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Is Alzheimer's Disease Hereditary? Causes and Risks

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Is Alzheimer's Disease Hereditary?  Causes and Risks

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Alzheimer's disease is a chronic and progressive condition that affects a person's memory, thinking, and ultimately their movement.  It is the most common cause of dementia. Dementia can seriously impact an individual's ability to think, to make judgments, and to carry out everyday tasks.

Doctors have been aware of Alzheimer's for many years, but much remains unknown about it.

It is unclear why one person develops Alzheimer's, yet another person with a similar lifestyle, age, and background does not. Currently, there is no cure for Alzheimer's.

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.


Risk factors for Alzheimer's disease

Age is a major risk factor for Alzheimer's, but not the only one.

Researchers have identified several risk factors for Alzheimer's disease.

These include:

  • Age: According to the Alzheimer's Association, the single greatest risk factor for Alzheimer's disease is age. People over 65 years are more likely to develop Alzheimer's. By the time they are 85 years, 1 in 3 people are estimated to have the condition.
  • Family history: Having a close relative with Alzheimer's disease increases a person's chance of developing it.
  • Head trauma: A person who has had serious head trauma in the past, such as from a motor vehicle accident or from contact sports, appears to be at greater risk of developing Alzheimer's disease.
  • Heart health: Heart or vascular conditions may increase the chance of developing Alzheimer's disease. Examples include high blood pressure, stroke, diabetes, heart disease, and high cholesterol.

Heart or vascular conditions can damage blood vessels in the brain, and this may impact Alzheimer's disease. Latino and Black Americans may be at greater risk of developing vascular diseases such as diabetes, and therefore of Alzheimer's disease.

How can a genetic component affect Alzheimer's?

Scientists describe genetic risks for Alzheimer's in terms of two factors: risk and deterministic.

Risk genes

Risk genes increase the likelihood of a person having a certain disease. For example, a woman who has the BRCA1 and BRCA2 genes has a higher risk of developing breast cancer.

Researchers have identified several genes that present a risk for Alzheimer's. The most significant currently known is the apolipoprotein E-E4 gene. This is known as APOE-e4 gene.

According to the Alzheimer's Association, an estimated 20 to 25 percent of people with this gene may go on to have Alzheimer's disease.

While every person inherits an APOE gene of some form, the APOE-e3 and APOE-e2 genes are not associated with Alzheimer's disease. According to the Mayo Clinic, having the APOE-e2 gene appears to reduce the risk.

A person who receives the APOE-e4 gene from both parents is at greater risk of Alzheimer's disease. Having the gene may also mean that a person displays symptoms and can be diagnosed at an earlier age.

There are other genes that may be linked with late-onset Alzheimer's. Researchers have to find out more about how these genes increase Alzheimer's risk.

Several of these genes regulate factors in the brain, such as nerve cell communication and inflammation in the brain.

Deterministic genes

A person with deterministic genes will definitely develop the condition. There are three specific genes that have been identified as deterministic for Alzheimer's disease.

The buildup of amyloid plaques is a classic feature of Alzheimer's dementia.

These are:

  • Amyloid precursor protein (APP)
  • Presenilin-1 (PS-1)
  • Presenilin-2 (PS-2)

These genes are responsible for causing the brain to build up too much of a protein called amyloid-beta peptide. This toxic protein can create clumps in the brain that cause nerve cell damage and death associated with Alzheimer's disease.

However, not all people with early-onset Alzheimer's have irregularities of these genes. If a person does have these genes, the Alzheimer's they develop is known as familial Alzheimer's disorder. This type of Alzheimer's is rare.

According to the Alzheimer's Association, familial Alzheimer's represents less than 5 percent of all cases in the world.

Deterministic Alzheimer's disease typically occurs before the age of 60 years, and sometimes as early as age 30 to 40 years.

Effect of genes in other types of dementia

A number of types of dementia are related to other genetic malformations.

Huntington's disease affects chromosome 4, leading to progressive dementia. Huntington's disease is a dominant genetic condition. If a person's mother or father has the condition, they will pass on the gene and their offspring will develop the disease.

Unfortunately, symptoms do not usually appear until between the ages of 30 and 50 years. This can make it difficult to predict before having children.

Dementia with Lewy bodies or Parkinson's disease may have a genetic component. However, other factors, apart from genetics, also play a role.

Early signs and symptoms of Alzheimer's disease

Alzheimer's disease usually involves a gradual loss of memory and brain functioning.

Confusion and disorientation are common symptoms of Alzheimer's.

Early symptoms may be periods of forgetfulness or memory loss. Over time, a person may become confused or disoriented as to where they are in familiar settings, including in the home.

Other symptoms could include:

  • Changes in mood or personality
  • Confusion as to time or place
  • Difficulty with routine tasks, such as doing laundry, sweeping, or cooking
  • Difficulty recognizing common objects
  • Difficulty recognizing people
  • Frequently misplacing things

Aging can result in impaired memory, but Alzheimer's disease results in more consistent periods of forgetfulness.

Over time, a person with Alzheimer's may need more and more help with activities of daily living, such as brushing teeth, getting dressed, and cutting food. They may become easily agitated, restless, experience personality withdrawals, and have difficulty speaking.

According to the National Institutes of Health, the survival rate for a person with Alzheimer's disease is usually 8 to 10 years after symptoms first appear. Because a person cannot care for themselves or they may not recognize the importance of eating, common causes of death include malnutrition, body wasting, or pneumonia.

When to see a doctor

Discussing the need for medical attention regarding memory changes can be challenging, but it is important to seek help to rule out other conditions. Other conditions that can cause dementia include a urinary tract infection or a brain tumor.

Before an appointment, family members should consider making a list of medications the person is taking. The doctor can review it and ensure the medications are not causing symptoms.

Keeping a journal of noticeable symptoms as they develop over time can also help a doctor to establish potential patterns.

Although genetic testing is available to detect these genes for Alzheimer's disease, doctors do not generally recommend this testing for late-onset diseases. This is because the presence of the genes does not necessarily mean that a person will have the condition. In this case, testing could cause unnecessary worry, anxiety, and fear.

However, if a person has a family history of early-onset Alzheimer's, they may wish to pursue genetic testing. Before this takes place, most doctors will recommend meeting with a genetic counselor beforehand, to discuss the pros and cons of genetic testing, and how the results could be interpreted.

Sometimes, a doctor may recommend genetic testing when people show early Alzheimer's symptoms as this may dictate treatments and potential for therapeutic drug trials.

A number of large-scale studies are currently taking place into Alzheimer's disease and heredity.

Those 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 tracks information on people who have more than two relatives that were diagnosed with Alzheimer's after age 65 years.

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