16 Common Causes of Alzheimers Disease

Alzheimer’s Disease is a degenerative brain condition that causes the brain cells to die. It is also one of the primary causes of dementia in older adults. The development of Alzheimer’s disrupts language, reasoning, perception, and thinking skills. The symptoms start as general forgetfulness and progress to interfere with the ability to carry out daily activities. People aged over 65 years are commonly affected by Alzheimer’s.

The exact reason for the development of this cognitive ailment still remains unknown. As per medical professionals the causes of Alzheimer’s disease could be a combination of multiple factors including age, family medical history, certain congenital conditions, etc. The changes in the nerve cells of the brain also lead to the development of the condition.

As such, the only way to know what causes of Alzheimer’s disease is to conduct diagnostic tests to analyse the brain condition. It should also be noted that there is no effective cure for Alzheimer’s. But once the root cause is identified, doctors can suggest medications and therapies to manage the symptoms and control the disease from progressing.

Genetic Influence on Alzheimer’s Disease

In rare cases, Alzheimer’s occurs due to genetic mutations. When this happens, the condition is known as familial Alzheimer’s disease (FAD). Three genes – amyloid precursor protein (APP), Presenilin 1 (PSEN1) and Presenilin 2 (PSEN2) influence the development of Alzheimer’s disease. They mutate and produce amyloid-peptide excessively. Over time, such production creates a toxic build-up and leads to the death of nerve cells.
Another gene associated with the risk of Alzheimer’s is apolipoprotein E (APOE) on chromosome 19.

One of its several forms, APOE-e4 is strongly linked with the development of late-onset Alzheimer’s. Having this gene variation does not guarantee the onset of the disease, but it increases the risk. It promotes the build-up of the structures called amyloid plaques in the brain. A patient with Alzheimer’s can inherit APOE-e4 from either of the parents. When inherited by both parents, the risk increases, especially in individuals aged younger than 65 years.

What Causes Alzheimer’s Disease?

Some of the risk factors that influence the development of Alzheimer’s disease are:

• Age: Age is the most significant factor that increases the risk of Alzheimer’s. Although disease development is not a normal part of ageing, in most cases, people aged over 65 years are likely to get diagnosed. The risk doubles every five years one crosses the age of 65 years. In rare scenarios, younger people also suffer from Alzheimer’s. The earliest signs are noticeable between 35 to 40 years of age. Such early development is known as early-onset Alzheimer’s.

• Family Medical History: If your immediate relatives like your parents or siblings have had Alzheimer’s, your risk of developing the disease increases. However, having a family history of the condition does not guarantee its onset. The influence depends on the changes or mutations in genes that trigger Alzheimer’s. The genetic risk factor is minimal but cannot be ignored to find the root cause. It is the main cause of familial Alzheimer’s, which is directly related to the hereditary inheritance of abnormal genes.

• Down Syndrome: The known causes of Alzheimer’s disease also includes Down Syndrome. Down Syndrome is a genetic chromosome disorder where there is an extra copy of chromosome 21. The additional gene in chromosome 21 excessively produces amyloid precursor protein (APP). The higher amount of APP leads to the formation of clumps called beta-amyloid plaques in the brain which impact the normal functioning of the nerve cells. Such abnormal activity increases the risk of developing Alzheimer’s. Per a report by the Centre of Disease Control and Prevention and the National Down Syndrome Society, approximately 30% of Down Syndrome patients in their 50’s have Alzheimer’s, while 50% of patients develop the condition in their 60s.

• Deficiency of Brain Chemicals: Alzheimer’s disease is caused by a deficiency of the neurotransmitter, acetylcholine (Ach) It is an organic chemical in the brain essential for processing memory and learning. The low presence of acetylcholine causes neurological problems. It gives rise to symptoms of memory loss and as the deficiency increases, problems advance to disorientation, mood swings, behavioural inconsistencies, etc. All these signs are associated with Alzheimer’s disease.

• Cardiovascular Conditions: The brain cells receive protein and oxygen via the blood pumping in the cardiovascular system. This natural body function creates a heart-head connection. When the heart condition is affected due to ailments like high cholesterol, high blood pressure, cardiovascular disease, etc., nutrient supply to the brain gets impaired. As a result, there is an inadequate blood supply to the brain which causes cerebral hypoperfusion, which is known to contribute to amyloid plaques and cause Alzheimer’s.

• Gender: Life expectancy is higher in women than men. As age influences the onset of Alzheimer’s disease, longer life expectancy makes women more susceptible to the disease. Besides life expectancy, sex chromosomes, brain structure, hormones, etc., also play a role in developing Alzheimer’s. Another factor is the development of amyloid plaques in women due to their stronger immune systems compared to men. These causes are a possibility, and more research is needed to confirm the gender dynamics.

