What Causes Alzheimer's Disease?
In 1906, German psychiatrist and neuropathologist Dr. Alois Alzheimer examined the brain of a woman who had died after exhibiting memory loss, language problems and unpredictable behavior. He noticed changes in the tissue, including abnormal clumps and tangled bundles of fibers. These anomalies that cause the brain to shrink would become identifiers of what is now known as Alzheimer’s disease.
For more than a century, scientists have been trying to unravel the mysteries of this disease, which the Alzheimer’s Association says afflicts 6.2 million people in the United States. While there is no cure and still much to learn about its cause, Alzheimer’s disease research is in high gear, with about 200 active clinical trials and studies that are testing ways to understand, diagnose, treat and prevent the disease. Ochsner’s neuropsychology section is actively involved in research. There is over $4 million in funded research ongoing in the health system’s Cognitive Disorders and Brain Health Program.
That said, we do know a lot more about this form of dementia than we did in Dr. Alzheimer’s day.
Defining Alzheimer’s disease and dementia
Dementia is the general term for a group of brain disorders. Like the term heart disease, it covers a wide range of specific medical conditions. People with dementia experience abnormal brain changes that trigger a decline in thinking skills severe enough to impair daily life and independent function.
Symptoms of dementia vary from person to person and may include memory problems, mood changes, or difficulty walking, speaking or finding your way. It is a syndrome rather than a disease. A syndrome is a group of symptoms that doesn’t have a definitive diagnosis.
There are many causes for dementia; Alzheimer’s disease is the most common. The World Health Organization estimates that 47.5 million people around the world are living with dementia. Alzheimer’s disease accounts for 60% to 80% of the cases.
A change in memory is often the first sign of the disease, and some people may also have changes in mood, language or thinking skills. For example, early signs can appear as trouble remembering recent conversations, forgetting to pay the bills, or getting lost in familiar places. Others may first notice trouble with finding the right words to use in conversation or learning new skills at work.
Cognitive changes do not happen overnight. Instead, difficulties start off slowly at the beginning and become more noticeable over time. Most people with Alzheimer’s disease start having symptoms after age 65, although some have shown signs as early as age 40.
Alzheimer’s disease is a progressive disease, which means that it is irreversible and destroys brain cells over time. At the beginning, the disease targets parts of the brain responsible for memory and thinking skills, which is why these symptoms are usually the first to show. Eventually, the disease impairs the ability to carry out daily activities. Some people who suffer from it can live many years after being diagnosed. How quickly the disease progresses can vary from person to person. Research suggests that most patients live from four to eight years after being diagnosed, but some can live up to 20 years with the disease.
The search for a cause
Science has yet to nail down the exact cause of this disease, whose prevalence continues to grow in part because of the aging world population. We know that people with Alzheimer’s disease have brain cells burdened with a significant buildup of proteins called amyloid and tau. However, researchers have not yet determined what causes the buildups to occur. The disease can take root and go on for many years without symptoms. But as more proteins accumulate in brain cells, these cells malfunction and eventually die, causing the affected parts of the brain to shrink and symptoms to worsen.
Age is the top known risk factor for developing Alzheimer’s disease and other dementias. However, while growing older greatly increases risk, it is not a direct cause and these disorders are not a normal part of the aging process.
Family history is another significant risk factor. Those who have a parent or sibling with Alzheimer’s disease are more likely to develop the disease. The risk is even higher if more than one family member has the illness. In cases where Alzheimer’s disease and dementia runs in families, either heredity (genetics), environmental factors, or both, may play a role, according to the Alzheimer’s Association.
It is not uncommon for poor cardiovascular health to overlap with Alzheimer’s disease. Uncontrolled medical conditions like high blood pressure, high cholesterol and type 2 diabetes can worsen the symptoms of Alzheimer’s disease and increase the risk of developing dementia.
Some researchers estimate that older African American people are about twice as likely as older white people to have a diagnosis of Alzheimer’s disease, while older Latino people are about 1 1/2 times as likely compared to older white people. While the reasons for these differences are unclear, they are believed to involve many complex social, environmental and biological factors that interact with each other. Higher rates of vascular disease in these groups might play an important role. More research is needed to better understand how Alzheimer’s disease affects minority groups.
There is no cure for Alzheimer’s disease. Until recently, doctors focused primarily on addressing the symptoms to help people living with the disease and their caregivers to cope. Medications called cholinesterase inhibitors help a person with Alzheimer’s disease manage their memory problems. These medications may slow down the worsening of memory problems, but they do not reverse them.
In June 2021, the U.S. Food and Drug Administration approved Aduhelm (aducanumab) as a treatment option. The Alzheimer’s Association reports that Aduhelm is the first FDA-approved therapy to specifically target the underlying biology of Alzheimer’s disease. It is also the first new drug to gain federal approval for Alzheimer’s patients in almost 20 years.
However, the approval is not without controversy. While the FDA has declared the new drug as likely to help patients, numerous experts have argued that there is not enough evidence to establish the benefits and overcome health risks. In fact, the FDA’s decision to approve the drug leg some experts on the advisory committee to resign in protest.
One promising line of research suggests that strategies for overall healthy aging may help keep the brain healthy and potentially reduce the risk of developing Alzheimer’s disease and other dementias. These measures include treating vascular risk factors, eating a healthy diet, staying socially active, avoiding tobacco and excess alcohol, and exercising both the body and mind. These lifestyle habits are changes that anyone can make do to reduce their risk, and it is never too early to start.
Learn more about neuropsychologist Stella Tran, PhD.