 7.33 | 0.069 | |
2.28 ± 7.21 | 4.58 ± 4.82 | 0.439 | |
46.47 ± 3.90 | 48.00 ± 3.79 | 0.346 | |
74.73 ± 7.28 | 76.50 ± 4.68 | 0.556 | |
-0.73 ± 3.42 | -1.61 ± 2.21 | 0.532 | |
33.25 ± 5.75 | 37.00 ± 6.84 | 0.118 | |
64.16 ± 3.76 | 64.50 ± 4.50 | 0.828 | |
33.14 ± 4.04 | 33.83 ± 4.35 | 0.677 | |
41.20 ± 4.12 | 42.16 ± 3.86 | 0.574 | |
60.86 ± 7.15 | 65.67 ± 7.14 | 0.106 |
Notes: n: Sample size; **
Association between rs1793953 polymorphism and cephalometric values in the total sample.
rs1793953 | ||||
---|---|---|---|---|
CC ( | TT ( | CT ( | ||
168.16 ± 8.63 | 168.05 ± 6.89 | 168.90 ± 7.98 | 0.706 | |
43.78 ± 5.23 | 44.64 ± 4.68 | 43.93 ± 4.46 | 0.462 | |
71.21 ± 5.73 | 71.43 ± 4.84 | 70.57 ± 7.28 | 0.588 | |
63.59 ± 5.67 | 63.84 ± 4.81 | 64.16 ± 6.43 | 0.838 | |
108.49 ± 8.07 | 109.10 ± 7.54 | 108.29 ± 7.97 | 0.751 | |
1.04 ± 6.00 | 1.63 ± 6.95 | 3.31 ± 7.59 | 0.106 | |
46.36 ± 4.22 | 46.70 ± 3.30 | 46.41 ± 4.22 | 0.836 | |
75.02 ± 5.65 | 74.39 ± 8.49 | 74.98 ± 6.69 | 0.816 | |
-0.95 ± 3.40 | -0.75 ± 3.21 | -0.68 ± 3.55 | 0.908 | |
33.07 ± 6.01 | 33.46 ± 5.99 | 33.34 ± 5.62 | 0.940 | |
64.17 ± 3.99 | 64.18 ± 3.55 | 64.16 ± 3.88 | 0.998 | |
33.10 ± 4.30 | 33.00 ± 4.03 | 33.29 ± 3.98 | 0.873 | |
40.56 ± 4.28 | 41.44 ± 3.83 | 41.29 ± 4.25 | 0.506 | |
61.34 ± 5.43 | 62.21 ± 5.59 | 59.93 ± 8.52 | 0.066 |
Note: n: Sample size.
Of the aetiological factors in determining a Class III skeletal pattern, genetics plays a major role and genetic inheritance may guide the determination of the treatment of choice.16,17 The
The candidate genes selected for the present study were separately investigated in MR and MP cases as common features associated with a Class III skeletal pattern.2,4,19,20 In addition, there has been no prior genetic study investigating the
In the MP group, a positive correlation was found between statural height and all measurements, but particularly with ramus height. Height was correlated with mandibular length measurements rather than maxillary length measurements. Unlike the long bones, the mandible has no epiphysial cartilage; however, the growth pattern and morphological characteristics are comparable. In addition, the growth process is not dependent on sutures, unlike in the maxilla. Thus, statural height seemed to be mainly correlated with mandibular measurements.21
No significant difference was found in the cephalometric comparisons between the genotypes of the
Tomoyasu et al.13 noted a correlation between ramus height and the
Bayram et al.15 investigated the P561T and C422F variants of the
When the cephalometric characteristics of genotypes were compared, the result was significant for the
Within the total sample, ramus height was significantly increased in individuals who possessed the
The major limitation of the present study was the sample size because of the low frequency of the chosen genetic markers. In the current research of a population of Turkish individuals, an association study was conducted while investigating the genetic background of a skeletal Class III malocclusion to evaluate the status of genes previously identified as candidates in other ethnic groups. However, some researchers have indicated the importance of epigenetic and other mechanisms that change gene expression.25 These are considered important factors in dento-facial growth and facial phenotype and should be identified in the parameters that influence malocclusions.25 Linkage analyses conducted in future investigations will help clarify how genetic factors influence craniofacial structure at the molecular level. By examining different candidate genes and different domains of the genes evaluated in the present study, a possible genetic aetiology will likely become clearer.
Within the limitations of the present study, the
The authors declare that there is no conflict of interest.
This work was supported by Aydın Adnan Menderes Research Projects [DHF-15011].
All procedures performed in studies of human participants were in accordance with the ethical standards of the institutional and/or national research committee (the Ethics Committee of Ege University, Medicine School [16-6/17]) and with the 1924 Helsinki Declaration and its later amendments or comparable ethical standards. All patients and legal guardians gave written informed consent before participation.
The data underlying this article will be shared on reasonable request by the corresponding author.
The full protocol of this study can be accessed from the National Thesis Database of Turkey (tez.yok.gov.tr).