ABSTRACT
BACKGROUND: Polymorphism in promoter region can change the expression of genes, which may be associated with susceptivity of diseases. Gene polymorphism of interleukin-6 (IL-6) promoter is associated with nationality and many diseases. Different nationalities often display different characteristics of gene polymorphism.OBJECTIVE: To observe the distribution of polymorphism at sites -597 and -572 in IL-6 promoter region in Tibet Tibetan population and to provide the theoretical data for Tibetan population genetics and background of immunity.DESIGN: Randomized investigation.SETTING: Institute of Anthropology, Jinzhou Medical College.PARTICIPANTS: Totally 108 healthy Tibetan teenagers were selected from Lasa and Naqu region in Tibet autonomous region from October 2003 to July 2004, including 60 males and 48 females, aged from 14-21 years. Inclusive criteria:The parents of the volunteers were healthy Tibetans after body examination. The volunteers knew the fact, agreed to participate into the trail and signed the informed consent.METHODS: 5 mL peripheral vein blood was collected from 108 Tibetan teenagers. DNA from human leucocytes was extracted by salt fractionation. IL-6 promoter including -597 and -572 fragments was amplified by polymerase chain reaction (PCR). Representative fragments were cloned then sequenced after restriction fragment length polymorphism (RFLP).MAIN OUTCOME MEASURES: Distribution of polymorphism in Tibet Tibetan population; Results after comparison with those of other nationalities including Han population.RESULTS: Data of 108 Tibetan teenagers were involved in the result analysis. ①Distribution of polymorphism on -572C/G site of IL-6 promoters in population of either sex: There were no GA and AA genotypes at site -597, but only GG genotype appeared. There were CC, CG and GG genotypes at site -572, and the frequencies were 0.63, 0.35 and 0.02 in order. Distribution of genotype with representativeness met the Hardy-Weinberg equilibrium. Allele frequencies were 0.81 and 0.19, respectively. There was no significant difference of either sex in genotype and allele frequency (P ＞ 0.05). ②Distribution of polymorphism on -597 G/A and -572 C/G in different nationalities: GG, GA, AA genotypes appeared on -597 site in England and France, and G and A allele frequencies were 0.60 and 0.40,respectively. It was significantly different from that of Tibetan in Tibet. Furthermore, Japanese had no polymorphism,which was similar to that of Hans in China (P ＞ 0.05). ③Genotype of different straps and results of DNA sequencing:Only GG genotype was found on -597 site (without the restriction site, one fragment after restriction, PCR amplification products), no GA and AA genotypes. CC, CG and GG genotypes appeared at site -572, and frequencies were 0.64,0.35 and 0.01, respectively. Distribution of genotype with representativeness met the Hardy-Weinberg equilibrium (P ＞0.05). Allele frequencies were 0.81 and 0.19, respectively. There was no significant difference of either sex in genotype and allele frequency. Distribution of gene frequency and allele frequency in IL-6 were similar between Tibetan and that of Hans, but it was significantly different from that of population in England, France and America.CONCLUSION: There are nationality differences of IL-6 gene polymorphism at sites -597 and -572. No polymorphism is found at site -597 in Tibetan. Race differences are seen at site -572, having CC, CG and GG genotypes and G allele is rate. Compared with white population, there is significant difference in genotype and allele frequency at site -572. Their characteristics are close to Hah population and Japanese, which may be associated with genetic gene of persons living in plateau.