Alzheimer’s disease has become the focus of more and more attention in recent years; after all, it touches almost every family either directly or indirectly. Generally, people over 65 years of age have a higher chance of getting Alzheimer’s although people of 30 years of age or younger can still get it, depending on family history. In the population at large one in 20 people between 70 and 74 are affected, and almost 1 in 3 people over 90 are affected since the risk of developing the disease increases with age. The disease is the 6th leading cause of death in the United States (though may even be as deadly as heart disease or cancer) and in 2012 alone, $200 billion was spent on payments (private and public healthcare) for Alzheimer’s.
Alzheimer’s is inherited in an autosomal dominant pattern; one copy of the altered gene in each cell causes Alzheimer’s. More specifically one copy of APOE e4 allele, a section of the genetic code usually obtained from an affected parent, causes an increased chance of getting Alzheimer’s; two copies create a greater risk. This does not mean that the APOE e4 allele gives Alzheimer’s; you can get Alzheimer’s without the APOE e4 allele and if you have the APOE e4 allele, it doesn’t mean you will get Alzheimer’s.
Early onset Alzheimer’s is caused by mutations in one of three genes: APP, PSEN1, or PSEN2. Large amounts of a toxic protein fragment called amyloid beta peptide are produced around the neurons in the brain when any one of those genes is altered; inside the neurons toxic protein tau accumulates. Peptide builds up and forms amyloid plaques. Buildup of amyloid beta peptide leads to the death of nerve cells and can cause Alzheimer’s disease. In those people, the disease develops before the age of 65, usually at around 30.
A fully-grown brain has 100 billion neurons, each of these neurons has extensions like branches on a tree. These branches allow each individual neuron to form specific connections, or synapses, with other neurons. From these synapses, information travels through the use of chemical pulses given off by one neuron and recognized by the next neuron, which in turn releases another chemical signal in an unending chain. Through the use of synapses the brain can send messages quickly and constantly, creating the basis of memories, thoughts, sensations, emotions, movements and skills. In Alzheimer’s disease, the sending of information between synapses begins to fail, the number of synapses in the brain declines and some neurons even die. The accumulation of beta-amyloid outside neurons interferes with the neuron-to-neuron communication of synapses and it leads to cell death. Inside the neuron, abnormally high levels of tau block the passage of nutrients and other essential molecules throughout the cell, leading to its decline and eventual death. The brain of someone affected with Alzheimer’s disease shows a large reduction in the number of synapses due to cell loss and the dead debris of neurons.Credit: intechopen.com
To better understand the disease, it is first important to establish the definition of dementia: a disease or condition that develops when nerve cells in the brain die or cease to work due to a build up of plaque and proteins. This debilitating process causes changes in memory, behavior and rational thought. Alzheimer’s disease is always fatal, but is rarely listed as cause of death. Instead, the immediate cause of death, such as pneumonia, is listed on death certificates, a state of affairs that ignores the fact that dementia is an important underlying factor.
Secondly, we must learn to recognize Alzheimer’s. The phenotype (physical characteristics) of this disorder include: muscle loss due to inactivity, compulsive and repetitive behavior, weight loss even if sufficient food is eaten, reduction in efficiency of immune system, repetitive speech, restlessness, aggression, and vacant aspect. The symptoms, on the other hand, include loss of memory (more than age related); failure to recognize family, friends, objects; difficulty planning and solving problems; difficulty identifying month or day of the week; difficulty doing simple tasks which occur during daily life; puzzlement with time and place; difficulty understanding images and relationships; difficulty following instructions; problems arise with words in speech or written language; inability to retrace steps and inability to remember where things have been put; wandering, disrupted sleep cycle; poor judgment; difficulty getting dressed or dressing for weather of occasion; less interest in work or social relationships; and altered mood (usually more aggressive) and argumentative personality.
Alzheimer’s disease progresses in three stages marked by increasing levels of dementia. In the first stage symptoms are light and hardly recognizable. Disturbances of concentration, mental exhaustion, lack of drive and interest, fears and social withdrawal become more prominent. Greater difficulties with language -a reduction in vocabulary and a difficulty pronouncing words- and with perception also develop. Lastly however, almost all motor tasks can still be performed without any difficulty.
In the second stage this changes rapidly. Subjects become unable to perform simple everyday activities. Reading and writing skills are lost. Motor control becomes reduced, leading to increased risk of injury. Long-term memory becomes impaired and the subject may fail to recognize close relatives. This causes an inability to interact well with others as well as aggression and restlessness. It is at this stage that the majority of dementia disorders are identified.
Lastly, in the third stage the dementia becomes severe, with the subject having a complete dependence on caregivers. The subject can longer recognize home and family. Speech is reduced to simple sentences or even single words, though patients can often understand and return emotional cues and signals. Extreme exhaustion is usually present. The subjects lose the ability to feed themselves as their muscle mass and motor control deteriorates (including bladder and bowel) until they are bed ridden. Finally, death is usually caused by external factors, due to a very weakened immune system.