• Head Injuries: Moderate and severe traumatic brain injuries are linked to the onset of Alzheimer’s. The evidence for the same is low and the research is still underway. But the basis of the association between brain injury and Alzheimer’s disease is the effect on brain function. Years after sustaining a traumatic brain injury, the person becomes susceptible to cognitive decline and develops Alzheimer’s disease. Additionally, the presence of the apolipoprotein E (APOE) variant called APOE-e4 increases the probability greatly.

• Social Isolation: Social isolation is linked to shrinkage in certain parts of the brain that affect the cognitive response. Being socially cut off also increases depression and loneliness. Such stressors deteriorate brain function in the long run. Alzheimer’s disease is caused by this functional effect on the neurological system. The risk factor of limited social engagement is fixable in the early years through active participation in social activities.

• Environmental Triggers: Our environment has a great deal of influence on our physical and mental well-being. Certain environmental factors like the toxic chemicals exposed due to air and water pollution, give rise to neurodegenerative disorders. Some other chemicals are present in pesticides, food additives, and organic pollutants that enter our bodies. Such exposure can cause chemical changes in the brain and manifest into memory loss and other cognitive defects in older age.

• Hearing Loss: The brain tissue gets damaged and the brain structure changes with time when the ‘hearing’ section is inactive. Such abnormality is one of the causes of Alzheimer’s disease. In addition, difficulty in hearing gives rise to a phenomenon called brain overload. As a result, the person suffering from hearing loss struggles mentally and there is a strain on the brain power needed for cognitive functions like remembering, thinking, and learning information.

• Lifestyle Habits: Alzheimer’s disease is caused by certain lifestyle habits as well. Lifestyle habits directly contribute to the development of various diseases in old age. The main factors linked to memory loss and decline in cognitive function are a sedentary lifestyle, obesity, improper nutrition, etc. Other habits include exposure to toxic substances like tobacco and alcohol.

• Uneven Sleep Cycle: Sleep deprivation increases the levels of beta-amyloid in the brain. The abnormal level of this neuroprotein leads to the creation of amyloid plaques. The changes also take place in the thalamus and hippocampus in the brain. These areas are particularly vulnerable to damage. When they get affected due to lack of sleep or disrupted sleep patterns, cognitive abilities like thinking, learning, and memorising are adversely affected and may manifest into Alzheimer’s later.

Biological Processes in the Brain Causing the Development of Alzheimer’s

Molecular changes take place in the brain throughout our lives. But some of them lead to cell damage and act as causes of Alzheimer’s disease, including the following:

• Amyloid Plaques: The brain contains a protein called amyloid-beta or A-beta. It comes in different molecular forms that may collect between neurons as a result of the breakdown of a larger protein, amyloid precursor protein. When amyloid beta lodges between neurons, it leaves deposits called amyloid plaques between the brain cells. Over time, these plaques travel to other regions of the brain, including the hippocampus, which affects memory function. When amyloid plaques grow larger, they block signals between brain cells, leading to cognitive decline. The outcome is the development of Alzheimer’s.

• Neurofibrillary Tangles: The abnormal accumulation of a protein called tau inside neurons gives rise to neurofibrillary tangles. They affect the normal function of tau, which usually binds and stabilises microtubules – internal structures that guide nutrients and molecules from the cell body to axons and dendrites. When the microtubules fail to carry out their function, the neurons’ transport system gets negatively affected. The eventual outcome is the death of brain cells, which leads to the first sign of memory loss, leading to Alzheimer’s.

• Brain Shrinkage and Inflammation: The surface layer that covers the cerebrum withers and shrinks due to abnormalities in neurological function. Such damages cause havoc and affect the brain’s normal activity like the ability to recall, focus, and plan. Another effect on the brain’s normal functioning is inflammation. The brain has glial cells, meant to clear debris and destroy toxins. When the brain contains beta-amyloid plaques, a type of glial cell, microglia mistake it as a cell injury and stimulates an immune response. The result of this overdrive is chronic inflammation, which damages the brain cells and causes Alzheimer’s.

• Loss of Connection: Brain functions like memory and thinking depend on the signal transmission between neurons in the brain. When you develop the complexities associated with cognitive disorder, signal transmission between cells gets interfered. The activity of brain chemicals like neurotransmitters also gets affected. Due to the disturbed chemistry occurring from flawed signalling, the message transmission between brain cells is lost. Such loss of connection leads to the onset of Alzheimer’s disease.

Diagnostic of Alzheimer’s Disease

As is apparent, there are no definite causes of Alzheimer’s disease, except for risk factors and neurological disorders. Thus, the diagnosis of this illness affecting cognitive abilities involves studying the brain process. Some tests conducted for the same include:

• Physical examination and laboratory testing of blood and urine samples.
• Neurological exams test reflexes, muscle coordination and strength, speech, eye movements, and sensation.
• Brain imaging tests like computed tomography (CT) scan, magnetic resource imaging (MRI) scan, and/ or positron emission tomography (PET).
• Cognitive, functional, and behavioural tests that analyse thinking and memory skills.
  Mood and depression assessment tests.