Genetics without the disclaimers

2 minute read

The NY Times covers a new genome-wide association study of SNP variants and response to exercise (“Is Fitness All in the Genes?”).

The phenotype is improvement in maximum oxygen consumption volume. Some people have rapid improvement with exercise and others don’t. Straightforward enough, and there is one SNP that accounted for 6 percent of the phenotypic variation, which is quite strong as far as these associations go. Usually GWAS associations explain a much smaller fraction of the phenotypic variance.

The final few paragraphs of the article irritated me. It’s like these stories have to follow a form, with a long disclaimer at the end. They report the facts – variant explains 6 percent of variation – and then they proceed to preach about how the facts may not matter:

It will be years, if ever, said Dr. Bouchard, before gene tests exist that can reliably separate high and low responders. Even if and when such tests become available, he continued, the results will not constitute an excuse for skipping workouts. There are countless other benefits provided by exercise, he said, apart from whether it raises your VO2 max. Exercise can reduce blood pressure and improve lipid profiles, he said. It can better your health, even if, by certain measures, it does not render you more aerobically fit.
More fundamentally, Dr. Bouchard said, elements of the interplay of genetics, environment, the human body and resolve probably always will remain mysterious and stubbornly individualized, no matter how much science disentangles the genome. People who dont have an ideal version of the ACLS1 gene to prompt aerobic improvements from exercise, for instance, might harbor a different, unidentified gene that just makes exercise feel enjoyable, regardless. So, too, might someone whose body is genetically predisposed not to respond aerobically to running blossom during weight training sessions.

Hello? Six percent of the variance is six percent of the variance. The article ought to just say that 94 percent of the variance is not explained by this SNP. That answers the question! That unadorned fact tells you that the SNP isn’t strongly predictive about exercise response for any single person. To do even better, the article ought to tell us how much of the total variance is explained by all the SNPs together.

I know, statistics can be difficult for NY Times readers, but honestly explaining the result would take a lot less space than what the article does do, which is to give us a long litany of “mysterious and stubbornly individualized.” And the “different, unidentified gene that just makes exercise feel enjoyable, regardless.”

Come on, people! Why not just tell us about earth spirits and auras?

The moralizing always goes the same direction. You’ll never hear hand-wringing about how we can’t trust exercise because it only predicts a small proportion of the overall variance in mortality risk. What about the “mysterious and stubbornly individualized” people who are healthy at 80 without ever lifting a barbell?