21…14…1…sounds more like the quarterback before the snap of the football, rather than the most important numbers you may ever hear. That’s right; chromosomes 21, 14, and 1 may contain single gene mutations that can strongly affect whether or not you develop FAD, or early onset familial Alzheimer’s disease. And that’s not all. Certain alleles (gene forms) associated with the apolipoprotein E (ApoE) genotype indicate a genetic risk factor for cardiovascular disease (CVD) as well.
Apolipoprotein E (ApoE) represents a class of proteins responsible for the metabolism of fats in the body.
Alzheimer’s Disease and Genetics
Alzheimer’s disease involves degraded connections between nerve cells within the brain, and the death of those cells. Amyloid plaques and tangles cause the debilitating symptoms of memory loss and confusion Alzheimer’s patients experience. In the case of early onset familial Alzheimer’s disease, individuals between the ages of 30 and 60 years old develop symptoms much earlier than other people.
The sticky plaques are formed in direct relation to the breakdown of APP (amyloid precursor protein). Single gene mutations found on chromosomes 24, 14, and 1 lead to this breakdown. Genetic studies help explain in part, why this form of Alzheimer’s disease exists at different stages of aging.
ApoE may indirectly affect the onset and progression of AD by modulating the cerebrovascular system function. ApoE4 may also contribute to neuro-degenerative processes in the brain as well.
ApoE testing may be instrumental in helping determine whether or not an individual will develop Alzheimer’s disease.
Cardiovascular Disease and the ApoE Gene
What is ApoE?
The ApoE gene provides a genetic blueprint for the production of a protein known as apolipoprotein E. The protein is essential to the body as it helps form lipoprotein molecules when combined with fats. Lipoprotein is necessary to transport cholesterol and other fats through the bloodstream.
Apolipoprotein E Genotyping
Located on chromosome 19 are three alleles (gene forms) that include e2, e3 and e4. Individuals who are born with at least one e4 allele are at increased risk for cardiovascular disease. This is because having an e4 allele links individuals to increased risk for low-density lipoprotein cholesterol that can be identified, even in childhood.
About 45% of the population has at least one high-risk variant within the ApoE gene. This may put those individuals at higher risk for coronary heart disease or stroke. Because the Apolipoprotein E gene plays an important role in certain metabolic processes (including metabolizing cholesterol and triglycerides) some people may be more predisposed to cardiovascular disease and less likely to respond favorably to statin therapies. Cholesterol levels must be properly managed to prevent heart-related conditions, heart attack, and stroke caused by blockages in the blood vessels and arteries.
Every year, more than 600,000 Americans die from heart disease, making it the number one cause of death in the nation.
Coronary heart disease is the most common form of heart disease, killing more than 370,000 people annually. Each year, about 735,000 Americans have a heart attack.
Aging and Cardiovascular Disease
High blood pressure, heart disease, and stroke are four times more likely in individuals over age 65, as compared to adults 18-64 years old. Research involving the impact of ApoE genotypes on cardiovascular disease in the elderly, reveals a complex relationship between age, lifestyle, environment and genetics. The ApoE genotype negatively affects lipids and inflammation, two major components in cardiovascular disease. These can be linked to both atherosclerosis and hypertension in individuals. Due to aging in general, correlations may be altered in the elderly population, however.
How does ApoE testing help?
ApoE genotyping can help health practitioners more effectively manage treatment involving elevated lipids. While no test is definitive, genotyping may aid in predicting whether or not an individual will possibly develop Alzheimer’s disease, or be responsive to statin therapies, designed to lower cholesterol in the blood.
Who can benefit from ApoE genotyping tests?
The ApoE gene is broken down into alleles known as e2, e3, and e4. More than half of the general population has the e3 allele.
Individuals who have high cholesterol or triglyceride levels, and who do not respond to diet and exercise regimens to naturally lower levels may benefit from this type of testing. Others who have family members with known ApoE e2/e2 genes can determine if they are at increased risk for early heart disease.
A health practitioner may request ApoE genotyping tests for these reasons.
What Test Results Mean—ApoE Alleles and Health
Individuals with ApoE e2/e2 alleles generally have lower LDL-C levels and higher triglycerides. ApoE e2 may also be linked to III hyperlipoproteinemia/hyperlipidemia, a rare genetic disorder affecting the metabolism of lipids. ApoE e2 is quite rare and may protect against Alzheimer’s disease. If Alzheimer’s disease develops in an individual with this allele, it is generally late onset disease as compared to someone with the ApoE e4 gene.
While ApoE e2/e2 alleles are associated with a higher risk of premature vascular disease, it is important to note that many factors in addition to lipid concentrations affect whether or not an individual develops vascular disease in general. These factors may include the presence of obesity, diabetes, and hypothyroidism.
ApoE e3/e3 is most often associated with healthy lipid metabolism. Testing that reveals the presence of this allele indicates there is likely no genetic risk associated with cardiovascular disease. ApoE e3 neither increases nor decreases risk for Alzheimer’s disease.
ApoE e4 (genotype e4/e4 or e4/e3) is present in about 25% of the general population and has been linked with a higher probability of atherosclerosis. Individuals with this genotype may have elevated levels of LDL-C, also known as “bad cholesterol”, as well as high triglycerides (especially when accompanied with a diet high in saturated fat). ApoE e4 increases the risk for early onset Alzheimer’s disease. A higher number of ApoE e4 alleles increases the risk of developing Alzheimer’s disease in general.
ApoE genetic testing is not intended to screen the general population for lipid abnormalities.
Whether you’re at risk for Alzheimer’s disease, cardiovascular disease, or neither condition, ApoE testing can provide you and your physician important information to better manage your health and wellness in the new year.
1“Alzheimer’s Disease Genetics Fact Sheet.” National Institute on Aging, U.S. Department of Health and Human Services, www.nia.nih.gov/health/alzheimers-disease-genetics-fact-sheet.
2Bird, Thomas D. “Early-Onset Familial Alzheimer Disease.” GeneReviews® [Internet]., U.S. National Library of Medicine, 18 Oct. 2012, www.ncbi.nlm.nih.gov/books/NBK1236/.
3Haan, Mary N., and Elizabeth R. Mayeda. Current Cardiovascular Risk Reports, Current Science Inc., Sept. 2010, www.ncbi.nlm.nih.gov/pmc/articles/PMC2908458/.
4“Heart Disease.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 28 Nov. 2017, www.cdc.gov/heartdisease/facts.htm.