Conclusions

In this study, no association was discovered between the microsatellite site in IGF1 gene promoter and longevity in a Han Chinese population. In males, the 18/21 geno- type was more frequent in the elderly group than in the control group (11.11 vs. 5.45%, p = 0.011). Future stu- dies including an increased sample size and more loci in the long haplotype block will enable us to test the hypothesized linkage between the 18/21 genotype and functional loci.

To explore the potential role of the microsatellite locus, we compared the genotype frequencies in elderly and control groups depending on 19-repeat and 21- repeat (the two most common alleles) to define categories. As stated in the introduction, the common 19-repeat allele is thought to be related to serum IGF1 levels and many age-related diseases, although the results are equivocal. The contradiction between studies can be explained by different population size, different ethnicities in different studies, and small effect of this polymorphism in complex diseases. Similarly, longevity is a complex trait, influenced by the additive effects of many genetic variations (not to mention stochasticity). Thus an association study may simply not have suffi- cient power to detect significant correlations between the 19-repeat and longevity.

Acknowledgements

We are grateful to the persons who participated in this research. In addition, we thank Dr. Hui Li, Dr. Cheng-ye Wang, Kristen Choffe and Christina Davy for their help in preparing the manuscript. We would like to acknowledge Shi-fang Wu, Shi-kang Gou, and Chun-ling Zhu for their help in experiments. This work was supported by National Basic Research Program of China (No. 2007CB507405), “Light in Western China” of the Chinese Academy of Sciences, the National Natural Science Foundation of China (30621092), and Bureau of Science and Technology of Yunnan Province.

Author details

1State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China. 2Laboratory for Conservation and Utilization of Bio-resource, Yunnan University, Kunming 650091, China. 3Graduate School of the Chinese Academy of Sciences, Beijing 100049, China. 4People’s Hospital of Dujiangyan City, Dujiangyan 611830, China. 5Dujiangyan Longevity Research Centre, Dujiangyan 611830, China.

Authors’ contributions

We initially found a significant difference between the 21-repeat/non genotype frequencies in male elderly (42.06%) and control (32.18%) groups, as well as between the 18/21 genotype (11.11 versus 5.45%, p = 0.011) and other genotypes. However, Bonferroni cor- p rections increased the values past the cut-off point for statistical significance. Based on these results, the 21- repeat can not be a potential functional allele for male longevity. The 18/21 genotype may still be linked to real functional variations, because in a recent study, a long haplotype block including this microsatellite region was reported [30]. We constructed haplotypes for each parti- cipant using our microsatellite and three SNPs data, and found that no single haplotype was positively associated with longevity. The haplotype block is long enough that more SNPs from this region could be included for test- ing if a potential functional site exists, and we recom- mend this approach be used before our initial hypothesis is fully rejected., in order to ensure that small sample size (of loci) did not bias the results.

LX and YPZ designed the research and wrote the manuscript. LX conducted the genotyping and statistical analysis. YG assisted in revising the manuscript. YG, SL, JY and LyX collected the blood samples. All authors read the paper and approved the final version.

Competing interests

The authors declare that they have no competing interests.

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