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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 7  |  Issue : 3  |  Page : 170-173

Distribution of Dopamine Receptor 2 (DRD2) rs1800497 Polymorphisms In Cyclist


1 Marmara University Faculty of Dentistry Basic Medical Sciences, Medical Biology and Genetics, Istanbul, Turkey
2 Nisantası University, School of Physical Education and Sports, Istanbul, Turkey
3 Uskudar University, Laboratory of Medical Genetics and Molecular Diagnostics, Istanbul, Turkey

Date of Submission12-Nov-2020
Date of Decision04-Dec-2020
Date of Acceptance16-Nov-2020
Date of Web Publication25-Dec-2020

Correspondence Address:
Korkut Ulucan
Haluk Türksoy Sokak No: 14, Altunizade 34662, İstanbul
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jnbs.jnbs_34_20

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  Abstract 


Genetic and environmental factors are important determinants of the athletic performance. Sports genetic determines certain alleles for the identification of the genes that affect athletic performance. Comprehensive researches including the biology of mental properties are accumulating due to the improvement of the information of molecular biology. Dopamine is an important neurotransmitter of the dopaminergic system that affects the athlete mentally and psychologically. In this study, our goal is to determine the genotype and allele distributions of the DRD2 rs180047 polymorphism in the cyclists. Nineteen cyclists and 52 sedentary individuals (controls) participated in our study. Genotyping was carried out by real-time polymerase chain reaction after DNA was isolated from buccal epithelial cells. In our cohort, AG and GG genotypes were detected as 6 (32%) and 13 (68%), respectively. In the control group, the respective AA, AG, and GG genotypes were detected as 9 (17%), 18 (35%), and 25 (48%). No statistically significant difference was detected in terms of genotype distribution between the two groups (P=0.1107). When allelic distributions were examined, in the athlete cohort, A and G allele numbers were counted as 6 (16%) and 32 (84%), respectively. In the control group, the same alleles were counted as 36 (35%) and 68 (65%). There was no statistically significant difference in terms of alleles in our study cohort (P = 0.0295). In our cohort, GG genotype and the G allele of the DRD2 rs1800497 polymorphism were dominant. Recent studies showed the association of the A allele with addiction. Therefore, we hypothesized the association of the related allele and success in cyclists. Although we were unable to find a statistically significant difference, we suggest to analyze the same polymorphism in athletes with different sports branches to fulfill the role of the given polymorphism.

Keywords: Cyclist, DRD2, genetics, polymorphism, sports


How to cite this article:
Silar Ç, Karagöz E, Polat T, Yilmaz ÖÖ, Aslan BT, Doğan CS, Baltacioğlu BS, Kaman T, Ulucan K. Distribution of Dopamine Receptor 2 (DRD2) rs1800497 Polymorphisms In Cyclist. J Neurobehav Sci 2020;7:170-3

How to cite this URL:
Silar Ç, Karagöz E, Polat T, Yilmaz ÖÖ, Aslan BT, Doğan CS, Baltacioğlu BS, Kaman T, Ulucan K. Distribution of Dopamine Receptor 2 (DRD2) rs1800497 Polymorphisms In Cyclist. J Neurobehav Sci [serial online] 2020 [cited 2021 Apr 12];7:170-3. Available from: http://www.jnbsjournal.com/text.asp?2020/7/3/170/304926




  Introduction Top


The need for research in athletic performance is increasing due to the development of technology and science in sports. There are many factors determining success in sports. Training types and diversity, genetic factors, epigenetics, diet patterns, motivation, equipment, and other environmental factors are some of them. [10,11] Mental and physical factors make up the overall athletic performance and increase with the progress in environmental factors such as training and nutrition. Having information about the genetic structure in athletes is important to have certain functions and personal training programs in both individual and team sports.[13]

Cycling activities require long-term endurance and strength. Muscle volume and muscle fiber types affect many biomechanical variables like pedal force in cyclists. Therefore, it effects the cycling performance. There are also many different types of cycling and the performance in these types varies accordingly.

Dopamine is an important neurotransmitter that significantly effects the dopaminergic system and physical activities that we face in our daily routine. Apart from these activities, it affects exercise and athletic performance to a great extent. It provides regulation of neurological functions and communication between neurons that are crucial in motor activities. Factors affecting the central nervous system are directly related to psychology. Therefore, dopamine affects mentally athletic performance.[1]

There are five different types of dopamine receptors: DRD1, DRD2, DRD3, DRD4, and DRD5.[2] DRD2 gene that encoding dopamine metabolism is localized at 11q22-q23. Some polymorphisms have been identified in the gene, one of which is rs1800497 (G/A transition). The G allele in the DRD2 rs1800497 polymorphism is considered wild type and related with the high number of the receptor molecules on the cell membrane. The A allele is considered to be polymorphic allele and studies to date have linked the A allele with lower receptor numbers and lower dopamine levels.[3] Dopaminergic neurons and regions in the brain also appear to play a role in addiction and with some neuropsychiatric disorders.[4]

In the present study, we aimed to examine the distribution of receptor 2 (DRD2s) rs1800497 in cyclists and compare the results with the sedentary individuals. This report, according to the best of our knowledge, is the first which is carried out in cyclists.


  Materials and Methods Top


Ethics committee approval

The protocol used in the present study was approved by the Üsküdar University Ethics Committee and was performed in accordance with the principles of the Declaration of Helsinki II. All participants signed consent forms containing all the information such as the study protocol, results and evaluation of the results.

Study subjects

Nineteen cyclists were participated in our study. Fifty-two sedentary individuals also participated as a control group. All the volunteers had no transmitted genetic anomalies. The study protocol was approved by the Üsküdar University Ethical Committee and was in line with the principles of the Declaration of Helsinki II. Before the study, all participants signed consent forms containing all the information such as the study protocol, results, and evaluation of the results.

