Genes are passed down from a person's biological parents. They carry information that defines traits such as eye color and height. Genes also play a role in keeping the body's cells healthy.
Genetic mutations permanent change in one or more specific genes can cause diseases. If a person inherits a genetic mutation that causes a certain disease, then he or she will usually get the disease. Sickle cell anemia, cystic fibrosis, and some cases of early-onset Alzheimer's disease are examples of inherited genetic disorders. Other changes or differences in genes, called genetic variants, may increase or decrease a person's risk of developing a particular disease. When a genetic variant increases disease risk but does not directly cause a disease, it is called a genetic risk factor.
Identifying genetic variants may help researchers find the most effective ways to treat or prevent diseases such as Alzheimer's in an individual. This approach, called precision medicine , takes into account individual variability in genes, environment, and lifestyle for each person. The field of epigenetics is studying how such factors can alter a cell's DNA in ways that affect gene activity.
Sherva R, et al. Genetics of Alzheimer disease. Accessed Nov. The genetics of Alzheimer's disease. Alzheimer's disease genetics fact sheet. National Institute on Aging. Carch CM, et al. Alzheimer's disease risk genes and mechanisms of disease pathogenesis. Biological Psychiatry. Risk factors. Alzheimer's Association. Alzheimer's Disease Genetics Study.
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Add or change institution. Free access to newly published articles. Purchase access. Other common symptoms include agitation, restlessness, withdrawal, and loss of language skills. People with this disease usually require total care during the advanced stages of the disease.
Affected individuals usually survive 8 to 10 years after the appearance of symptoms, but the course of the disease can range from 1 to 25 years. Survival is usually shorter in individuals diagnosed after age 80 than in those diagnosed at a younger age. Death usually results from pneumonia, malnutrition, or general body wasting inanition.
Alzheimer disease can be classified as early-onset or late-onset. The signs and symptoms of the early-onset form appear between a person's thirties and mid-sixties, while the late-onset form appears during or after a person's mid-sixties. The early-onset form is much less common than the late-onset form, accounting for less than 10 percent of all cases of Alzheimer disease.
Alzheimer disease currently affects more than 5 million Americans. Because the risk of developing Alzheimer disease increases with age and more people are living longer, the number of people with this disease is expected to increase significantly in coming decades.
Some cases of early-onset Alzheimer disease are caused by gene mutations that can be passed from parent to child. This results in what is known as early-onset familial Alzheimer disease FAD.
When any of these genes is altered, large amounts of a toxic protein fragment called amyloid beta peptide are produced in the brain. This peptide can build up in the brain to form clumps called amyloid plaques , which are characteristic of Alzheimer disease.
A buildup of toxic amyloid beta peptide and amyloid plaques may lead to the death of nerve cells and the progressive signs and symptoms of this disorder.
Other cases of early-onset Alzheimer disease may be associated with changes in different genes, some of which have not been identified. Some evidence indicates that people with Down syndrome have an increased risk of developing Alzheimer disease. Down syndrome, a condition characterized by intellectual disability and other health problems, occurs when a person is born with an extra copy of chromosome 21 in each cell.
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