Age- and gender-specific epistasis between ADA and TNF-α influences human life-expectancy

Aging is a complex phenotype with multiple determinants but a strong genetic component significantly impacts on survival to extreme ages. The dysregulation of immune responses occurring with increasing age is believed to contribute to human morbidity and mortality. Conversely, some genetic determinants of successful aging might reside in those polymorphisms for the immune system genes regulating immune responses. Here we examined the main effects of single loci and multi-locus interactions to test the hypothesis that the adenosine deaminase (ADA) and tumor necrosis factor alpha (TNF-α) genes may influence human life-expectancy. ADA (22G>A, rs73598374) and TNF-α (-308G>A, rs1800629; -238G>A, rs361525) functional SNPs have been determined for 1071 unrelated healthy individuals from Central Italy (18-106 years old) divided into three gender-specific age classes defined according to demographic information and accounting for the different survivals between sexes: for men (women), the first class consists of individuals<66 years old (<73 years old), the second class of individuals 66-88 years old (73-91 years old), and the third class of individuals>88 years old (>91 years old). Single-locus analysis showed that only ADA 22G>A is significantly associated with human life-expectancy in males (comparison 1 (age class 2 vs. age class 1), O.R. 1.943, P=0.036; comparison 2 (age class 3 vs. age class 2), O.R. 0.320, P=0.0056). Age- and gender-specific patterns of epistasis between ADA and TNF-α were found using Generalized Multifactor Dimensionality Reduction (GMDR). In comparison 1, a significant two-loci interaction occurs in females between ADA 22G>A and TNF-α -238G>A (Sign Test P=0.011). In comparison 2, both two-loci and three-loci interaction are significant associated with increased life-expectancy over 88 years in males. In conclusion, we report that a combination of functional SNPs within ADA and TNF-α genes can influence life-expectancy in a gender-specific manner and that males and females follow different pathways to attain longevity.