What is Apo E? 
Apo E is a protein which, in the blood, helps carry cholesterol and fat. The three common forms of the gene for this protein are Apo E2, Apo E3, and Apo E4. In early 1993, Apo E4 was identified as a genetic risk factor for Alzheimer's disease.
The Apo E test is a lab test. Genetic material (DNA) is extracted from an individual's blood sample or cheek swap to assess the Apo E genes. A person inherits either an E2, E3, or E4 gene from each parent.
What is the normal function of the Apo E gene?
The Apo E gene provides instructions for making a protein called apolipoprotein E. This protein combines with fats (lipids) in the body to form molecules called lipoproteins. Lipoproteins are responsible for packaging cholesterol and other fats and carrying them through the bloodstream. Apolipoprotein E is a major component of a specific type of lipoprotein called very low-density lipoproteins (VLDLs). VLDLs remove excess cholesterol from the blood and carry it to the liver for processing. Maintaining normal levels of cholesterol is essential for the prevention of disorders that affect the heart and blood vessels (cardiovascular diseases), including heart attack and stroke.
There are at least three slightly different versions (alleles) of the Apo E gene. The major alleles are called e2, e3, and e4. The most common allele is e3, which is found in more than half of the general population.
How are changes in the Apo E gene related to health conditions?
Alzheimer disease -There is an increased risk with variations of the Apo E gene. The e4 version of the Apo E gene increases an individual's risk for developing late-onset Alzheimer disease. People who inherit one copy of the Apo E e4 allele have an increased chance of developing the disease; those who inherit two copies of the allele are at even greater risk. The Apo E e4 allele may also be associated with an earlier onset of memory loss and other symptoms.
It is important to note that people with the Apo E e4 allele inherit an increased risk of developing Alzheimer disease, not the disease itself. Not all people with Alzheimer disease have the Apo E e4 allele, and not all people who have this allele will develop the disease.
Other disorders associated with the Apo E gene -Variants of apolipoprotein E have been studied extensively as risk factors for many different conditions. For example, Apo E alleles have been shown to influence the risk of cardiovascular diseases. People who carry at least one copy of the Apo E e4 allele have an increased chance of developing atherosclerosis, which is an accumulation of fatty deposits and scar-like tissue in the lining of the arteries. This progressive narrowing of the arteries increases the risk of heart attack and stroke.
The Apo E e2 allele has been shown to greatly increase the risk of a rare condition called hyperlipoproteinemia type III. Most people with this disorder have two copies of the Apo E e2 allele, leading researchers to conclude that the e2 allele plays a critical role in the development of the condition. Hyperlipoproteinemia type III is characterized by increased blood levels of cholesterol, certain fats called triglycerides, and molecules called beta-very low-density lipoproteins (beta-VLDLs), which carry cholesterol and lipoproteins in the bloodstream. A buildup of cholesterol and other fatty materials can lead to the formation of small, yellow skin growths called xanthomas and the development of atherosclerosis.
Apo E variants have also been studied as a potential risk factor for age-related macular degeneration, an eye disease that is a leading cause of vision loss among older people worldwide. Some studies have suggested that having at least one copy of the Apo E e4 allele may help protect against this disease or delay the onset of vision loss, while having at least one copy of the Apo E e2 allele may increase the risk of this disease or cause symptoms to appear earlier. However, other studies have not found these associations. More research is needed to clarify what role, if any, Apo E variants play in the development of age-related macular degeneration. Recent studies suggest a role for Apo E in obesity and increased Body Mass Index (BMI) and blood lipid (fat) levels in obese children and in early onset Sjogren's Syndrome.
|
