Is Dementia Hereditary?

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When 70s teen heartthrob David Cassidy went public with his dementia diagnosis earlier this year, I was shocked. David was a friend of our family, and my uncle, Donny Osmond, was his contemporary. My dad, Wayne, and the other Osmond Brothers performed with David many times over the years, and they always spoke highly of him. This long-time entertainer, who made female fans swoon as part of The Partridge Family, has fallen victim to a pervasive disease that affects the lives of millions.

Even before his diagnosis, David was no stranger to dementia. In an interview with People Magazine, he recounted watching his grandfather struggle with dementia and saw his mother “disappear” from it as well. David’s announcement that he’s battling the disease may prompt many to ask themselves about their own risk of inheriting dementia.

How much do our genetics affect our chances of developing Alzheimer’s disease and other forms of dementia? More importantly, is there anything we can do to lower our chances of meeting the same fate as our loved ones? The future is uncertain, but researchers are getting closer to finding some answers.

What are the common forms of dementia?

Alzheimer’s accounts for about 60 to 80 percent of dementia cases and is the most common form of the disease. This is the form of dementia most people think about when faced with symptoms like memory problems, disorientation, behavior changes, difficulty communicating and walking and the eventual total loss of cognitive and motor skills. Alzheimer's is the sixth leading cause of death in the United States.

Despite its prevalence in the aging population, Alzheimer’s is not a natural part of aging. Instead, damage to the brain results from abnormal clumps of plaque and fiber bundles collecting throughout the hippocampus, and damaged nerve cells compromise the neuron’s ability to transmit messages to different parts of the brain. Research has found that in as many as 99 percent of cases, Alzheimer’s disease is not inherited. But for the 1 percent of inherited cases, the disease develops much easier, with onset as early as age 30. Three genes -- APP, PS1 and PS2 -- have been identified as causing this very rare form of Alzheimer’s.

The second most common form of dementia, vascular dementia, is typically not hereditary but is caused by poor blood flow to the brain, which deprives brain cells of the nutrients and oxygen they need to function normally. Like Alzheimer’s and other forms of dementia, symptoms of vascular dementia include impaired judgment and impaired motor and cognitive skills.

“One of the ten different dementia types, vascular dementia can result from any number of conditions which narrow the blood vessels, including stroke, diabetes, and hypertension,” says Dr. Harvey Gilbert, M.D. This includes stroke-related dementia and subcortical dementia. Healthy lifestyle habits can help reduce the risk of developing most of these conditions and vascular dementia is inherited only in very rare cases.

What factors influence our risk of getting Alzheimer’s?

In David Cassidy’s case, his condition can be traced back to his mother, Evelyn Ward, who died of dementia at the age of 89 in 2012. Researchers are still unable to pinpoint the exact cause of Alzheimer’s and other forms of dementia. However, experts have identified three main areas that influence our risk factors.

1. Age

Experts are unable to determine why the odds of getting Alzheimer’s increases with age. Still, the Alzheimer’s Association says the likelihood of developing this form of dementia doubles every five years after the age of 65. And the risk increases to 50 percent after the age of 85.

2. Family History

Most clinicians like to look at the full range of first, second, and third-degree relatives to create an adequate health profile for patients. “When we talk about these diseases where family history provides information, we use it to hypothesize the risk factors,” said Lisa Cannon-Albright, Ph.D., chief of the Division of Genetic Epidemiology and the Division of Cardiovascular Genetics at University of Utah's School of Medicine. “Learning the family history just illustrates your average risk.”

This information doesn’t guarantee that you’ll one day have this disease, though.

3. Genetics

Innovations in genetic technologies have now identified two types of genes that can determine the onset of dementia, risk genes and deterministic genes.

Risk genes If present, risk genes will increase the likelihood of developing dementia, but having them doesn’t guarantee it will happen. This gene with the big name, apolipoprotein E-e4, among others, may be a factor in 20 to 25 percent of Alzheimer’s cases, according to the Alzheimer’s Association.

Deterministic genes Unlike risk genes, the presence of deterministic genes is directly linked to the onset of dementia. Scientists have identified three proteins: amyloid precursor protein (APP), presenilin-1 (PS-1), and presenilin-2 (PS-2) that, when combined, are known as familial Alzheimer’s disease. Symptoms for people with these genes always develop before the age of 60. Yet, true familial Alzheimer’s is surprisingly rare, only accounting for less than one percent of all cases.

Does the environment increase our risk of getting Alzheimer’s?

We may not be able to outsmart genetics when it comes to disease. But in many cases, we not only share genes with our relatives, we also share their lifestyles. According to the Centers for Disease Control and Prevention,“People with a family history of disease may have the most to gain from lifestyle changes and screening tests. In many cases, adopting a healthier lifestyle can reduce your risk for diseases that run in your family.”

Studies support the connection between good heart health and brain health with growing evidence that the risk of developing dementia increases with many of the conditions that damage the heart and blood vessels. These include high blood pressure, heart disease, stroke, diabetes, and high cholesterol. Even if your family history doesn’t show signs of disease, adopting healthy habits can delay (or prevent) the onset of diseases, including Alzheimer’s and other forms of dementia.

So, are we doomed to inherit the same fate as our relatives? Cannon-Albright is convinced the answer is no. “The important thing to remember is that your health isn’t destined to always meet the same fate as those of your relatives,” she said. Further, learning through family history and genetic technologies will help researchers track patterns that could ultimately make dementia and other diseases a thing of the past.

Dr. Amy Osmond Cook

Amy Osmond Cook is executive director of the Association of Skilled Nursing Providers, and is a regular health and wellness contributor to the Orange County Register, Daily Herald, Senior Scene, Senior Housing Forum and more. See full bio