Type of article: Research article “Association of ABO blood groups with craniofacial morphology among orthodontic patients of Kathmandu district”

Background: The craniofacial morphology and blood groups both are related to genetic components, hence it can be hypothesized that blood groups have an association with craniofacial morphology. Some studies showed the relationship whereas others could not �nd any relationship that may be due to geographic diversity of the population. The aim of this study was to �nd out the relationship between ABO blood groups and craniofacial morphology among orthodontic patients of Kathmandu district. Materials and Methods: In this cross sectional study, a total of 385 participants (age range from 13-45 years) were selected among the orthodontic patients who came for orthodontic treatment in private orthodontic clinics. After obtaining written consent, all the patient’s demographic information were recorded and lateral cephalograms were obtained from the patient’s record. Blood group of all the participants was recorded. Results: The study found that among the total of 385 participants, 162 (42.07%) were male while 223 (57.93%) were female and the mean age was 16.31±4.38 years. Twenty cephalometric parameters depicting craniofacial morphology were digitally analyzed using lateral cephalogram. The prevalence of blood group O patients was highest (32.20%) followed by blood group B (30.64%), blood group A (29.88%) and blood group AB (7.28%). Statistical analysis with one way ANOVA was used for association of numerical data and blood groups that revealed nine out of twenty cephalometric parameters were statistically signi�cant among different blood groups (p<0.05). Tukey post hoc test was done to �nd out where the signi�cant difference occurs among the groups. Conclusions: The evaluation of the relationship between blood group and craniofacial morphology revealed that blood groups have association with some craniofacial parameters. This suggest, there may be some genetic in�uence of ABO blood group on craniofacial morphology


Background
Blood groups are inherited through genes on chromosome number 9 and ABO blood types do not change as a result of environmental in uences during life.Malocclusion has been shown to affect oral health, increased prevalence of dental caries and can cause temporomandibular joint disorders.The etiology of malocclusions is multi-factorial and is not attributed to a single speci c cause.Among various etiologies, genetics plays a signi cant role in causing malocclusions.The relative role of genetic and environmental factors in the etiology has been a matter of discussion and controversy in orthodontics [1].
Studies can reveal relationships between malocclusions and some genetic characteristics or accompanied diseases, that help to recognize and treat them.Relationship between the ABO blood group system and some oral diseases such as malocclusions is one of the important genetic characteristics.
With the discovery of ABO blood groups and some enzyme polymorphs, it could be possible to determine the zygosity of twins, which are especially helpful in twin studies concerning the role of heritability of malocclusion [1,2].
Landsteiner rst described the existence of serologic differences between individuals and classify people into four groups depending on whether their red cells contained agglutinogen or not.The presence or absence of these antigens results in the four blood groups: A, B, AB, and O [3,4].
Although genetic factors appear to govern the basic skeletal form and size, environmental factors have much in uence on the bony elements [17,18].Cephlaometric radiograph is used both as a research and a clinical tool for the study of malocclusion and skeletal structure [19].A cephlaometric radiograph and cephalometric norms plays a signi cant role in assessing the anterioposterior jaw relation [20], class of occlusion [21], to formulate a treatment plan, and is a substantive tool in Orthodontics to aid orthodontic clinicians and research workers [22].
Limited studies have been conducted to nd the relationship between oral and dental diseases and ABO blood group that showed contradictory ndings that may be due to geographic diversity.This study was conducted to nd out relationship of blood groups with craniofacial morphology of Nepalese orthodontic patients which was lacking and hoped that these ndings will be helpful for further research.
The aim of this study was to determine the association between ABO blood groups and craniofacial morphology among orthodontic patients of Kathmandu district.

Methods
Three hundred eighty ve participants (age range from 13-45 years) were selected among the orthodontic patients who came for orthodontic treatment treated by same orthodontist (author) in private orthodontics clinics of Kathmandu District.Sample size for this study was determined by using n = Z 2 pq/d 2 , where Z = 1.96, value of p is taken as 0. 5, q = 1-p = 0.5, allowable error (d) = 0.05 and n is required sample size.Based on these parameters, the required sample size was 384.16 hence, total 385 patients were selected.
Inclusion criteria of this study werepatients who came for orthodontic treatment in Orthodontics clinic, Kathmandu, Nepal with identi ed blood group and who gave consent to this study.Patients were excluded who had previous orthodontic treatment and had systemic disease or Craniofacial anomalies/Congenital syndrome.Also participants who were unaware of their blood group and those who were not willing to share the information were excluded from the study.
Informed written consent was taken from patients or their parents.Blood group of the patient was noted in the data sheet from registered laboratory report or driving license provided by Government of Nepal.

Fig. 1 Digital measurements of craniofacial morphology on lateral cephalogram
Data obtained were transferred to MS-excel sheet.The data were double entered and analyzed in SPSS software version 21.0.(Armonk, NY: IBM Corp.) with con dence level set at 95% (P < 0.05) to test for signi cance.All procedures such as landmark identi cation, and measurements were repeated 4 weeks after the rst examination by the same investigator.Eighty patients were selected randomly to nd the errors associated with measurement and digitizing for intraobserver reliablility.To assess the reliability of the measurement, the intraclass correlation coe cients were performed and value lies between 0.87 and 0.95.
To determine method-error of cephalometric measurements, Dahlberg's formula was used and value was less than 0.68 degrees for angular and 0.39 mm for linear variables that considered to be within acceptable limit [23].

Results
This cross sectional study found that among the total of 385 participants, 162 (42.07%) were male while 223 (57.93%) were female (Fig. 2) and the mean age was 16.31±4.38years.

