What does the APOE4 gene determine and what else has it been linked to?
Many people wonder if Alzheimer'southward affliction runs in the family. A person'due south chance of having the affliction may be higher if he or she has certain genes passed down from a parent. However, having a parent with Alzheimer's does not e'er mean that someone will develop it.
What Are Genes?
Each human jail cell contains the instructions a cell needs to do its job. These instructions are made up of Deoxyribonucleic acid (deoxyribonucleic acid), which is packed tightly into structures called chromosomes. Each chromosome has thousands of segments called genes.
Genes are passed downward from a person's biological parents. They carry data that defines traits such as centre color and acme. Genes also play a role in keeping the body'due south cells good for you.
Bug with genes—even small changes to a factor—can crusade diseases similar Alzheimer's.
Practice Genes Cause Diseases?
Genetic mutations (permanent change in one or more specific genes) can cause diseases. If a person inherits a genetic mutation that causes a sure disease, then he or she volition usually get
the disease. Sickle cell anemia, cystic fibrosis, and some cases of early-onset Alzheimer's illness are examples of inherited genetic disorders.
Other changes or differences in genes, called genetic variants, may increase or decrease a person'due south risk of developing a particular affliction. When a genetic variant increases disease take chances but does not directly cause a disease, information technology is called a genetic risk factor.
Identifying genetic variants may help researchers detect the almost effective ways to treat or prevent diseases such as Alzheimer'south in an private. This approach, called precision medicine, takes into account individual variability in genes, environment, and lifestyle for each person.
The expression of genes—when they are "switched" on or off—can be affected, positively and negatively, by ecology and lifestyle factors, such as practice, diet, chemicals, or smoking. The field of epigenetics is studying how such factors can modify a cell'southward DNA in means that affect gene activity.
Genes and Alzheimer's Disease
There are two types of Alzheimer's—early-onset and tardily-onset. Both types have a genetic component.
Late-Onset Alzheimer's Illness
Most people with Alzheimer's take the late-onset form of the disease, in which symptoms become apparent in their mid-60s and afterward.
Researchers have not found a specific gene that directly causes tardily-onset Alzheimer'due south disease. Yet, having a genetic variant of the apolipoprotein E (APOE) gene on chromosome 19 does increase a person'south risk. The APOE gene is involved in making a protein that helps behave cholesterol and other types of fat in the bloodstream.
APOE comes in several different forms, or alleles. Each person inherits 2 APOE alleles, one from each biological parent.
- APOE ε2 is relatively rare and may provide some protection against the disease. If Alzheimer's disease occurs in a person with this allele, information technology usually develops afterward in life than it would in someone with the APOE ε4 gene.
- APOE ε3, the nigh common allele, is believed to play a neutral role in the illness—neither decreasing nor increasing risk.
- APOE ε4 increases hazard for Alzheimer's disease and is also associated with an earlier historic period of disease onset. Having one or 2 APOE ε4 alleles increases the risk of developing Alzheimer's. About 25 pct of people comport one copy of APOE ɛ4, and 2 to 3 percent conduct 2 copies.
APOE ε4 is called a risk-factor gene because it increases a person's run a risk of developing the illness. However, inheriting an APOE ε4 allele does not mean that a person will definitely develop Alzheimer's. Some people with an APOE ε4 allele never get the disease, and others who develop Alzheimer'south exercise not have whatsoever APOE ε4 alleles.
Recent enquiry indicates that rare forms of the APOE allele may provide protection against Alzheimer's disease. More than studies are needed to decide how these variations might delay disease onset or lower a person's adventure.
Early-Onset Alzheimer's Disease
Early on-onset Alzheimer'southward disease is rare, representing less than x percent of all people with Alzheimer'due south. Information technology typically occurs between a person's 30s and mid-60s. Some cases are caused past an inherited modify in one of iii genes.
