>Uric acid wGRS was not associated with fasting serum glucose, HbA1C, waist circumference, or BMI. On the other hand, waist circumference was causally associated with all the components of MetS including uric acid.
Here's what's happening: some genes are known to be associated with elevated uric acid. Other genes are known to be associated with increased waist circumference. Because several different genes are considered, it is assumed that the "side-effects" of these genes can be neglected; the failure of this assumption is called horizontal pleiotropy, and I don't feel confident assessing their methods on this point. MR is generally considered to provide a better degree of causality estimation than longitudinal data, because the genetic factors can be considered "prior" to other effects.
The authors find that the genes associated with uric acid are associated with worse cardiovascular symptoms, while they are not associated with other symptoms of metabolic syndrome; waist circumference genes are associated with all of the symptoms of metabolic syndrome. Also, the effect of weight circumference genes on uric acid levels is significant, while the effect of uric acid genes on waist circumference is not (a strange asymmetry, but I guess it makes sense).
So what the study really shows is that elevated uric acid appears to contribute to worse blood parameters. However, it doesn't contribute much to central adiposity.
> About ten million years ago, the common ancestor of apes and humans got a mutation that broke uricase, causing uric acid levels to rise. The mutation spread very quickly, suggesting that evolution _really_ wanted primates to have lots of uric acid for some reason. Since discovering this, scientists have been trying to figure out exactly what that reason was, with most people thinking it’s probably an antioxidant or neuroprotectant or something else helpful if you’re trying to evolve giant brains.
[1] https://slatestarcodex.com/2020/04/27/give-yourself-gout-for...
Or might make your flesh pungent and not tasty to predators. The 'stinkiest' fish in the world[1] has high levels of urea (so high that its toxic, and while not uric acid these two molecules are related and both are options in metabolic pathways for processing ammonia) and before eating, hákarl needs to be dried in ice sheds in the artic circle for 3 months. Even then it's acquired taste.
Still, it seems unlikely primates were hunted by some unknown predator in such large numbers, for evolution to select for those with slightly more pungent flesh to deter such predation, but ... who knows? :P ;) xx