Heritability in Cancer

Recently we have looked into the role of heritability in cancers. There have been many studies looking into to this and most have returned similar results. One study done by Kari Hemminki and colleagues found that genetic heritability contributed anywhere from 10-14% in the cancers studied. Another study by Paul Lichtenstein also concluded that inherited genetic factors make a minor contribution to the susceptibility of most neoplasms. This indicates that the environment has the principal role in causing sporadic cancer. Based on these studies I would estimate that the heritability factor of cancer is fairly low. Also because it is so low, selection would not have a major influence on the disease as there is not much to select for. Similarly the effects of inbreeding would also be minimal. However, in certain cases where inheritance does play a role, inbreeding could increase the probability of passing those genes on as it would also increase there exposure to selection.

Reflection (Steve)

This project has also taught me a lot about the practical applications of evolution. Until this class and mainly this project I never thought about evolution being relevant to things such as disease today. Through the papers I also learned a lot about the p53 gene and cancer in general. I was completely unaware of the p53 gene family before reading these papers. Similar to the other members of my group I did not know that there was such a complex family of genes that regulated cell apotosis. I thought that there were simply environmental triggers that caused a certain cell to begin the process of cell death. Another thing that was surprising to me was how genetically predisposed some can be to cancer. I always knew that there was some hereditary effect, but I thought that for the most part the majority of cancer cases were due to mutations caused mainly by genetic error or environmental influences. This project has been enlightening in many ways and has been a worthwhile experience.

Why doctors need to know about evolution

For us, there is one reason that stands out above the others as to why doctors need to have a working knowledge of evolution. We feel that a very big problem in the medical field today is bacterial resistence to drugs. If a doctor does not know about evolution, he or she could easily prescribe antibiotics to every patient that shows symptoms of a bacterial infection. Presumably, these doctors would prescribe the same drug repeatedly to every patient they encounter. The reason that this is a problem is that bacteria can build resistence to drugs that are over prescribed. As we learned in evolution class, the antibiotics will put a pressure on the bacteria. Only the bacteria that, by random chance, have the ability to withstand the antibiotic, will survive and reproduce. The selection for these resistant bacteria will allow them to thrive while the bacteria which are not resistant will fall victim to the drugs. As all of the non-resistant bacteria are eliminated, only the resistant ones will remain, leading to a completely resistant strain of bacteria.

A perfect example of this kind of selection leading to resistant bacteria is with Staphylococcus aureus. The over-prescription and misuse of the antibiotic Vancomycin has led to a resistant strain of S. aureus. If doctors have a working knowledge of evolution, they will understand that the selective pressure on bacteria from antibiotics will lead to such a situation. With this knowledge, they will hopefully restrain the use of antibiotics to the cases that absolutely need them, or at least use a variety of antibiotics. It is also important that doctors know about evolution like this so they can better inform their patients about the importance of following the regimen for antibiotic use. If a patient stops using the prescribed drug too soon, only the strongest bacteria will be left and able to multiply. Because of Vancomycin-resistant Staphylococcus aureus and other drug-resistant bacteria, we feel that doctors must understand both the mechanisms and effects of evolution.

What I have learned from this project thus far (Rick)

This project has taught me quite a bit so far about a practical use of evolution. While many are discussed in class, having to research a topic that relates to diseases that people we know have helps me to put my classroom knowledge to more use. From the papers I read for this project about p53 mutations and how that affects cancer, I have learned several things. First of all, I have never learned about the moleuclar nature of cancer before reading these articles. Just like Connor, I always thought cancer just happened when cells were not able to undergo apoptosis. Through reading about p53, I have learned that gene duplication, and subsequent mutations on the duplicated genes, allows for the creation of a gene family. When all of the genes in the gene family are selected for in such a way that they work together in harmony, it is necessary that all are expressed perfectly to allow the cells to function properly. In the case of p53, mutations and misfoldings cause at least one of the genes in the p53 gene family to not function properly which prevents apoptosis. For me, learning that mutations like this inhibit apoptosis gives me a small understanding of what can cause cancer. Studying the evolution that allows the genes in the gene family to arise through gene duplication has allowed me to fully understand exactly what happens. This kind of supporting knowledge allows me to have a better grasp on p53 and its ability to promote cancer. I have thoroughly enjoyed having the opportunity to build my knowledge of this protein family while putting my evolution knowledge to practical use.

What I learned (Connor)

I learned from the papers about how much evolution can affect cancer. I learned how much of an effect p53 has on whether cancer will develop to a stage that is terminal or not, and I also learned that p53 can determine whether an individual will even develop cancer at all. I learned that cancer is regulated to some extent by a gene (p53) and until now I had never known that there was a gene responsible for preventing the uncontrollable duplication of cells. I thought that cancer was as simple as a cell being unable to stop duplicating itself, but now I have an appreciation for the fact that it is a much more complicated phenomenon and this fact makes me realize that cancer is even more dangerous than I had previously thought. This seems to explain to me why a cure for it has eluded the hard working scientific community for so many years.