Keywords
polymorphism -
GHR gene - class III malocclusion - mandible prognathism
Introduction
Craniofacial morphology is influenced not only by genetic components but also by environmental
complexes. The effects of these components are related to size and craniofacial characteristics.
Growth hormone (GH) also has a vital role in the growth of the craniofacial complex
and its development through direct or indirect size regulation. The angular relationship
between craniofacial structures and GH receptor (GHR) affects mandibular condyle growth.[1]
[2]
The anterior pituitary gland facilitates the regulation of the maxillofacial complex
growth development, which produces GH. Insulin-like growth factor-1 (IGF-1) in the
axis plays a role in normal metabolism and thus significantly regulates the effect
on the growth and development of postnatal hard tissue. GH originates in the anterior
pituitary and produces GH, acting directly on tissues through IGF-I production.[1]
[3]
Several previous studies have investigated the association between the variants of
the GHR gene and craniofacial morphology in the population in general, and the results show
that class malocclusion in the cases of class III is more common in Asian populations
than in other populations. In addition, several studies have also reported a low incidence
of class III malocclusion (∼1–5%) in Caucasian, American, European, and African populations.
These results indicate that genetic factors play a role in craniofacial morphology.[4] This review aims to evaluate and discuss variant polymorphisms in GHR in different
populations.
Methods
Search Strategy
Electronic databases were used for the initial selection: PubMed (2000–2020) and Google
Scholar (2000–2020). No filters or restrictions were used in the search. Descriptors
were selected from previously searched Medical Subject Headings (MeSH) terms and the
most cited ones from relevant previous publications. Search was performed using the
following terms in MeSH and their combinations: “polymorphism, genetic” (MeSH term)
or “polymorphism, mononucleotide” (MeSH term) and “Growth hormone receptor” (MeSH
term) or “growth hormone-binding protein” (MeSH term) and “malocclusion, angle class
III” (MeSH term) or “protrusion” (MeSH term) or “mandible” (MeSH term) or “Skeletal
Class III Malocclusion” and “Population.” In addition, a manual search of the bibliographies
of the final selected articles was performed to identify any relevant articles that
were not previously identified. The detailed search protocol is explained in the Preferred
Reporting Items Stated by the Systematic Review and Meta-analysis (PRISMA; [Fig. 1]).
Fig. 1 PRISMA diagram
Eligibility Criteria
This study was conducted concerning the PRISMA.[5] The eligibility criteria were imposed as original, cross-sectional, case-control
studies that assessed whether polymorphisms in the GHR were associated with patients'
skeletal malocclusion of Angle's class III and mandibular protrusion. Unpublished
manuscripts, theses, dissertations, book chapters, and case reports were excluded.
Study Selection
Two reviewers independently read all retrieved article titles and abstracts. The full
text was obtained if a reviewer deemed the publication to meet the inclusion criteria.
Abstracts that were potentially eligible and those that did not provide sufficient
information were included in the full-text analysis. After evaluating the full text,
disagreements about eligibility were resolved by consensus, and when disagreements
persisted, a third reviewer was invited to make the final decision.
Data Extraction
Two reviewers independently performed data extraction. General information was collected
from each article. In addition, specific characteristics were collected: author/year,
ethnicity/country, age range, sample size, case definition, cephalometric analysis
methods used to assess facial measurements, molecular biology techniques, and authors'
conclusions.
Quality Assessment
Articles were scored on a 10-point standard scale for published recommendations to
assess the quality of epidemiological and genetic association studies. Each quality
criterion was rated as present (yes, score 1) and absent or uncertain (no, 0).[6] Two authors independently graded all articles. In any disagreement, a consensus
is reached on the final score. The final quality rating is the sum of all components,
and each item is assigned a rating from 0 to 10. Papers are divided into three categories
based on the following scores: (1) high methodological quality: eight or more criteria
are suggested; (2) medium methodological quality: five to seven criteria are proposed;
and (3) low methodological quality: four or more. The recommended standard is less
standardized. Therefore, this study was also divided into strong, moderate, and low-quality
evidence.
