Alzheimer’s disease (AD) refers to a slowly progressive loss of nerve cells (neurons) in the brain. Symptoms of the illness usually unfold slowly over a period of years. Neurons involved in memory and thinking are affected first, while movement and sensation are only affected in the very late stages.
Several different forms of AD have been discovered – a few rare forms are strongly inherited and become symptomatic in mid-life, while the vast majority result from complex interactions between genes and the environment, and do not become symptomatic until late-life.
AD is the sixth leading cause of death in the United States, and the only disease among the top 10 in America that cannot be prevented, cured, or slowed, according to the Alzheimer’s Association.
How does Alzheimer’s disease differ from dementia?
Alzheimer’s disease (AD) is a brain disease. It is the most common cause of dementia. Among people over the age of 65, AD accounts for over two-thirds of dementia cases. Dementia describes a clinical syndrome of progressive loss of thinking, memory, and other cognitive abilities impairing daily function. The most common symptom of dementia caused by AD is a gradual worsening of memory.
By definition, all forms of Alzheimer’s disease (AD) share two features in common, namely the abnormal accumulation of two misfolded proteins: 1) beta-amyloid (a-beta) and 2) phosphorylated tau (p-tau). The accumulation of these proteins may result from either over-production in or decreased clearance from the brain.
A-beta amyloid proteins accumulate at synapses (sites of inter-neuronal communications) to form amyloid plaques. This process jams the communication of information within complex networks of brain cells. Communication normally involves the release of chemical neurotransmitters from the endings of one nerve cells (pre-synaptic terminals), which then dock at receptors of receiving nerve cells (post-synaptic terminals).
P-tau form helical filaments which are known as “neurofibrillary tangles” within the neuron cell body and “neurites” at nerve cell terminals. This causes problems in the vital transportation of molecules within the nerve cell, which takes place through a system of microtubules akin to those that transport water and nutrients to the leaves of plants and trees.
Billions of neurons and trillions of synapses in the human brain are organized in complex networks specialized for sensory perception and movement, as well as memory and intellectual processing (higher cognitive functions). The networks for higher cognitive function suffer the brunt of damage in AD.
What are the early signs and symptoms of Alzheimer’s disease?
The ability to store new experiences and learn new information is affected first in Alzheimer’s disease (AD). The earliest signs may be difficult to distinguish from slowing associated with the normal aging process. Even in the best of circumstances, human memory is limited and imperfect. We only remember things that we notice and pay attention to, which is only a fraction of what is taking place around us. We choose to pay attention to things that are personally important to us.
Persons affected by AD, however, have difficulty remembering new information that is of personal importance and despite paying good attention. For example, it is normal to misplace ones keys, if one is not paying attention; but it would be worrisome if someone forgot to pay a large bill or missed an important family event.
Early on, AD also affects executive functions. This includes the ability to actively organize, analyze, and solve problems. Usually people with early Alzheimer’s disease are not fully aware of the decline in their memory skills and have difficulty judging the impact these changes may have on their safety or daily function.
What are the later signs and symptoms of Alzheimer’s disease?
As the illness progresses, decline becomes evident in visual-spatial and language abilities. The combined loss of memory and visual-spatial orientation places a person at greater risk of getting lost in unfamiliar surroundings. This can result in confusing experiences for a person with Alzheimer’s disease (AD) who is walking or driving alone. The person with AD may experience difficulty finding words, understanding complex instructions, or following multiple step commands. Thus, in the mid stages of AD, a person needs increased assistance with activities of daily living and personal care such as dressing, grooming, and bathing. If the illness goes on for many years, independence is lost for most of the functions of daily life. And in the most advanced stages, walking and swallowing are affected. At this point, the person can be at risk for infections such as pneumonia or sepsis.
Does Alzheimer’s disease affect mood and behavior?
Changes in mood and behavior, as well as memory loss and thinking, are frequently observed in those with Alzheimer’s disease, but differ greatly from one person to another. Depression, irritability, defensiveness, and social withdrawal are often noted in the early stages. Suspiciousness, paranoia, and visual hallucinations may develop in the later stages. Various degrees of hyperactivity, agitation, wandering, and sleep disturbances may also occur. These behavioral symptoms can sometimes be improved by thoughtful modifications of interpersonal interactions or changes in the environment. Medications may also be helpful.
About one person out of 20 over the age of 65 develops Alzheimer’s disease (AD) and less than one person in a thousand under the age of 65. However, it is important to note that although people do tend to become forgetful as times goes on, the vast majority of people over 80 stay mentally alert.
Through research, the multiple steps leading to the formation and clearance of the abnormal proteins that form plaques and tangles in the Alzheimer’s disease brain are becoming increasingly clear. This knowledge will lead to new ideas about ways to slow down or stop the disease process. The safety and effectiveness of new approaches to treatment are then put to test in carefully-controlled studies known as clinical trials.