Sunday, January 20, 2008

Evolution Giveth, Evolution Taketh Away..

This is a story of fickle evolution, cancer, fertility, and Huntington's disease. This story is real, and no names have been changed to protect the innocent.

Huntington's disease is a genetic disorder caused by an overly long repeating CAG stutter. The length of the stutter determines if you get the disease (35 repeats seems to be the threshold) and the severity of the resulting disease. This allele appears to be connected with the production of a protein called p53. p53 is a very important protein, it modulates when cells divide and die (apoptosis), when new blood vessels form, and it also appears to modulate the immune response. This link to p53 is very important because it is the key to why the mutation has not died out in the population. People with the Huntington's allele have a higher level of p53 in their blood. p53 increases the immune response, and it also reduces the incidence of cancer, probably by boosting the immune response to incipient cancers.

People with the Huntington's allele are about 125% more fertile than those who do not have the gene. It is unclear why but one hypothesis is that people with Huntington's are healthier during their childbearing years, and therefore have healthier pregnancies. p53 might have an effect on the reproductive system that has not been detected yet. And since the debilitating effects of Huntington's generally don't appear until the prime childbearing years (median diagnosis is at age 39, although it ranges from age 2 to age 82), the mutation can and does survive from generation to generation. Additionally, people with Huntington's develop depression and cognitive deficits in the early stages of their disease, so it is possible that a certain percentage of Huntington's patients may not be able to make good decisions about reproduction as well, leading to more pregnancies.


Anonymous Ride said...

That's an interesting article, but I'm not sure why you posted it. It does seem to me to be an argument FOR evolution.

I can tell you that my own father broke off an engagement with a young woman in his youth, because she carried a gene for birth defects.

He wanted a family, but was unwilling to risk bringing a child into the world with debilitating defects, thus he broke off his engagement.

I applaud his decision, and I admire the young woman for giving him forwarning of the potential consequences of her procreating.

Faced with the same choices, I wonder how many people would elect to remain childless? What a delimma.

Maybe someday advances in science will provide alternatives.....

January 21, 2008 9:27 AM  
Blogger Rorschach said...

Ride, I posted it because I found it interesting that such a genetic trait could be both beneficial and detrimental at the same time and in so many seemingly unconnected ways. I think we will find a great many things have such a Jekell/Hyde dichotomy in their evolutionary history.

I don't recall ever saying I disputed evolution in the least. If I did give that impression that was in error. I am not an intelligent design/creation theorist. I reject them completely as not even rising to the level of pseudoscience.

Too many people jump to the conclusion that all conservatives are bible thumping, close minded bigots. Just as many people (I must admit that I sometimes find myself stereotyping as well) jump to the conclusion that all liberals are secular communists, bent on removing every bit of morality, self-reliance, and personal responsibility from society. The reality is that there is a broad overlap on both ends of the political spectrum.

When I was much younger, I found myself contemplating a relationship with a woman with severe physical handicaps (seal limbed) that were passed down from mother to daughter but not to sons apparently, although they were carriers. She very much wanted a child. I did too, but I could not bring myself to bring a child into the world with such handicaps. She on the other hand, having lived it herself, saw it as no big deal.

January 21, 2008 10:00 AM  
Blogger Jean said...

Rorsc, I never meant to imply that you didn't believe in evolution! Sorry if my comment came across that way. (But I'm glad you know where I'm coming from. heh,heh)

I don't perceive myself as a conservative nor a liberal, though there are tenants on both sides that I can relate to.

Certainly, as we age, we hope we can see beyond "white and black," and acknowledge that there are "grey" areas that give rise to debate and contemplation.

I appreciate your blog, and I thank you for insights into matters I've never considered!



January 21, 2008 10:13 AM  

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