Age-related Macular Degeneration (AMD) is defined as the "deterioration or breakdown of the eye's macula". The macula, is a small part of the retina that is responsible for what is called the "central-vision" or the part of vision that allows you to see very fine details more clearly. The macula allows you to do things such as thread a needle, read a street sign, or read a book, so when a person develops macular degeneration actions such as these can be hindered.
Age-related macular degeneration is caused by the natural aging process, but the risk can be increased by both genetic and environmental factors. The symptoms of the disease include things such as: blurriness, dark areas or distortion in your central vision, and perhaps permanent loss of your central vision. With this disease, the symptoms will generally only affect the patient's central vision, so peripheral vision is not affected. To help illustrate this notion, view the picture of the clock to the right, which is what a person affected by age-related macular degeneration would see. There are two types of macular degeneration which are called dry AMD and wet AMD. Follow the links to learn more about the two types of AMD. There is a 45-71% heritability connection with AMD, which means that 45-71% of the casue of the disease has to do with the person's genetics.
Genetic Significance: Edit
When it comes to AMD, there are 5 main markers that geneticists will look for in order to assess the person's risk for developing the disease. The 5 markers are: SNP rs1061147 on the CFH gene, SNP rs547154 on the C2 gene, SNP rs3750847 on the LOC387715/ARMS2 gene, SNP rs2230199 on the C3 gene, and SNP rs9621532 on the TIMP3 gene. If a specific genotype of all of these SNP's on these different genes are present, there will be an increased risk of that person developing AMD. For the patient pictured on the right for example, his odds for developing AMD are increased 2.76x by the CFH marker, 1.07x by the C2 marker, 1.62x by the LOC387715/ARMS2 marker, 2.38x by the C3 marker, and 0x by the TIMP3 marker.
These markers and SNP's are related to developing AMD because if a person has a specific genotype at one or more of these SNP's within their DNA, they are at increased risk of developing AMD. If the more risky form of the SNP rs1061147 is present, the person will make a different form of the CFH gene and this leads to reduced ability to bind CRP, which could lead to a hyperactive complement system that damages eye tissue. The second SNP (rs547154) also has to do with the complement system, but it is not widely understood yet. The third SNP (rs3750847) is known to have function within mitochondria, but also is not widely understood. The SNP rs2230199 is also a part of the complement system because it codes for the C3 protein, which when cleaved, plays a large role in the complement system. Finally, the SNP rs9621532 is associated with the degradation of extracellular matrix and communication between nerve cells, both of which can lead to AMD if not properly operating.
The results of the genetic testing (of the person previously used as an example) in regards to the genotypes in relation to developing AMD, puts him at a 44.3% risk of developing AMD between the ages 43 and 79, compared the average risk of 6.5% between the ages of 43 and 79. This is due to his genetic make-up and is mostly heriditary. The genotype is the basis for the variation in phenotype and in this case, the genotype is what is predicted to cause the faulty phenotype associated with developing AMD.
Although there is no known cure for AMD, there are a few treatments that are available to decrease the amount of vision loss and/or prolong the onset/development of the disease. The treatments include, but are not limited to: anti-angiogenic drugs, laser therapy, photodynamic laser therapy, vitamins, and low vision aids. Anti-angiogenic drugs prevent the growth and development of new blood vessels and prevents leakage from abnormal ones. Both laser therapy and photodynamic laser therapy are treatments that utilize lasers to damage the abnormal blood vessels casuing the affects of AMD. Vitamins have been shown to decrease the amount of vision loss associated with the degenerative activity of AMD, and low vision aids can be used to increase vision within the eyes of people struggling with AMD. As previosuly stated, all of these treatments don't get rid of the disease, but rather slow/decrease its affects.
1. What Is Age-Related Macular Degeneration? by www.geteyesmart.org
3. Age-Related Macular Degeneration Treatment by www.webmd.com
4. Lung Cancer by www.medicinenet.com