Genotyping

DNA isolations from buccal epithelial cells of the athletes were carried by the commercially obtained PureLink DNA isolation kit (Invitrogen, Van Allen Way, Carlsbad, CA, USA). Genotyping of the DRD2 rs1800497 polymorphism was performed using quantitative real-time polymerase chain reaction (PCR) (Applied Biosystems StepOnePlus, ABD.), using a TaqMan Genotyping assay (cat. no. 4362691; Thermo Fisher Scientific, Inc.). The manufacturer's protocols were followed for the genotyping processes. PCR conditions were 60°C for 30 s and 95°C for 10 min, followed by 40 cycles of 15 s at 95°C for and 1 min at 60°C. Finally, 60°C for 30 s was applied for post-PCR reading. The fluorescent signal was detected at the pre-PCR, amplification at the end of each cycle, and post-PCR reading steps. G and A alleles were determined using Taqman VIC and FAM primers, respectively [Figure 1]. The sequences of the Taqman Probe used for genotyping are listed in [Table 1].
Figure 1: Quantitative polymerase chain reaction amplification of the AG genotype and GG genotype of DRD2 rs1800497 polymorphism. FAM indicates the G allele (blue curve), whereas VIC (green curve) indicates the A allele. The blue and green curves indicate the heterozygous genotype of AG (a), whereas the single blue curve indicates the homozygous genotype of GG (b)

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Table 1: Genotypic and allelic distribution of the DRD2 rs1800497 polymorphism in the study cohort

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Statistical analysis

Genotype distribution and allele frequencies between athletes and controls were compared by Chi-square test, using the SPSS (version 18.0 for Windows, SPSS, Chicago, IL, USA) program. P < 0.05 value was accepted as statistically significant.


  Results Top


In our cohort, 13 (68%) of 19 players had GG and 6 (32%) of them had AG genotypes. No AA genotype was detected. When allele distributions were examined, it was observed that the percentage of A allele was 16% and the G allele was 84%. In the control group (n = 52), 9 individuals had AA, 18 individuals had AG, and 25 individuals had GG genotype. A allele was counted as 36 (35%) and G allele as 68 (35%). The genotype and allele number distributions of the athletes are summarized in [Table 1].


  Discussion and Conclusion Top


Variations in the DRD2 gene can affect athletic performance. Low dopamine level due to DRD2 polymorphisms may be a parameter that prevents success in sports. Low dopamine levels are associated with neurological diseases and hyperactivity as well as sports performance. Apart from that, high dopamine levels are also associated with abnormal brain function.[5] There are studies in which polymorphism is associated with sports addiction[16],[17][Table 2].
Table 2: Sequences of the TaqMan probe used for genotyping DRD2 rs1800497 polymorphism

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Dopamine shows its biological effects by binding to its receptors (DRD2s). DRD1, DRD2, DRD3, DRD4, and DRD5 are the known five different dopamine receptors. Studies show that DRD2 receptors in neuronal membranes are higher in numbers who have the GG genotypes than in the AA genotypes (Grandy 1989).

In our cohort, AG and GG genotypes were detected as 6 (32%) and 13 (68%), respectively. A and G allele numbers and percentages were, respectively, 6 (16%) and 32 (84%). There were no statistically significant difference between athletes and controls.

There are few studies investigating the relationship between the DRD2 rs1800497 polymorphism and sports performance. Yüksel et al.[7] investigated the rs1800497 polymorphism in volleyball players. In their study, all the genotypes of all players were found as GG. Before, A allele has been poorly associated with addiction in sports. Özcan et al.[8] analyzed DRD2 rs1800497 polymorphism in sprinter and endurance athletes and reported that GG genotype and G allele were superior in the study cohort. Abe et al.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18] examined the COMT, DRD2, and DRD3 polymorphisms which have effect on dopaminergic nerve functions and reported that AA genotype of DRD2 rs1800497 polymorphism was lower when compared to AG and GG genotypes. [Figure 2] and [Figure 3]
Figure 2: Percentage of the genotype distributions of DRD2 rs1800497 polymorphism

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Figure 3: Percentage of the allelic distributions of DRD2 rs1800497 polymorphism

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In our study with 19 cyclists, the GG genotype was found higher than the AG genotype. There were no athletes with the AA genotype. At the same time, when we compare the G allele with the A allele, G allele is higher than the A allele. The results of our study were in agreement with the previous studies. Our results are similar to the findings of previous studies. The DRD2 A allele has been found to be associated with addiction. Studies have shown that the same allele is associated with sports addiction and athletic performance. Our study will contribute to the literature and support other studies in this field. It can help to prevent early psychological disorders encountered in athletes.[15]

Patient informed consent

Informed consent was obtained.

Ethics committee approval

The protocol used in the present study was approved by the Üsküdar University Ethics Committee and was performed in accordance with the principles of the Declaration of Helsinki II. All participants signed consent forms containing all the information such as the study protocol, results, and evaluation of the results.

Financial support and sponsorship

No funding was received.

Conflicts of interest

There is no conflict of interest to declare.

Author contribution area and rate

Çisem Şılar: data collection, formation of the article 20%

Esra Karagöz: data collection, formation of the article 20%

Tolga Polat: data collection, statistics 10%

Özlem Özge Yılmaz: laboratory assistance 10%

Begüm Su Baltacıoğlu: laboratory assistance 10%

Beste Tacal Aslan: laboratory assistance 10%

Canan Sercan Doğan: data collection 5%

Tuğba Kaman: data collection 5%

Korkut Ulucan: formation of the article 10%.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]



 

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