Result
The extracted data from the studies included in this review are listed in [Table 1]. Six studies were conducted on Asian populations,[1]
[2]
[7]
[8]
[9]
[10] and one study each was born in Turkey,[11] Egypt,[12] and Columbia.[13] Other results are the qualitative scores of the articles, presented in [Table 2]; seven studies were classified as high methodological quality.[1]
[2]
[7]
[9]
[10]
[12]
[13] One study was classified as methodological quality due to incomplete data reported
in the results section.[11]
Table 1
Characteristics of the included studies
No.
|
Title
|
Author (year)
|
Objective
|
Specimen
|
Polymorphism GHR
|
Mandible prognathism
|
Year of research
|
Research methodology
|
Population
|
Samples
|
Result
|
1
|
Growth hormone receptor gene variant and three-dimensional mandibular morphology
|
Nakawaki et al (2017)[1]
|
Examine the relationship between three-dimensional (3D) mandibular morphology and
growth hormone receptor (GHR)
|
Saliva
|
GHR genes rs6184 and rs6180
|
Mandibular length and volume were measured by Autotracer in the outer circumference
of the cortical bone in all slide using Analyze
|
|
|
Japanese
|
178
|
Associated between GHR single nucleotide polymorphisms (SNPs) rs6180 with distances
left and right coronoid
|
2
|
Association of the P516T and C422F polymorphism of the growth hormone receptor gene
with facial dimensions
|
Dalaie et al (2019)[7]
|
Evaluate growth hormone receptor (GHR) gene polymorphism in relation to facial dimensions
|
Blood
|
Polymorphism of GHR genes P516T and C422F
|
Mandibular prognathism group: skeletal class III appearance (ANB and Wits less than
zero) and mandibular prognathism (SNB > 82 degrees);
Control group: patients' appearance 2 degrees ≤ ANB ≤ 4 degrees and 0 mm < Wits ≤ 2 mm
|
2015–2016
|
Observational case-control study
|
Iranian
|
125: 65 mandibular prognathic; 60 control
|
•No correlation between mandibular prognathism and SNPs rs6184
•P516T polymorphism associated with ramus and lower facial height in mandibular prognathism
|
3
|
The P516T polymorphism of the growth hormone receptor gene has an inhibitory effect
on mandibular growth in young children
|
Sasaki et al (2009)[8]
|
Assess whether this mutation affects mandibular during early childhood
|
Saliva
|
Single nucleotide polymorphism GHR gene P516T
|
Cephalometry trace for mandibular size (Cd-Go, ramus length; Pog'-Go, mandibular body
length and Gn-Cd mandibular length)
|
|
|
Japanese
|
60: 33 mandibular prognathic; 27 control
|
P516T heterozygous mutation did not account for the difference between mandibular
protrusion and normal occlusion
|
4
|
Association analysis between rs6184 and rs6180 polymorphism of growth hormone receptor
gene regarding skeletal-facial profile in a Columbian population
|
Tobón-Arroyave et al (2018)[13]
|
Examine the association between the rs6184 and rs6180 polymorphic variants of the
growth hormone receptor (GHR) gene and skeletal-facial profile in Columbian people
|
Saliva
|
Single nucleotide polymorphisms (SNPs) GHR rs6180, rs6182, and rs6184
|
Analyze skeletal-facial profile, lateral cephalogram, with digital pan/ceph system
|
|
Cross-sectional, observational, analytic study
|
Columbian
|
306
|
Result do not support that rs6180 SNP in the gene GHR rs6184 alone or in combination
with other SNP in GHR may account for significant horizontal and longitudinal variations
in mandibular morphology
|
5
|
Association of growth hormone receptor gene variants with mandibular form in an Egyptian
population
|
Adel et al (2017)[12]
|
Confirm GHR variants rs6180 and rs6184 associated with variations in mandibular form
|
Saliva
|
Single nucleotide polymorphisms rs6180 and rs6184
|
11 points from lateral cephalogram and 6 from posterior anterior cephalogram: Point
A (the most posterior on the anterior contour of the upper alveolar process); Point
B (the most anterior on the anterior contour of the lower alveolar process); Cd (condylion);
Cor (coronoid); Gn (gnation); Go (gonion); Id (infradentale); Me (menton); N (nasion);
Pog (Pogonion); S (sella turcica)
|
|
Cohort
|
Egyptian
|
191
|
No correlation between the rs6180 variant and mandibular form; rs6184 frequency very
low; the present study shows that both the rs6180 and rs6184 variants have no association
with variations in the mandibular form in the Egyptian population
|
6
|
Relationship between P516T and C422F polymorphism in growth hormone receptor gene
and mandibular prognathism
|
Bayram et al (2014)[11]
|
Evaluate allele and genotype frequencies of the P516T and C422F polymorphic sites
of the GHR gene and the relationship between mandibular prognathism and these two SNPs
|
Blood
|
Single nucleotide polymorphisms P516T and C422F