Fig. 2 Frequency of gender distribution
Out of 385 respondents, most of them were of the age group 13-18 years i.e. 45.72%, from the age group 19-25 years there were 33.25% respondents and from the age group of more than 25 years there were only 21.03%.
In the present study, the prevalence of blood group O patients was highest (32.20%) followed by blood group B (30.64%) then blood group A (29.88%) while the prevalence of blood group AB patients was least (7.28%).( Fig. 2)

Craniofacial morphology
Craniofacial morphology (SNA, SNB, ANB, Wits, Cond-A, Cond-Gn, Max-Mand, NSAr, SArGo, ArGoMe, SN-GoGn, FMA, ANS-Me, Max1-NA, Max1-SN, Mand1-NB, IMPA, Mx1-Mn1, UL-E and LL-E) were digitally analyzed using lateral cephalogram.Table 1 and 2 showed the results obtained by digital analysis of lateral cephalogram using Vistadent OC 1.1 software program.Statistical analysis with one way ANOVA was used for association of numerical data and blood groups that revealed nine out of twenty cephalometric parameters like Cond-A, Cond-Gn, Max-Mand, NSAr, SArGo, ArGoMe, Max1-SN, Mand1-NB and IMPA were statistically signi cant among different blood groups (p<0.05).Tukey post hoc test was done to nd out where the signi cant difference occured among the groups (Table 3).Table 1.The association of skeletal parameters between blood group A, B, AB and O.

Discussion
This cross sectional study provides information about craniofacial morphology among various blood groups.As the craniofacial morphology and blood groups both are related to genetic components, it can be hypothesized that blood groups have an association with craniofacial morphology.The purpose of this study was to identify such a possibility and to correlate ABO blood group and craniofacial morphology in orthodontic patients of Kathmandu district, Nepal.
Many studies revealed positive correlation of non O blood group with developing risk of ischemic heart disease, severe manifestations of atherosclerosis, and increased risk of infection with cholera [11,12,[24][25][26].While O blood group individuals have a 4% reduced risk of basal cell carcinoma,14% reduced risk of squamous cell carcinoma and reduced risk of pancreatic cancer [27].Along with this, increased risk of ovarian cancer in blood group B while Gastric cancer is more common in blood group A and least in group O.
Despite of several researches done so far in the medical eld, only limited researches that relates ABO blood groups with incidence of the oral diseases.The ndings of previous studies were contradictory as some showed relationship while others did not.The reasons for this variation may be due to geographical diversity [28][29][30][31].
Findings of Demir et al. showed the signi cant association of different ABO blood groups in the rates of colonization of periodontal pathogens in periodontal diseases [32].Other report showed that oral pathologies like dermatophytosis are common in blood group A [33].Study by Vivek et al. [34] showed blood group O had a greater chances for periodontitis while Gheisari et al. [35] showed blood group B have a greater likelihood of association with maxillofacial deformities and least with blood group A.
Blood groups and Rh antigen, both are hereditary.Gene for ABO antigens is present on the 9th chromosome and Rh antigen gene is on the 1st chromosome [36].
Based on antigen production, the alleles were termed A (produce A antigen), B (produce B antigen), and O (no antigen production) [37].Antigens also act as receptors for infectious agents so it has been associated with several diseases and deformities [38].Blood group O persons who lacks A and B genecoded glycosyltransferase express a fucosylated variant of the precursor [39].
Studies reported that blood group 'A' common among Eskimos, 'B' in Chinese and Indians, the group O in Americans, Canadian Indians, Czechoslovakians and Kenyans.
The distribution of ABO blood group varies regionally, ethnically and from one population to another.In the present study, the ABO blood group typing showed the same trend of prevalence as in the general Nepali population (O > B > A > AB) [40,41].This study shows the highest frequency of blood group O (32.20%), followed by B (30.64%),A (29.88%) and least with AB (7.28%).
Statistical analysis with one way ANOVA revealed nine out of twenty cephalometric parameters like Cond-A, Cond-Gn, Max-Mand, NSAr, SArGo, ArGoMe, Max1-SN, Mand1-NB and IMPA were statistically signi cant among different blood groups (p<0.05).This indicates some genetic in uence on craniofacial morphology.
The results of this study is contradictory with the study of Shokor et al.,[48] that there was no genetic in uence of ABO blood group in relation to variation in craniofacial morphology so the prediction of malocclusion cannot be made in the respective blood group.
Genetic factors responsible for the basic skeletal form and size while environmental factors have much role on the bony elements [49,50].Other study stated that environmental factors also played an important role in genetically-in uenced facial types and growth patterns [51].It has been found by several investigators that different ethnic groups have different dentofacial patterns [52,53].
Long-term multicenter collaborative studies with diverse population groups with greater sample size and inclusion of healthy control are suggested to make more comprehensive assessment for de nitive establishment of their association between blood group and craniofacial morphology.

Conclusions
In this study, the results obtained showed a higher fraction of blood group O (32.20%) followed by B (30.64%) then A (29.88%) and least with blood group AB (7.28%) among orthodontic patients.Statistical analysis with one way ANOVA revealed that blood groups have association with some craniofacial parameters.This suggests that there is some genetic in uence of ABO blood group on craniofacial morphology.The derived results can be used as a stepping stone in order to focus the research on correlation between the blood group antigens and development of malocclusion targeting highly susceptible individuals and developing customized treatment strategies.

Figures
Figures

Figure 1 Digital
Figure 1

Table 2 .
The association of dental and soft tissue parameters between blood group A, B, AB and O.

Table 3 .
Tukey post hoc test for intergroup comparison of dento-skeletal parameter between different blood groups

Table
The association of dental and tissue parameters between blood group A, B, AB and O. Table Tukey hoc test for intergroup comparison of dento-skeletal parameter between different blood groups 95% CI: 95% con dence interval; ANOVA: Analysis of Variance Declarations