Brain Injury and Alzheimer’s Disease
A moderate to severe Traumatic Brain Injury, or head trauma, is one of the strongest environmental risk factors for Alzheimer’s disease. Traumatic Brain Injury (TBI) refers to an injury in which normal brain function is disrupted by a bump, jolt, or blow to the head. These injuries are seen often with accidents such as motor vehicle accidents, bike accidents, and slip and falls. In fact, according to the Center for Disease Control and Prevention (CDC), nearly 36% of all traumatic brain injuries arise from falls and more than 17% are the result of a traffic accident (car, truck, motorcycle, pedestrian, or bicycle). According to the CDC, each year, an estimated 1.7 million Americans sustain a TBI. The CDC also explained that TBI’s are a contributing factor for nearly 31% of all injury-related deaths in the United States.
According to Kendall Walker, a post-doctoral associate in the Department of Neuroscience at Tufts University School of Medicine (TUSM), a serious TBI can lead to a dysfunction in the regulation of the enzyme BACE1. Elevations of this enzyme cause elevated levels of amyloid-beta. The key components of brain plaques associated with senility and Alzheimer’s disease. One of the most obvious changes in the brain after injury is the presence of inflammation, a complex reaction involving many different chemicals and cells in the brain. Even after a mild injury, large numbers of these cells, called microglia and astrocytes, are present in injured areas for several weeks. Researchers from the Perelman School of Medicine and the University of Pennsylvania are suggesting that Alzheimer’s disease-like neurodegeneration may be initiated or accelerated following a single TBI – even in young adults.
Moderate to severe TBI’s are caused most often by traumas, such as severe falls or motor vehicle accidents that result in the loss of consciousness. Concussions, the mildest form of TBI, account for about 75% of the 1.7 million TBI’s sustained each year. Studies have linked minor and severe brain trauma to brain disease, such as Alzheimer’s. In fact, the Journal of Neuroscience recently published a study that linked a single occurrence of TBI with significantly raising an individual’s chance of having Alzheimer’s. Alzheimer’s disease currently affects as many as 5.1 million Americans and is the most common cause of dementia for individuals age 65 and older.
The Journal of Neuroscience also investigated the presence of two key changes in the way the brain operates in both TBI victims and those who suffer from Alzheimer’s. The study suggests that the presence of these changes illustrated that brain injuries are one of the strongest environmental risk factors for the development of the degenerative disease. More than twenty years ago, scientists found a possible link between APOE4 (the genetic variation associated with an increased risk of Alzheimer’s) and higher rates of dementia after a head injury, as well as higher risk of increased accumulation of beta-amyloid plaques. APOE4 predisposes to inflammation, which causes neuronal injury and cognitive loss. Head injury associated with inflammation accelerates this process.
Although we do not know the causes of Alzheimer’s disease, we do know that changes in certain genes and environmental factors result in increased risk. Brain injury is probably the environmental factor most strongly linked to Alzheimer’s disease. Studies of large numbers of people who have had a TBI have shown that they are more likely to develop Alzheimer’s later in life. Also, some of the features of the disease have been found in the brains of people who have died after a brain injury. The reason for this link is not known.