|
Mandibular prognathism group: ANB and Wits values less than 0 degrees; Control Group:
ANB angle 2–4 degrees and Wits value 0–2
|
|
|
Turks
|
200: 101 class III malocclusion after or before orthognathic surgery; 99 normal occlusion
|
C422F and P516T heterozygous polymorphisms of the GHR gene did not justify the difference
between the mandibular prognathic group and control group in this population; subjects
with CA genotype of P516T have a greater effective mandibular length (Co-Gn) and lower
face height (ANS-Me) than those with genotype CC
|
7
|
Association of the growth hormone receptor gene polymorphism with mandibular height
in a Korean population
|
Kang et al (2009)[9]
|
Study the association between a GHR polymorphism (d3/fl-GHR) that result in genomic
deletion of exon 3 and craniofacial morphology and to study association between GHR
genotypes in exon 10 and craniofacial morphology
|
Saliva
|
Single nucleotide polymorphisms (SNPs) C422F (rs6182), S473S (rs6176), P477F (rs6183),
I526L (rs6180), and P516T (rs6184)
|
Cranial base length (nasion sella; N-S), maxillary length (A'-PTM'), overall mandibular
length (gnation-condylion; Gn-Co), mandibular corpus length (pogonion-gonion; Pog-Go),
and mandibular ramus height (condylion-gonion; Co-Go)
|
|
|
Korean
|
159: 87 class I, 44 class II, and 28 class III
|
There is a significant association between the P561T and C422F polymorphisms of GHR
and mandibular ramus height in a Korean population
|
8
|
Further evidence for an association between mandibular height and growth hormone receptors
(GHR) gene in Japanese population
|
Tomoyasu et al (2009)[2]
|
Confirm the SNPs in the GHR gene are associated with mandibular height
|
Saliva
|
Single nucleotide polymorphisms C422F (rs6180), S473S (rs61176), P477F (rs6183), I526L
(rs6180), and P561T (rs6184)
|
Measured cranial base length (nasion-sella), maxillary length, overall mandibular
length (gnation–condylon), mandibular corpus length (pogonion-gonion), and mandibular
ramus height (condylion-gonion)
|
|
|
Japanese
|
167
|
There is an association between GHR polymorphisms P516T and C422F, and mandibular
ramus height
|
9
|
Growth hormone receptor gene variant and mandibular height in the normal Japanese
population
|
Yamaguchi et al (2001)[10]
|
Evaluate quantitatively the relationship between craniofacial morphology and the Pro516Thr
(P516T) variant in the GHR gene
|
Blood
|
Single nucleotide polymorphism GHR P561T
|
Cephalometric reference points and lines used to assess: N-S cranial base length;
A'-PTM maxillary length; Co-Go mandibular ramus length; Go-POG mandibular corpus length;
Co-Gn overall mandibular length; ANB position of maxilla and mandible
|
|
|
Japanese
|
100: 50 men; 50 women
|
The normal Japanese population without P516T had significantly greater mandibular
ramus length; there is relationship between the P516T variant at the GHR gene locus
and mandibular length
|
Table 2
Methodological scoring protocols
Criteria evaluated
|
Dalaie et al (2019)[7]
|
Tobón-Arroyave et al (2018)[13]
|
Adel et al (2017)[12]
|
Nakawaki et al (2017)[1]
|
Sasaki et al (2009)[8]
|
Bayram et al (2014)[11]
|
Kang et al (2009)[9]
|
Tomoyasu et al (2009)[2]
|
Yamaguchi et al (2001)[10]
|
Control group
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
Hardy–Weinberg equilibrium
|
1
|
1
|
0
|
1
|
0
|
1
|
1
|
1
|
0
|
Case group
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
Reproducibility
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
1
|
Blinding
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
Power calculation
|
0
|
0
|
0
|
0
|
1
|
0
|
0
|
0
|
0
|
Statistics
|
1
|
1
|
1
|
1
|
1
|
0
|
1
|
1
|
1
|
Corrected statistics
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
Independent replication
|
1
|
1
|
1
|
1
|
0
|
0
|
1
|
1
|
1
|
Compilation of reported association and outcomes
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
Score
|
8
|
8
|
7
|
8
|
4
|
6
|
8
|
8
|
7
|
Discussion
This review suggests that GHR polymorphisms are related to craniofacial development,
particularly the mandible, and may be genetic markers of mandibular protrusion.[14] GH is a crucial somatic cell growth regulator through its pleiotropic effect on
metabolism systemically and local bone growth plates; it is secreted by the pituitary
gland that binds to receptors on the cell surface of target tissues (GHRs) which will
trigger a cascade of rapid intracellular signaling.[15]
The biological role of growth hormone is to bind to the GHR, so the protein on almost
every cell membrane in the body has domains of a 246 long extracellular (GH-binding)
amino acid, the transmembrane, and a 350 long intracellular (cytoplasmic) amino acid.
