Alzheimer’s disease is a chronic, progressive condition that impairs memory, thinking, and movement. Some research suggests that a person is at increased risk for developing Alzheimer’s Disease if a relative has the disorder.
Doctors have been aware of Alzheimer’s for many years, but many aspects of the condition and a possible cure remain unknown.
The causes of Alzheimer’s are unclear.
Current research suggests that multiple factors may contribute to the development of Alzheimer’s. One of these is genetics or heredity.
Genetic factors may also impact how a doctor prescribes medications to treat Alzheimer’s disease.
Scientists describe genetic risks for Alzheimer’s in terms of two factors: Risk genes and deterministic genes.
When a person has risk genes, it means they have an increased chance of developing a disease. For example, a woman with the BRCA1 and BRCA2 genes has a higher risk of developing breast cancer.
Deterministic genes may directly cause a disease to develop.
Scientists have found several risk and deterministic genes for Alzheimer’s.
Several genes present a risk for Alzheimer’s. The gene with the most significant connection to Alzheimer’s risk is the apolipoprotein E-E4 gene (APOE-e4).
According to the Alzheimer’s Association, an estimated 20–25 percent of people with this gene may go on to have Alzheimer’s disease.
A person who inherits the APOE-e4 gene from both parents has a higher risk of developing Alzheimer’s disease than a person who inherits the gene from only one.
Having the gene may also mean that a person displays symptoms at an earlier age and receive an earlier diagnosis.
Other genes may have effects on late-onset Alzheimer’s and its development. Scientists need to do more research to learn how these genes increase Alzheimer’s risk.
Several of these genes regulate certain factors in the brain, such as inflammation and the way that nerve cells communicate.
While every person inherits an APOE gene of some form, the APOE-e3 and APOE-e2 genes have no association with Alzheimer’s disease. APOE-e2 might even provide protective effects on the brain against the disease.
Researchers have identified three specific deterministic genes that may cause Alzheimer’s disease:
- amyloid precursor protein (APP)
- presenilin-1 (PS-1)
- presenilin-2 (PS-2)
These genes are responsible for an excessive buildup of amyloid-beta peptide. This is a toxic protein that clumps together in the brain. This buildup causes the nerve cell damage and death that is characteristic of Alzheimer’s disease.
However, not all people with early-onset Alzheimer’s have these genes. A person with these genes who develops Alzheimer’s has a rare type known as familial Alzheimer’s disorder.
According to the Alzheimer’s Association, familial Alzheimer’s represents less than 5 percent of all cases in the world.
According to the Association, Alzheimer’s caused by deterministic genes typically occurs before the age of 65 years. It can sometimes develop in people who are in their 40s and 50s.
Effect of genes in other types of dementia
Some types of dementia have links to other genetic malformations.
Huntington’s disease, for example, alters chromosome 4, which can lead to progressive dementia. Huntington’s disease is a dominant genetic condition. This means that if either parent has the condition, they can pass on the gene to their offspring and they will develop the disease.
Symptoms of Huntington’s disease do not usually become evident until a person reaches 30–50 years of age. This can make it difficult for doctors to predict or diagnose before a person has children and passes on the gene.
Researchers think that dementia with Lewy bodies or Parkinson’s dementia may also have a genetic component. However, they also believe that other factors outside of genetics might play a role in the development of these conditions.
Researchers have identified several risk factors for Alzheimer’s disease.
- Age: The most significant risk factor for Alzheimer’s disease is age. People over 65 years of age are more likely to develop Alzheimer’s than younger people. By 85 years of age, the Alzheimer’s Association estimate that 1 in 3 people have the condition.
- Family history: Having a close relative with Alzheimer’s disease increases the risk of developing it.
- Head trauma: People with previous instances of severe head trauma, such as from a motor vehicle accident or contact sports, appear to be at higher risk of developing Alzheimer’s disease.
- Heart health: Health problems in the heart or blood vessels may increase the chance of developing Alzheimer’s disease. Examples include high blood pressure, stroke, diabetes, heart disease, and high cholesterol. These can damage blood vessels in the brain, impacting Alzheimer’s disease risk.
Alzheimer’s disease usually involves a gradual loss of memory and brain function.
Early symptoms may include periods of forgetfulness or memory loss. Over time, a person may experience confusion or disorientation in familiar settings, including in the home.
Other symptoms could include:
- changes in mood or personality
- confusion about time or place
- difficulty with routine tasks, such as doing laundry or cooking
- difficulty recognizing common objects
- difficulty recognizing people
- frequently misplacing objects and belongings
The aging process might naturally impair a person’s memory, but Alzheimer’s disease leads to more consistent periods of forgetfulness.
Over time, a person with Alzheimer’s may need an increasing amount of assistance with daily living, such as brushing teeth, getting dressed, and cutting food.
They may also experience agitation, restlessness, personality withdrawals, and speech problems.
According to the National Institutes of Health, the survival rate for a person with Alzheimer’s disease is usually 8 to 10 years after the first appearance of symptoms.
Seeking medical assistance for a person who demonstrates these symptoms is vital, even though the discussion might be a difficult one. A doctor can rule out other diseases that might cause dementia, such as a urinary tract infection or brain tumor.
Before an appointment, family members should make a list of any medications the person with symptoms is currently taking. The doctor can review the list and make sure dementia symptoms are not side effects of current medications.
Keep a journal of noticeable symptoms as they develop over time to help a doctor establish potential patterns.
Although genetic testing that can detect the genes that have links to Alzheimer’s disease is available, doctors do not generally recommend this testing for late-onset diseases.
The presence of the genes does not necessarily mean that a person will have the condition. Testing could cause unnecessary worry, anxiety, and fear.
However, a person with a family history of early-onset Alzheimer’s may wish to pursue genetic testing. Most doctors will recommend meeting with a genetic counselor beforehand to discuss the pros and cons of genetic testing, and how they can interpret the results.
Sometimes, a doctor may recommend genetic testing when people show early Alzheimer’s symptoms, as this may dictate possible treatments and potential for therapeutic drug trials.
Alzheimer’s disease has links to a number of genes. Some, such as the APOE-e4 gene, increase the risk of developing the disease but do not always lead to an Alzheimer’s diagnosis.
Others, such as the APP gene, directly cause the disease to develop. However, this is a rare type known as familial Alzheimer’s that occurs in less than 5 percent of people with the disease.
Researchers are currently undertaking some large-scale studies on Alzheimer’s disease and its links to heredity.
People who would like to contribute to the body of knowledge could contact researchers from the National Institute on Aging, who sponsor the Alzheimer’s disease genetics study.
The study, which will run until the year 2021, tracks information on people with more than two relatives who received an Alzheimer’s diagnosis after the age of 65 years old.