Methuselah's children

A note on that Boston University study of centenarian genetics: it may represent a rare case of a piece of research being slightly undersold in the popular press. The CBC (to take an example at random) reports:

In Thursday’s online issue of the journal Science, researchers say their model of 150 genetic variants helped to predict exceptional longevity—living to late 90s or longer—among people in the study compared with people in the general population of North America and Europe.

…The researchers identified a group of 150 genetic variants that they say can predict exceptional longevity with 77 per cent accuracy. …The team found 19 genetic “signatures” in the subjects’ DNA that were associated with diseases such as dementia and hypertension.

…To make their findings, the researchers compared disease-associated variants in 801 unrelated subjects enrolled in the New England Centenarian Study with 926 controls with the same Caucasian genetic backgrounds.

It would not be particularly impressive if the researchers built a model of “signatures” based on its 1,727-person sample and then found that the model explained 77% of the longevity within that same sample. After building the model they actually collected a whole new group, a “replication set”, of ethnically paired, mostly-Caucasian centenarians and non-centenarians. The model works as well on the “replication set” of oldies and controls as it does on the original “discovery set”; the individual components strongly associated with longevity in the original data are, overall, associated about as strongly amongst the new people. So the finding looks very strong, at least for Caucasians who have genetic backgrounds of the sort one might find in New England.

The authors of the study are excited about the possibility of their complex gene-hunting approach being adapted to questions about inheritable illnesses—and most of our biggest killers are, to a surprising degree, inherited. The same study could also just be done over for other ethnicities. At the same time, there’s a depressing deterministic quality to the outcome here. The genes that contribute most to extreme longevity don’t seem to be the ones that were previously known to be specifically connected to some disease.

It appears that the people who live to 100 and beyond don’t do so because they have strong genetic defences against stroke or Alzheimer’s or cancer, but because their overall aging clock is slower, and the diseases and disabilities to which they would otherwise be prone are all mutually delayed—in the wording of the study, “compressed”—into the tenth decade of life. More and more, one’s natural lifespan, as Bertrand Russell (1872-1970) joked, appears to depend on a careful choice of ancestors.

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