Diseases for Darwinism

This article discusses Huntington's disease, what causes it, and the other effects that having this disease can have besides the classic symptoms. Huntington's disease is a neurological disorder that destroys neurons in certain regions of the brain. This causes the patient to have difficulty controlling movements. This can lead to various cognitive and emotional problem. This disease occurs due to a mutation that leads to the abnormal elongation of a gene known as huntingtin. The length of this gene becomes problematic when it exceeds past a certain extent and the length has an impact on the severity of symptoms.

Animals with this type of mutation only develop Huntington's when they make p53 (the tumor suppressor we learned about in Chapter 14!). Studies at Tufts University have found that people with Huntington's disease are less likely to have cancer and have more children than the average person. It is possible that increased p53 plays a role in these "side effects" of Huntington's. This is because, as we have previously learned, p53 regulates cell division and helps prevent cancers. The article goes on to talk a little bit more about p53 and its link to Huntington's. However, I want to get more into the material that is related to Chapter 16. As we know, Chapter 16 is about simple patterns of inheritance. As we have also learned in class, Huntington's disease is autosomal dominant. Look at this nifty picture to see how this disease is passed down generations:

The mutated gene is located on an autosomal (non-sex) chromosome and a person needs only one copy of the mutated gene for them to express the disease. As you can see in the picture above, the father is heterozygous for Huntington's but expresses the disease since it is dominant. Because he has children with a normal woman, 50% of his kids are unaffected while the other 50% are affected. I retrieved this infromation from here. If you are curious about Huntington's this site is extremely reliable and has a brief overview of the disease as well as detailed explanations.

The information in the previous paragraph is mostly review (since we have discussed the autosomal dominant nature of Huntington's in class), and I would also like to discuss another aspect of the Scientific American article that relates to our current chapter. A biologist at Tufts, Philip Starks, who has been studying p53 and Huntington's (as mentioned before) suspects that Huntington's is an example of antagonistic pleiotropy. Pleiotropy is when a mutation in a single gene results in multiple effects on the individual's phenotype. There are several forms of pleiotropy. One is when a single gene expression can alter cell function in more than one way. Another is when different cell types express a gene within a multicellular organism. Finally, one gene may be expressed at different phases of development. Check out pg. 343 in our biology textbook for even more information regarding pleiotropy. Starks believes that Huntington's may be pleiotropic because the same protein that results in the debilitating symptoms of Huntington's may also be responsible for making Huntington's patients more reproductively successful.