Friday, October 31, 2008

Evolutionary perspective on the genetics of osteoporosis

This review paper in Human Genetics discusses osteoporosis from an evolutionary and genetic perspective, and sometimes reads like a list of personal health guidelines (which is ok, I guess). I'm usually pretty reserved when it comes to criticizing papers on my blog, but I'm going to make an exception and say that this paper was somewhat disappointing, especially given that it was published in a high level journal: Human Genetics.
Ok, so first the obligatory point about how we are "stone age bodies living in a novel, modern world":
" ... current demographic trends will have the effect of altering what was once a positive adaptation for distinctive human bipedality into a serious set of “collateral” pathology among the modern elderly (Latimer 2005)."
...then a brief mention on the source of population differences: (I don't like the "Africans" generalization)
"Therefore, Africans more frequently have lactose intolerance, probably because they do not need as much vitamin D and calcium to maintain their (relatively strong) skeletons. On the contrary, skin depigmentation and high consumption of dairy products do not seem to protect Northern Europeans from fractures."
They also go on to explain the mechanism by which consumption of whole grain and milk products likely aggravates the risk of osteoporosis, which is pretty interesting.

He then briefly moves on to the genetics of osteoporosis with this statement which I find a bit hard to swallow, maybe just because I'm a too much of a hard-core adaptationist:
"It seems accurate to assume that if osteoporosis has a genetic determinant, its genetics will share peculiarity with the aging per se, being an example of “post-reproductive” genetics (Capri et al. 2008), which is difficult to explain by a selection process."
He argues that there would have been no selection against osteoporotic phenotypes since these cause problems later in life and would have no effect early in life, an argument which leaves me unconvinced:
"Therefore, children with a “pro-osteoporotic” bone architecture and lower bone mineralization were not selected against—which means, they were able to transfer their genes further on."
At the end of the paper are statements about the future of evolution in humans (which generally make me cringe):
"Is natural selection still a driving force in humans, given that our survival is often less dependent on genes than on technology?"
Osteoporosis: an evolutionary perspective
David Karasik
Human Genetics early online
Abstract: Increased life expectancy has led to an overall aging of the population and greater numbers of elderly people. Therefore, the number of people with osteoporosis has increased substantially, accompanied with an epidemic of hip fractures. Osteoporosis is an age-related systemic condition that naturally occurs, among mammals, only in humans. Osteoporosis is known to be highly heritable. However, assuming a genetic determinant for this post-reproductive disease to be transmitted from one generation to the next is counter-intuitive, based on the principles of human evolution, I will attempt to provide an explanation of the phenomenon from the point of view of evolution, selection, and changed environment in humans, which contributed to human longevity, while on other hand, contribute to diseases of civilization, including osteoporosis. There is a need to delve into evolution of human species in search for adaptive patterns to a specific environment that humans are operating in the last couple of millennia, to clarify whether “good” and “bad” genes exist, and how to find and correct them. The answer to the above questions will help us to identify causes of the current epidemic of osteoporosis and to pin-point a tailored treatment.


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