Scientists do not yet fully understand what causes Alzheimer's but generally attribute the disease to genetic and environmental factors, with the possibility of lifestyle conditions also contributing to susceptibility. These causes seem to affect individuals inversely. The most important known risk factor of Alzheimer's disease is increasing age. Nutrition, exercise and long-term adverse health conditions such as high blood pressure and diabetes have also been linked to increased risk.
Alzheimer's is not necessarily hereditary. A rare form of the disease, early-onset familial Alzheimer's, is hereditary and predominantly occurs between the ages of 30 and 60. Most cases of Alzheimer's disease are late-onset (occurring after age 60) and do not present any striking or obvious familial patterns. However, genetic factors appear to increase a person's risk of developing late-onset Alzheimer's.
Although we still don’t know how Alzheimer’s disease begins, it seems likely that damage to the brain commences 10 years or more before symptoms arise and become apparent. During the earliest stage of Alzheimer’s, people are free of symptoms but harmful yet undetected changes are occurring in the brain, especially in the hippocampus, the part of the brain responsible for learning and memory. Abnormal protein deposits start to form amyloid plaques and neurofibrillary tangles throughout the brain. Healthy nerve cells begin to lose their ability to function and communicate with each other, and ultimately die. As nerve cells in the brain die, parts of the brain eventually shrink, bringing the disease to its final stages where the shrinkage spreads throughout entire brain regions, irreversibly damaging the remaining nerve cells.
Alzheimer's disease generally progresses through three stages: early (mild), middle (moderate) and late (severe).
Memory problems are typically one of the first signs of Alzheimer’s disease. Symptoms of early-stage Alzheimer’s disease include:
Other memory issues that arise beside memory loss may be the first signs of Alzheimer’s disease. These issues include difficulty communicating or finding the right words, visual and spatial issues and impaired reasoning or judgment assessments. This can cause irritability and frustration and greatly contribute to mood or personality changes.
As Alzheimer’s disease progresses to the middle stage, memory loss, cognition and confusion grow increasingly worse. People start to have problems recognizing family members and friends. Other symptoms of this stage include:
As Alzheimer’s disease becomes more severe and enters into the final stages, people lose the ability to communicate. They may sleep more, lose weight or have difficulty eating and swallowing. Often they become incontinent and eventually require living assistance.
The length of time from diagnosis of Alzheimer’s disease to death varies from person to person and depends on the stage of the disease and the age of the person. This period may span as little as three to four years if the person is over 80 years old when diagnosed, or as long as 10 years or more if the person is younger.
The only absolute way to detect Alzheimer's disease is to determine whether plaques and neurofibrillary tangles exist in brain tissue. Doctors can only make a diagnosis of "possible" or “probable” Alzheimer’s disease while a person is alive. Physicians with specialized training, including geriatricians, geriatric psychiatrists and neurologists, can diagnose Alzheimer's disease correctly up to 90 percent of the time.
To diagnose Alzheimer's disease, specialists must:
An early, precise diagnosis of Alzheimer's disease affords people and their families to plan accordingly for the future. It allows them time to process the diagnosis, discuss care options, find support and make legal and financial arrangements while the person with Alzheimer’s can still take part in the decision-making process.
Not all memory problems can be attributed to Alzheimer’s disease - mild forgetfulness is a normal part of the aging process. Memory loss and even dementia are often linked to treatable health issues, including side effects from medications, vitamin B12 deficiency and liver or kidney disorders. Emotional and environmental problems, such as stress, anxiety or depression, can also contribute to forgetfulness and may be mistaken or misdiagnosed for dementia.
Currently, no treatments are available that can prevent or cure Alzheimer's disease. However, four medications are available to treat Alzheimer’s symptoms by regulating chemicals in the brain to maintain cognition, memory and speaking skills for a limited time. These medications tend to work best for those in the early or middle stages of the disease.
For people with mild or moderate Alzheimer's, donepezil (Aricept), rivastigmine (Exelon) or galantamine (Razadyne®) may help. Donepezil is also approved to treat symptoms of moderate to severe Alzheimer's. Memantine (Namenda) is used to treat symptoms of moderate to severe Alzheimer's, although it also has limited effects. All of these medications may present side effects.
Other medications and approaches can also help control the behavioral symptoms of Alzheimer's disease, including sleeplessness, agitation, wandering, anxiety, anger and depression.
Scientists are currently studying many possible ways to prevent Alzheimer's disease, including lifestyle factors such as exercise and physical activity, healthy nutrition and mentally stimulating activities.
Research suggests that exercise may play a role in reducing the risk of Alzheimer’s disease. Animal studies show that, in older rats and mice, exercise increases both the number of small blood vessels that supply blood to the brain and the number of connections between nerve cells.
In addition, researchers have found that exercise raises the level of a nerve growth factor (a protein key to brain health) in an area of the brain that is important for memory and learning, and may stimulate the human brain’s ability to maintain old network connections and make new ones.
Conditions such as vascular disease, high blood pressure, heart disease and diabetes may increase the risk of Alzheimer’s disease. Many researchers are currently examining whether this risk can be reduced by preventing or controlling these conditions.
For example, lowering blood pressure to or below currently recommended levels may affect cognitive decline and the development of Mild Cognitive Impairment (MCI) and Alzheimer’s disease. A clinical trial is currently underway involving older adults with high systolic (upper number) blood pressure who have a history, or are at risk, of heart disease or stroke.
Diabetes is another disease that has been linked to Alzheimer’s. Past research suggests that abnormal insulin production contributes to Alzheimer’s-related brain changes (insulin is the hormone involved in diabetes). Diabetes treatments have been tested in patients with Alzheimer’s, but the results have not been conclusive.
Basic research helps scientists gain new knowledge about a disease process, including how and why it starts and progresses. Basic Alzheimer’s disease researchers primarily seek to identify the cellular, molecular and genetic processes that lead to the disease. Basic Alzheimer's research involves the study of:
Translational research grows out of basic research, creating new medications, devices and behavioral interventions aimed at preventing, diagnosing or treating a disease. An important goal of Alzheimer’s translational research is to increase the number and variety of potential new medications and other interventions that are approved for testing in humans. Scientists also examine medications approved to treat other diseases to determine if they might be effective for patients with Alzheimer’s.
The most promising interventions are analyzed in test-tube and animal studies to make sure they are safe and effective. Currently, a number of different substances are under development that may one day be used to treat the symptoms of Alzheimer’s disease and MCI.
Clinical research is medical research that involves people, including clinical studies (observation and information gathering involving large groups of people), as well as clinical trials (utilization of human participants to test medications, therapies, medical devices or behaviors in order to determine their safety and effectiveness).
Clinical trials are the best way to determine whether a particular intervention actually slows, delays or prevents Alzheimer’s disease. Clinical trial investigators may compare a potential new treatment to a standard treatment or placebo (mock treatment) or determine whether a certain behavior or condition affects the progress of Alzheimer’s or the chances of developing it.