Alzheimer’s disease is the most common cause of dementia, accounting for 60-80% of all dementia cases. The majority of Alzheimer’s cases arise in adults aged 65 and older, but Alzheimer’s disease is not a normal part of aging.
Unfortunately, the causes of Alzheimer’s disease are unknown. However, scientists have identified certain risk factors that appear to increase the likelihood of developing Alzheimer’s. Risk factors include age, a family history of Alzheimer’s, genetics, traumatic brain injury and overall cardiovascular health. While certain things — age, family history, genetics — are unpreventable, other risk factors — brain injury and overall health while you age — can be influenced by lifestyle and daily practices.
Alzheimer’s disease, like other forms of dementia, manifests in the brain. Specifically, Alzheimer’s causes nerve cell death and loss of brain tissue, meaning that over time, the brain shrinks and loses many of its functions.
Scientists have identified two things that appear to be responsible for the negative effects of Alzheimer’s disease on the brain: amyloid plaques and tau tangles. Although plaques and tangles exist in healthy individuals, their presence is much greater in the brains of Alzheimer’s patients.
Amyloid plaques form when pieces of a large protein, amyloid precursor protein, clump together. These pieces, called beta-amyloid proteins, clump together as plaques between neurons. One mutated amyloid can cause nearby amyloid groups to mutate, leading to the formation of large plaques. Amyloid plaques damage cells in the brain, leading to neuron death. Unfortunately, the body cannot take care of these plaques, leading to mass aggregation of amyloid plaques in the brain.
Tau tangles form when proteins called tau, stick to each other and become tangled. Tau is a naturally occurring protein that helps stabilize neurons in the brain. However, in Alzheimer’s disease, a mutated form of tau causes tau proteins to stick together rather than supporting neurons. Visually, this resembles tangles. Tau tangles impede neurons from communicating with each other, and even lead to neuron degeneration.
Scientists have identified these two mutated proteins as the leading cause of brain degeneration in Alzheimer’s patients. However, this list is non-conclusive — the causes and effects of Alzheimer’s disease are still actively being researched.
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“What Happens to the Brain in Alzheimer’s Disease?” National Institute on Aging. U.S. Department of Health and Human Services, n.d.