So what is a SNP - a single nucleotide polymorphism - and why should you care? A quick definition:
A single nucleotide polymorphism (SNP, pronounced snip), is a DNA sequence variation occurring when a single nucleotide - A, T, C, or G - in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual). For example, two sequenced DNA fragments from different individuals, AAGCCTA to AAGCTTA, contain a difference in a single nucleotide. In this case we say that there are two alleles : C and T. Almost all common SNPs have only two alleles.
Remember that a single gene is thousands of nucleotides long; SNPs are tiny differences considered in that scheme. However, in the same way that researchers - against initial skepticism - have been turning up single gene mutations that cause longevity for some time now, the community is starting to build the case for single SNPs that confer longevity benefits.
A well known functional SNP in the tumor suppressor TP53 gene leads to increased longevity: in the Danish general population (n = 9219) homozygotes for the minor allele versus homozygotes for the major allele had an increase in median survival of 3 years. This is partly explained by increased survival after development of cancer or other diseases, in accordance with the observation that this Arg72Pro substitution in the p53 protein has important influence on cell death via increased apoptosis. Thus, the increased longevity may be due to a generally increased robustness after a diagnosis of any life-threatening disease.
In contrast to widespread skepticism on the importance of SNPs in humans, this gain-of-function p53 SNP of importance for cell repair mechanisms has a profound influence on longevity.
"Profound" here is in comparison to most examined SNPs, which appear to cause no meaningful differences. I imagine there will be other longevity SNPs uncovered in the future - there are tens of millions identified so far, and only a small fraction well studied. This particular SNP is another confirmation of the potential of p53 engineering for longevity:
p53-related engineering looks to have at least as much potential as therapies based on the biochemistry of calorie restriction - which is to say not so much potential if you're already old. This is all about slowing rates of aging, not repairing the damaging of aging. This is why I favor quite different approaches to the engineering of human longevity.