The most striking example comes from Japan. Here, there is a common variant in mitochondrial DNA, a change in a single DNA "letter". A decade ago Masashi Tanaka, now at the Tokyo Metropolitan Institute of Gerontology, and his colleagues reported that this tiny change almost halved the risk of being hospitalised for any age-related disease at all, while doubling the chance of living to 100. Most Japanese centenarians have the variant, but unfortunately for the rest of us it's very rare outside Japan.Note that Japan always comes out at or near the top of life expectancy rankings.
Of course, we have long known (or at least suspected) that genetics had something to do with longevity. But for national health statistics, what matters is distribution; if the distribution of longevity-improving genes were independent of national origin, then genetic effects would wash out in international comparisons. As this example demonstrates, that’s not the case.