Tyrone Thwaites

Familial Hypercholesterolemia is a relatively common genetic disease

Familial Hypercholesterolemia is a relatively common genetic disease, though it can be very serious. It is the most common form of inherited high cholesterol levels, and depending upon its genetic transmission, can range from incredibly severe, to a manageable disease. According to Genetic Home Reference (2007) , the rate of the disease is approximately one in five hundred people (1/500), and that its appearance depends on a combination of both genetic and environmental factors.

The genetic basis of familial hypercholesterolemia is quite complex, though can be explained simply enough to be able to make a comparison with normal regulation of plasma cholesterol levels. Essentially, familial hypercholesterolemia occurs as a result of a mutation on the LDLR gene, which allows the low-density lipoprotein receptors to be made. The role of these receptors is to regulate the amount of cholesterol in the blood. Some mutations cause these receptors to be decreased in number, or alter the ability of the receptors to remove lipoproteins from the blood. Therefore, such mutations cause excess levels of cholesterol in the blood.

The cause of such mutations are not merely a random event, but a result of transference of the defective gene from parents of the affected. This particular disease is autosomal dominant, meaning it can be transferred from either parent, and requires only one defective allele to be present. Similarly, it is possible for both defective alleles to be passed on from the parents of the individual, and this often results in a more severe case of the disease.

In a regular, unaffected individual, the gene LDLR initiates the regulation of plasma cholesterol levels. The gene prescribes the creation of low-density lipoprotein receptors, which attaches to particles known as low-density lipoproteins. The gene is a part of chromosome 19, and generally clears cholesterol of the blood so that it is at a regular level. This occurs by the receptors binding to the lipoproteins and removing them from the blood. Though when a defect occurs on the LDLR gene, the removal of the lipoproteins by the receptors is inhibited. Hence there is a great increase in levels of cholesterol in the blood, and according to Medline Plus (2008) , can result in obesity, cholesterol deposits in the eyelids, and cholesterol rich skin deposits. Hence, these effects result in the stiffening of arteries, increased blood pressure, and the greater risk of a blockage in the transmission of blood to the heart. Therefore, indicating how this gene can cause heart disease.

There are many possible treatments for the disease familial hypercholesterolemia. These include both drastic lifestyle changes, and the use of drugs. The form of treatment that is most successful depends on which form of the disease has been inherited. Heterozygous forms of the disease (only one defective allele inherited) normally respond well to diets that reduce the intake of fats, and bring lipid levels down to a reasonable level. This works by limiting the intake of fats, that would normally contribute to cholesterol levels. Hence a reduced intake, means that less fatty deposits will be found in arteries and other areas of the human body. Therefore reducing the risk of heart disease or a heart attack. Although a direct lifestyle change through exercise and diet appears the most obvious treatment, this is not necessarily the case with the homozygous form of the disease being a poor respondent to lifestyle change. Such patients generally cannot alter the effects of the disease through a better choice of diet, as their levels are generally to high, and the cholesterol re-forms in deposits too quickly for exercise or diet to wear off. The other alternative for treatment, and generally as a last alternative, is the use of prescribed drugs. According to the University of Maryland Medical centre (2008) , some successful drugs include bile acid sequestrant resins, Fenofibrate, Gemfibrozil, Nicotinic acid, and Statin drugs. Most drugs act in a way as to increase the amount of lipoprotein in the blood, which in turn attaches to receptors, and in turn reduces the level of cholesterol in the blood. Sometimes, even drugs are not effective in homozygous individuals. So a liver transplant or LDL removal techniques are often applied as drastic measures to reduce the severity of the disease.

Often, individuals can be diagnosed with the disease, yet never suffer a heart attack. This depends on the form of the disease that they have, either homozygous or heterozygous. Those with the heterozygous form may never have massive amounts of cholesterol deposits in their body, and hence they may not ever suffer a heart attack. Though homozygous individuals almost always have very large cholesterol deposits throughout their body, and this dramatically increases the chance of coronary heart disease, and hence a heart attack. Sometimes, deposits can form on parts of the body such as the Achilles tendon, and not as severely in arteries, hence the chance of heart attack is minimised, though the increase in mobility problems becomes a problem.

Familial Hypercholesterolemia is a disease that can be very severe and cause many problems for an individual or family. Understanding it's genetic basis, symptoms and treatment can be the first step towards establishing greater awareness of such a disease in the community.

References

Batzel, J and Kappel, F. (2007). Cardiovascular and Respiratory Systems- Modelling, analysis and control. Published by Frontiers in applied mathematics.
Gustafson, A. (1979). Plasma Lipoproteins Plasma Proteins, pg 89.
Author Unknown, (2007). Genetics Home Reference- Hypercholesterolemia. [INTERNET] AVAILABLE FROM: http://ghr.nlm.nih.gov/condition=hypercholesterolemia
Author Unknown, (2008). University of Maryland Medical Centre- Familial Hypercholesterolemia Treatment. [INTERNET] AVAILABLE FROM: http://www.umm.edu/ency/article/000392trt.htm
Zieve, D. (2008). Medline Plus- Familial Hypercholesterolemia [INTERNET] AVAILABLE FROM: http://www.nlm.nih.gov/MEDLINEPLUS/ency/article/000392.htm

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