Pack/year is defined as the number of cigarettes smoked per day multiplied by the number of years the person has smoked. a Smoking history was unknown for 1 elderly tumor-free woman.

Table 2

Depletion of heterozygous genotypes for CASP5 Ala90Thr polymorphism in elderly subjects.

Study groups Number of Observed Minor allele Expected number of p value for deviation from subjects (%) genotypes (%) frequency heterozygotes (%) Hardy–Weinberg equilibrium AA AG GG Elderly subjects Elderly tumor-free smokers (N/=75 years) 110 (100) 34 (31) 44 (40) 32 (29) 0.491 55 (50) 0.036 Elderly tumor-free women (N/= 75 years) 142 (100) 60 (42) 53 (37) 29 (20) 0.391 68 (48) 0.014 Elderly tumor-free subjects (N/= 85 years) 258 (100) 74 (29) 108 (42) 76 (29) 0.504 129 (50) 0.009 Total 510 (100) 168 (33) 205 (40) 137 (27) 0.470 254 (50) 0.000014 Comparison groups Lung cancer patients, young-onset and/or non-smokers 111 (100) 29 (26) 61 (55) 21 (19) 0.464 55 (50) 0.272 “High-risk” breast cancer patients 121 (100) 39 (32) 61 (50) 21 (17) 0.426 59 (49) 0.738 Middle-aged healthy subjects 549 (100) 153 (28) 270 (49) 126 (23) 0.475 274 (50) 0.743 Total 781 (100) 221 (28) 392 (50) 168 (22) 0.466 389 (50) 0.812

Noteworthy, middle-aged cancer patients and healthy donors demonstrated similar frequency of the Ala90Thr heterozygotes, therefore the association of this genotype with decreased survival cannot be explained by premature mortality from malignant disease. Possible impact of CASP5 polymorphism in other age-related maladies cannot be analyzed within our data sets, because only cancer-related status was documented with sufficient level of comprehension and reliability.

by Ivanova et al. (1998), who observed increased HLA homozygosity in aged subjects; however, other studies on HLA polymorphisms failed to provide evidence for the favorable impact of HLA homozygosity on life expectancy.

Ala90Thr polymorphism is located within the caspase recruitment domain (CARD) of caspase-5. This domain mediates interaction of caspase-5 with other proteins and is likely to influence the activity of this enzyme (Martinon and Tschopp, 2007). If alanine- and threonine- containing variants of caspase-5 have a somewhat distinct repertoire of interacting proteins, a combination of these alleles may render inflammatory responsiveness to a wider spectrum of stimuli. However, actual functional significance of CASP5 Ala90Thr polymor- phism remains unknown. Alanine and threonine have clearly distinct chemical properties: the former is a hydrophobic non-polar amino acid, while the latter is a polar hydrophilic molecule. The PANTHER (Protein Analysis Through Evolutionary Relationships) tool, which relies on multiple alignment of evolutionary and functionally related protein sequences, reveals that the Ala90Thr allelism may affect properties of caspase-5 (http://www.pantherdb.org/, Thomas et al., 2006). The PROTEUS2 analysis indicates that this substitution may result in the secondary structure change of the CARD domain (http:// wks16338.biology.ualberta.ca/proteus2/, Montgomerie et al., 2008). However, the SNPs3D web-based software suggests neutral signifi- cance of this SNP (http://www.snps3d.org/, Yue et al., 2006).

Previous investigations, including genome-wide association stud- ies, mainly focused on the discrimination between “favorable” and “unfavorable” gene variants, and rarely considered heterozygosity as the status with potentially specific phenotypic consequences. The presented above data look intriguing and certainly deserve validation in independent case-control series. If the significance of the CASP5 Ala90Thr heterozygosity is confirmed, functional properties of the CASP5 allelic variants need to be evaluated in laboratory assays. Furthermore, the role of CASP5 polymorphism in predisposition to autoimmune and inflammatory diseases has to be considered.

Acknowledgements

We cordially thank Prof. Vladimir Anisimov for stimulating discussions. The work is supported by the Russian Foundation for Basic Research (grants 07-04-91000, 07-04-00122 and 08-04-90105).

Table 3

Distribution of CASP5 Ala90Thr heterozygous genotypes according to gender and smoking status.

Study groups Number of subjects (%) Observed Minor allele Expected number of p value for deviation from genotypes (%) frequency heterozygotes (%) Hardy–Weinberg AA AG GG Elderly subjects Gender Males 19\6 (100) 58 (30) 74 (38) 64 (33) 0.515 98 (50) 0.0006 Females 314 (100) 110 (35) 131 (42) 73 (23) 0.441 155 (49) 0.006 Smoking status Smokers 165 (100) 53 (32) 59 (36) 53 (32) 0.500 83 (50) 0.0003 Non-smokers 344 (100) 115 (33) 145 (42) 84 (24) 0.455 171 (50) 0.005 Unknown 1 – 1 – – – – Comparison groups Gender Males 303 (100) 80 (26) 157 (52) 66 (22) 0.477 151 (50) 0.502 Females 478 (100) 141 (30) 235 (49) 102 (21) 0.459 237 (50) 0.824 Smoking status Smokers 421 (100) 117 (28) 220 (52) 84 (20) 0.461 209 (50) 0.289 Non-smokers 239 (100) 65 (27) 111 (46) 63 (26) 0.496 119 (50) 0.272 Unknown 121 (100) 39 (32) 61 (50) 21 (17) 0.426 59 (49) 0.732

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