Is the -174 C/G polymorphism of the IL6 gene associated with elite power performance? A replication study with two different Caucasian cohorts.

A functional -174 C/G polymorphism in the interleukin-6 gene (IL6) is a candidate to explain individual variations in exercise-related phenotypes. To replicate recent findings showing an association between the G allele and GG genotype of elite power sports performance in European (Spanish) Caucasian males, we compared allelic and genotypic frequencies of the IL6 -174 C/G polymorphism among elite endurance athletes (n = 74) and power athletes (n = 81) and non-athletic control subjects (n = 205) of both sexes from Israel. All subjects were Israeli Caucasians (with an equivalent ratio of non-Ashkenazi and Ashkenazi descent in each group; 2:1). We found no differences in the genotype or allele frequencies among groups (all P > 0.3). We further compared the genotype and allele frequencies between national- (n = 109) and international-level Israeli athletes (n = 46) in the endurance and power group, and found no significant genotype or allele differences after adjusting for multiple comparisons. We repeated all the analyses after pooling the Israeli and Spanish control subjects, endurance and power elite athletes, and found no genotypic and allelic differences among groups. The results did not change when the analyses were repeated including only the best Israeli athletes (i.e. the international-level group) together with the group of elite Spanish athletes (P > 0.2). In conclusion, the results of the present study did not show an association between the G allele of the IL6 -174 G/C polymorphism and power sports performance in the Israeli (Caucasian) population. Our findings support the need to replicate association results between genetic polymorphisms and athletic status in populations of different ethnic backgrounds with the largest possible population samples.