Genetic determinism and probabilism

170px-DNA_orbit_animated_static_thumbThe New York Times has a piece up, I Had My DNA Picture Taken, With Varying Results, which begins:

I like to plan ahead; that much I knew about myself before I plunged into exploring my genetic code. I’m a healthy 28-year-old woman, but some nasty diseases run in my family: coronary heart disease, rheumatoid arthritis, Alzheimer’s and breast cancer.

So I decided to read the tea leaves of my DNA. I reasoned that it was worth learning painful information if it might help me avert future illness.

The author is a masters student in bioethics at Columbia (of curious note, her father is the designated heir of Ayn Rand and high priest of mainline Objectivism), so not the typical person off the street. That being said, the piece does reflect implicitly the almost oracular powers conferred to genetic data in the imaginings of the public. It is totally understandable, if somewhat concerning, that direct-to-consumer firms differ in their assessments. Even if the author had obtained a very high quality whole genome sequence, and had a large population sample to compare it against in terms of traits and genotypes, there’s only so much predictiveness you can squeeze out of complex traits. This does not mean that understanding the genetic underpinnings of diseases is without utility. Simply that there are limits to the confidence of predictions of common and complex diseases in the case of one particular individual. In fact, even if you are healthy, have no family history, and exercise, you can die of a heart attack in your 50s.

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