Table 3 Chi square test results for the genotype distribution and allele frequencies of the 19- and 21-repeat alleles elderly and control groups.

All Women Men Elderly(%) Control(%) P value Elderly(%) Control(%) P value Elderly(%) Control(%) P value Genotype 19-repeat1 0.543 0.582 0.283 19/192 69(14.00) 70(16.47) 0.297 36(14.94) 33(14.80) 0.966 33(13.10) 37(18.32) 0.126 19/non2 242(49.09) 198(46.59) 0.45 126(52.28) 107(47.98) 0.355 116(46.03) 91(45.05) 0.835 non/non2 182(36.92) 157(36.94) 0.994 79(32.78) 83(37.22) 0.316 103(40.87) 74(36.63) 0.357 Allele 19-repeat3 380(38.54) 338(39.76) 0.592 198(41.08) 173(38.79) 0.477 182(36.11) 165(40.84) 0.145 non 606(61.46) 512(60.24) 284(58.92) 273(61.21) 322(63.89) 239(59.16) Genotype 21-repeat4 0.31 0.88 0.082 21/212 30(6.09) 33(7.76) 0.316 15(6.22) 16(7.17) 0.682 15(5.95) 17(8.42) 0.308 21/non2 200(40.57) 154(36.24) 0.179 94(39.00) 89(39.91) 0.842 106(42.06) 65(32.18) 0.0316 non/non2 263(53.35) 238(56.00) 0.421 132(54.77) 118(52.91) 0.688 131(51.98) 120(59.41) 0.114 Allele 21-repeat5 260(26.37) 220(25.88) 0.813 124(25.73) 121(27.13) 0.628 136(26.98) 99(24.50) 0.397 Non 726(73.63) 630(74.12) 358(74.27) 325(72.87) 368(73.02) 305(75.50)

1. P values were obtained by the chi-square test of whole genotype distribution categorized by 19-repeat allele. 2. P values were obtained by the chi-square test of genotype distribution categorized by each genotype. 3. P values were obtained by the chi-square test of allele frequencies categorized by 19-repeat allele. 4. P values were obtained by the chi-square test of whole genotype distribution categorized by 21-repeat allele. 5. P values were obtained by the chi-square test of allele frequencies categorized by 21-repeat allele. 6. After Bonferroni correction, p < 0.0017 is considered significant.

we found six genotypes which included one allele with 21 repeats: 17/21, 18/21, 19/21, 20/21, 21/22, and 21/23 (The number represents how many repeats there is in the microsatellite locus in this genotype). A chi square test showed a significant difference in the distribution of the 18/21 genotype in male elderly and male control p groups (11.11 vs. 5.45%, = 0.011; Table 4). After Bon- feronni correction for multiple tests, the result was no longer significant.

In a previous study of the same population [28], we reported no association between longevity and the three SNPs (rs2288377, rs5742612, and rs35767) surrounding the microsatellite. Combining the two datasets, we constructed the haplotype of each individual for the microsatellite locus and these three SNPs. The result is listed in Table 5. There are 18 different haplotypes in the population and no significant result was obtained in this study.

Discussion

Table 4 The comparison of genotypes with one 21-repeat allele in male elderly and male control groups

In the present study, we explored the association of a microsatellite polymorphism in IGF1 gene promoter with longevity in a Han Chinese population. The elderly and control groups were recruited from the same area. They shared the same living conditions, diet habits, and culture. This allows us to exclude non-genetic factors which may also affect longevity, and ensures that popu- lation stratification can be avoided to a certain extent in our study [29]. Additionally, the genotype distributions of both groups did not deviate from HWE.

Genotype Male Elderly(%1) Control(%1) P value2 173/21 14(5.56) 11(5.45) 0.716 18/21 28(11.11) 11(5.45) 0.0114 19/21 42(16.67) 34(16.83) 0.591 20/21 14(5.56) 7(3.47) 0.182 21/22 7(2.78) 2(0.99) 0.18 21/23 1(0.40) 0

To our knowledge, this is the first study of the corre- lation between this microsatellite polymorphism and longevity in a Han Chinese population. The allele distri- bution of this microsatellite in our population is consis- tent with a previous study on breast cancer in Chinese people [17]. The distribution is different from that in

Table 5 The comparison of haplotype distribution in elderly and control groups.

All Female Male Haplotype Elderly(%) Control(%) Elderly(%) Control(%) Elderly(%) Control(%) C 131 TT 1(0.10) 0 1(0.21) 0 0 0 C 16 TT 0 1(0.12) 0 1(0.23) 0 0 C 17 TT 78(7.99) 68(8.46) 37(7.71) 34(7.91) 41(8.27) 34(9.09) C 18 TT 162(16.59) 125(15.55) 74(15.42) 66(15.35) 88(17.74) 59(15.78) C 19 TT 357(36.58) 295(36.69) 186(38.75) 150(34.88) 171(34.48) 145(38.77) C 19 CA 1(0.10) 0 0 0 1(0.20) 0 C 20 TT 28(2.87) 21(2.61) 13(2.71) 12(2.79) 15(3.02) 9(2.41) C 21 TT 10(1.02) 8(1.00) 1(0.21) 3(0.70) 9(1.81) 5(1.34) T 18 CA 8(0.82) 3(0.37) 6(1.25) 2(0.47) 2(0.40) 1(0.27) T 19 TT 12(1.23) 8(1.00) 8(1.67) 5(1.16) 4(0.81) 3(0.80) T 19 CA 5(0.51) 16(1.99) 2(0.42) 11(2.56) 3(0.60) 5(1.34) T 20 TT 29(2.97) 22(2.74) 12(2.50) 12(2.79) 17(3.43) 10(2.67) T 20 CA 10(1.02) 7(0.87) 4(0.83) 3(0.70) 6(1.21) 4(1.07) T 21 TT 6(0.61) 10(1.24) 2(0.42) 8(1.86) 4(0.81) 2(0.53) T 21 CA 242(24.80) 186(23.13) 121(25.21) 103(23.95) 121(24.40) 83(22.19) T 22 CA 23(2.36) 28(3.48) 12(2.50) 15(3.49) 11(2.22) 13(3.48) T 23 CA 4(0.41) 4(0.50) 1(0.21) 4(0.93) 3(0.60) 0 T 24 CA 0 2(0.25) 0 1(0.23) 0 1(0.27) Total2 976 804 480 430 496 374 P-value 0.260 0.142 0.797

1. The number represents how many repeats there is in the microsatellite locus in this haplotype. 2. The total amounts are less than the whole numbers of the population individuals because there are missing data in SNPs

Caucasian population, as described by Jernstrom et al. [13], demonstrating that allele frequencies at this locus differ between the two populations. This difference may be caused by demographic geography and history of Chinese and Caucasian populations, or by genetic drift. However, within the Han population there is no signifi- cant difference in genotypes between elderly and control groups, even when stratified by gender. Our results sug- gest that no specific alleles at this locus are associated with longevity in this Han population.

Conclusions