The iii single-factor mutations associated with early-onset Alzheimer's disease are:
- Amyloid precursor protein (APP) on chromosome 21
- Presenilin 1 (PSEN1) on chromosome 14
- Presenilin two (PSEN2) on chromosome one
Mutations in these genes result in the production of aberrant proteins that are associated with the disease. Each of these mutations plays a part in the breakdown of APP, a protein whose precise role is not nevertheless fully understood. This breakdown is part of a process that generates harmful forms of amyloid plaques, a hallmark of Alzheimer'southward illness.
A child whose biological mother or male parent carries a genetic mutation for ane of these 3 genes has a l/50 hazard of inheriting that mutation. If the mutation is in fact inherited, the child has a very strong probability of developing early-onset Alzheimer's illness.
For other cases of early-onset Alzheimer's, research has shown that other genetic components are involved. Studies are ongoing to place additional genetic risk variants.
Having Down syndrome increases the risk of developing early-onset Alzheimer's illness. Many people with Down syndrome develop Alzheimer's as they get older, with symptoms appearing in their 50s or 60s. Researchers believe this is because people with Down's syndrome are born with an extra copy of chromosome 21, which carries the APP gene.
For more information, run across NIA's Early-Onset Alzheimer's Disease: A Resource List.
Genetic Testing for Alzheimer'southward Disease
A claret test can place which APOE alleles a person has, but results cannot predict who will or will not develop Alzheimer'due south affliction. Currently, APOE testing is used primarily in research settings to identify study participants who may have an increased risk of developing Alzheimer'due south. This knowledge helps scientists look for early encephalon changes in participants and compare the effectiveness of possible treatments for people with different APOE profiles.
Genetic testing is also used by physicians to help diagnose early-onset Alzheimer'southward disease and to test people with a strong family history of Alzheimer's or a related brain illness.
Genetic testing for APOE or other genetic variants cannot determine an individual's likelihood of developing Alzheimer'southward illness—just which risk factor genes a person has. It is unlikely that genetic testing will ever exist able to predict the disease with 100 percent accuracy, researchers believe, because too many other factors may influence its development and progression.
Some people learn their APOE status through consumer genetic testing or think about getting this kind of exam. They may wish to consult a doctor or genetic counselor to meliorate understand this type of test and their exam results. General data about genetic testing can be found at:
- Genetic Testing
- What is Direct-to-Consumer Genetic Testing?
- Getting a Genetic Examination
- Genetic Testing FAQ
Alzheimer'due south Genetics Research
Discovering all that we tin about the part of Alzheimer'due south disease genetic take chances and protective factors is an important area of research. NIA supports several major genetics enquiry programs. Agreement more than about the genetic basis of the affliction will assistance researchers to:
- Reply a number of basic questions—What makes the affliction process begin? Why do some people with retention and other thinking problems develop Alzheimer's while others practise non?
- Determine how genetic run a risk and protective factors may interact with other genes and lifestyle or environmental factors to affect Alzheimer's risk in any one person.
- Place people who are at high take a chance for developing Alzheimer's then they can benefit from new interventions and treatments every bit soon as possible.
- Explain differences in Alzheimer's disease gamble and protection amidst racial groups and sexes.
- Focus on new prevention and treatment approaches
For More Data About Alzheimer's Affliction Genetics
NIA Alzheimer'south and related Dementias Teaching and Referral (ADEAR) Centre
800-438-4380
adear@nia.nih.gov
world wide web.nia.nih.gov/alzheimers
The NIA ADEAR Center offers information and free print publications almost Alzheimer's and related dementias for families, caregivers, and health professionals. ADEAR Center staff answer telephone, email, and written requests and make referrals to local and national resource.
National Center for Biotechnology Data
National Library of Medicine
www.ncbi.nlm.nih.gov
This content is provided by the NIH National Institute on Crumbling (NIA). NIA scientists and other experts review this content to ensure information technology is authentic and up to date.
Content reviewed: December 24, 2019
Source: https://www.nia.nih.gov/health/alzheimers-disease-genetics-fact-sheet#:~:text=APOE%20%CE%B54%20increases%20risk%20for,the%20risk%20of%20developing%20Alzheimer's.
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