Dong Jo Kim, Sang Mi Yi, Seung Yeon Lee, Heun Soo Kang, Yoon-Ho Choi, Yeong Wook Song, and Sang Chul Park. Association between the MLH1 gene and longevity. Received: 21 July 2005 / Accepted: 17 January 2006 / Published online: 11 February 2006. Springer-Verlag 2006.

Abstract:
Perturbations in genomic stability result in cancer, reduced lifespan, and premature aging. MLH1 is a mismatch repair enzyme that acts to maintain genomic stability. A loss of MLH1 increases cancer incidence and apoptosis resistance, suggesting a link between MLH1 and longevity. We found that MLH1 is associated with longevity by comparing a centenarian group with a control group. Our data indicate a critical role for MLH1 in longevity.

MLH1 is one of the critical genes that maintain genome stability, and its functional shortcomings are strongly associated with human colon cancer. Loss of the MLH1 gene results in microsatellite instability, which is a hallmark of cancer and may be central to the mechanism of cancer development. MLH1-deficient mice are prone to cancer development (Prolla et al., 1998). These phenotypes are similar to those typically encountered in aged humans. In addition, MLH1-deficient cells show resistance to the apoptosis induced by DNA damaging agents, consistent with evidence of a decline in apoptotic response during aging (Hardman et al., 2001). Recently, it was demonstrated that mutations throughout the entire coding regions of MLH1 are predominantly inactivating and eliminate the effect of wild-type MLH1 in proliferating cells (Shcherbakova and Kunkel, 1999; Pang et al., 1997). Therefore, we hypothesized that polymorphisms of MLH1 influence genomic stability and thereby lifespan. To examine this hypothesis, we analyzed the entire coding region of the MLH1 gene in 85 Korean centenarians and in 106 Korean controls using two-dimensional gene scanning. Two-dimensional gene scanning (TDGS) is a method of mutation detection based on the electrophoretic separation of PCR-amplified DNA fragments based on size in the first dimension and on base sequence in the second dimension (Dhanda et al., 1998). We identified nine single nucleotide variants of MLH1 in two population groups. We focused on three SNPs in a coding sequence leading to an amino acid substitution because cSNPs play important roles in the function of protein MLH1 (C670T; Arg217Cys, A676G; Ile219Val, T1172A; Val384Asp). The distributions of all three SNPs were in Hardy-Weinberg equilibrium (HWE: P>0.05, data not shown). Analyses of all genotype and haplotype associations with longevity were performed using logistic regression models after adjusting for the confounding effects of gender caused by differences in ascertainment.

Table 1 Effect of MLH1 haplotype on longevity

Centenarians Controls P value AORa 95% CI Age 102.33 ± 2.59b 56.24 ± 10.67b <0.0001c Gender (%) Male Female Male Female 14(16.47) 71(83.53) 49(46.23) 57(53.77) <0.0001d Haplotypee CAT 13(92.86) 67(94.37) 39(79.59) 47(82.46) 0.0206 3.507 1.213,10.14 Others 1(7.14) 4(5.63) 10(20.41) 10(17.55) 

bMeans and standard deviations
cT-test on the two groups
dChi-squared test on the two groups
eHaplotype frequencies and individual haplotypes were generated using the Expectation Maximization (EM) algorithm, which reconstructs individual probabilities for individual phasing accuracy based on unphased genotype data, as well as estimates on the overall haplotype frequencies and their standard errors.

Marginally significant allelic association was detected only between polymorphism at position 1172 and longevity by a dominant model (P=0.0443, adjusted odds ratio (AOR)=0.199, 95% confidence interval (CI): 0.04-1.96). According to our hypothesis, we further compared the frequencies of MLH1 haplotypes in the centenarian and control groups under a recessive model. To avoid misleading results caused by rare haplotypes, we analyzed all haplotypes with a frequency greater than or equal to 5% in both the centenarians and the