Balkan Journal of Medical Genetics

ETHNIC VARIATION IN INTERLEUKIN-6 –174 (G/C) POLYMORPHISM IN THE MALAYSIAN POPULATION
Gan G-G*, Subramaniam R, Lian L-H, Nadarajan VS
*Corresponding Author: Professor Dr. Gin-Gin Gan, Department of Medicine, Faculty of Medicine, University Malaya, Lembah Pantai, Kuala Lumpur, Malaysia; Tel.: +603-79-492-429; Fax: +603-79-556-936; E-mail: gangg@ummc.edu.my
page: 53

DISCUSSION

Cytokine gene polymorphism has been demonstrated in many articles resulting in interindividual variation of transcriptional regulation and subsequently different serum level of cytokines. It has been well established that frequency of the different cytokine gene allele varies among the different populations. The frequency of the IL-6 gene polymorphism had also been extensively studied in different populations. Ethnic differences were well demonstrated among all major populations. It has been reported that –174C allele was completely absent in Japanese and significantly lower in Koreans and Chinese compared with Caucasians [7,16,19,20]. Similar findings have also been demonstrated in Africans and the remaining Eastern Asian populations [9,10,11-13,15,16,21-23] (Table 3). It is also interesting to note the absence of the homozygous C genotype among the Chinese, Korean and African populations [9,16,19,22,23]. In this study, the allele frequency of –174C was only 9.0%, much lower than those reported in the European population [10,13]; 85.0% of the subjects carried the GG genotypes and only 2.0% carried the CC genotype. However, there were significant differences in the distribution of IL-6 –174 (G/C) between the three ethnic groups. There was a complete absence of the –174C polymorphism in the Chinese subjects, which is similar to that reported in the Singapore Chinese populations [9]. This is of no surprise as Malaysian Chinese and Singapore Chinese are very closely related due to geographical and historical reasons. In contrast, the C allele frequency was significantly higher (19.0%) in the Indians in this study compared with the other two ethnic groups. The IL-6 –174 (G/C) polymorphism was relatively more evenly distributed in Indians: 66.0% carried the GG genotype, 30.0% carried the GC genotype and 4.0% carried the CC genotype. Study of Indian populations in India had demonstrated the difference in the IL-6 –174 (G/C) polymorphism among the North and South Indians [11,24]. There was a higher frequency of the C allele in North Indians compared to South Indians, 32.4 vs. 15.5%, respectively. The majority of the South Indians studied (72.0%) carried the GG genotype and only 2.9% carried the CC genotype [24]. Our study reported similar findings with the South Indian rather than the North Indian populations. The most likely reason could be due to the fact that most of the Indians in Malaysia were of South Indian ancestry. The –174C allele was only detected in 4.0% of Malays. There had not been any reports on the frequency of IL-6 –174 (G/C) polymorphism in the MaInterleukin-6 has been extensively studied and has been implicated in many diseases, including coronary artery disease, cancers and Alzheimer’s disease. In a meta-analysis reported by Liu et al. [25], the IL-6 –174 (G/C) polymorphism was associated with cancer risk in African populations but not in Caucasian population. Similar meta-analysis by Xu et al. [26] had also demonstrated that there was a possible association of the IL-6 –174 (G/C) polymorphism with cancer risk among Asians and Africans. A recent meta-analysis of 20 studies suggests that the IL-6 –174 (G/C) polymorphism was associated with increased risk of coronary heart disease among Asians [27]. In the subgroup analysis, it was suggested that individuals with the C allele might have a higher risk of coronary heart disease. Interestingly, studies involving Asian populations had demonstrated that Asian Indians were at greater risk of coronary heart disease compared to other ethnic populations [28,29]. After adjusting for the other risk factors of coronary artery disease, the Indian population remained one of the risk factors [30]. Hence, it is of interest that a higher frequency of the C allele was found in Indians in this study cohort. Therefore, this study serves as an important reference study for the Malaysian population and also to provide data for the least studied populations, e.g., Malays and Indians. The result of this study can be used as a reference point for future studies in determining risk factors and association of the mentioned diseases in the Malaysian population. Declaration of Interest: This study was funded by the University Malaya Research Grant RG307/11HTM. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

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