The GHR protein itself consists of a total of 638 residues. Furthermore, GH binds
to GHR and induces a serial conformational event in homodimer receptors, promoting
receptor interaction through their relative rotation and location closer to the cell
membrane.[16]
The location of the GHR gene is proximally on the short arm of chromosome 5 (region p13.1-p12) that encodes
the human GHR protein. Nine coding exons are contained in these genes spanning at
least 87 kilobase pairs of chromosome 5. The last 11 base pairs of the untranslated
5′ region are encoded by exon 2 and the first amino acid of the extracellular domain.
The remaining bulk extracellular domains are encoded by exons 3 to 7; exon 8 encodes
the transmembrane domain; and exons 9 to 10 encode the untranslated intracellular
and 3′ domains. Moreover, the gene contains several additional exons in the 5′ region,
which are not translated.[16]
The family of transmembrane cytokine receptors from which GHR is derived has no intrinsic
enzymatic activity; the cytoplasmic domain of GHR associates with tyrosine kinase
Janus kinase 2 (JAK2) rather than activating intracellular signaling.[15] An enzyme-like receptor is a protein that passes through the membrane only once.
Enzyme-linked receptors have hormone-binding sites outside the cell membrane, while
on the inside are the catalytic or enzyme-binding sites. Hormones bind to the extracellular
portion of the receptor; thus, enzymes directly inside the cell are activated. A small
number of various hormones are facilitated by receptor tyrosine kinase signaling (e.g.,
fibroblast growth factor, growth factor, hepatocyte growth factor, IGF-2, leptin,
prolactin, vascular endothelial growth factor).[17] Binding of growth hormone to GHR results in rapid binding of JAK2; JAK activation
is associated with most pathways in GHR and plays a crucial role in signal transduction
in the pro-growth axis. GHR is primarily transduced through the JAK2 signal transducer
and activator of the transcription (STAT) pathway.[18]
The GH promotes dimerization upon binding the two GHR proteins, resulting in a conformational
change triggering the activation of the associated JAK2 tyrosine kinase due to the
exposure to its kinase domain. Furthermore, the activation of JAK2 will induce cross-phosphorylation
of two adjacent JAK2 proteins and phosphorylation of tyrosine residues in the cytoplasmic
domain of GHR. Signal converters and activators of transcription (STAT) are recruited
to phosphorylated tyrosine, where they become substrates for JAK2. While STAT1, STAT3,
and STAT5a can also be recruited to the GHR, STAT5b is an essential mediator of GH
signaling.[13] Members of the JAK family are mainly expressed in different cell types, except for
JAK3, whose expression is restricted to the hematopoietic lineage. JAK1 and JAK2 are
involved in various physiological activities such as hematopoiesis, immunity, development,
and growth.[19]
A polymorphism in the GHR results in a deletion of exon 3 (d3-GHR) with a homozygous
allele frequency of approximately 12%. The entire GHR exon 3 sequences were deleted,
resulting in a GHR protein lacking 22 amino acids in the extracellular binding domain.
The resulting protein (d3-GHR) contains aspartate residues instead of alanine residues
at the exon 2 to 4 junction. The consequent deletion affects exons and sections on
introns 2 and 3.[12]
[16]
The mandibular protrusion is a strange relationship between the mandible and the base
of the skull, characterized by excessive protrusion of the mandible. Facial contours
and soft tissue relationships can quickly diagnose defects. The lower area is enlarged
due to the protrusion of the mandible. Some patients may develop severe long-face
syndrome. The prominence of the jaw is also associated with incorrect or no lip contact.
Lip and mouth closure is not feasible in many patients because this feature is often
associated with anterior crossbite or open bite at the anterior or lateral occlusal
site. For most patients, the side effects are not only facial aesthetics but also
the ability to speak, chew, and pronounce.[20]
Angle class III malocclusion prevalence varies widely between and within populations,
with the highest incidence in Asian populations.[1]
[2]
[7]
[8]
[9]
[10] The etiology of class III malocclusion is very broad and complex, related to environmental
and genetic factors. Class III malocclusion may originate from teeth or bones, so
accurate classification of malocclusion is essential for good clinical management.
This article describes the optimal timing and management of class III malocclusion
in adolescence. Class III malocclusion was relatively high in the Chinese and Malaysian
populations (15.69 and 16.59%, respectively), while the prevalence in the Indian population
was relatively low compared with other ethnic groups. In the United States, the prevalence
of class III malocclusion is only approximately 1% of the general population and only
5% of orthodontic patients.[1]
[2]
[7]
[8]
[9]
[10]
[21]
Conclusion
Our systematic review further demonstrated the association between rs6180, rs6182,
and rs6184 polymorphic variants in GHR and condylion-gonion measures in Asian populations.
On the other hand, the evidence for the relationship between Colombian and Egyptian
people was low.