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Role of Genes in Alzheimer’s Disease & Its Causes, Symptoms, Treatment

Alzheimer’s disease affects all the major functions of the brain. It alters negatively in calculative operations, reasoning, and decision making and instills forgetfulness and loss of memory. In this article, we look at the role of genes in Alzheimer’s disease.

Due to its course, Alzheimer’s can bring about behavioral and mental changes. Personality changes are also observed on prolonged exposure to this disease. Restlessness, loss of skills, agitation, impairments in daily routine work are all common symptoms of Alzheimer’s disease.

Role of Genes in Alzheimer’s Disease

Role of Genes in Alzheimer’s Disease

Presently Alzheimer’s affects more than 5 million Americans.1 Alzheimer’s is neurodegenerative by nature and affects mainly the older beings between the mid-60s. It can be categorized into two categories: Early-onset Alzheimer’s showing up at tender ages and Late-onset Alzheimer’s appearing during the old age. The life expectancy is of around 3-9 years. The reason for around 70% of the cases was they inherited Alzheimer’s disease from their first-degree relative. It starts after the age of 65 years.

Researchers from all around the globe concluded that a particular gene called PSEN1, on being mutated, triggers the quick and early onset of Alzheimer’s disease. Although the early footprint of this disease is observed in very few patients suffering from this disease, most of the Alzheimer’s patients who have reported themselves before retirement age are caused due to mutation occurring in this particular gene.

Two types of decisive genes decide whether an individual develops the disease or not. They are:

Risk Genes: These genes somehow increase the chances of disease development but do not guarantee it. APOE e4 is the first discovered risk gene that accounts for the highest increase in the chance of disease development. About 40-60 percent of the disease experiencing individuals carry APOE-e4 as the major risk enhancer and the reason behind their disease.

Deterministic Genes: Genes that guarantee the disease development. Familial Alzheimer’s disease (FAD) is a result of deterministic gene affection.

Early footprints or early occurrence of Alzheimer’s are caused due to inherited genetic disorders. A father or mother who might be carrying Alzheimer’s disease accounts for almost 50% of the chance to share the disorder to his child through the biological process of inheritance and heredity.2 Due to these factors, the child is more prone to Familial Alzheimer’s Disease (FAD). Single-gene mutations in chromosomes number 1, 14, and 21 set up the base for the early occurrence of this disease. Alteration in chromosome 14 shares abnormal Presenilin 1 to the inside of the brain whereas if chromosome 1 is altered, it alters the production of Presenilin 2. Chromosome 21 holds for the secretion of Amyloid Precursor Protein (APP).

Late-onset of Alzheimer’s, at the age of mid-60s and 70s, is found to have several causing factors involved, including genetic problems, lifestyle factors, environmental factors, and orthodox aging problems. As concluded by the researchers to date, no particular gene is found that causes or tends to cause the onset of Alzheimer’s at old age.

However, a protein called apolipoprotein E (APOE), in chromosome 19 is suspected to propel the increment of risk to be affected by Alzheimer’s, during the period of retirement. The APOE gene instructs the brain for the production of the apolipoprotein.

The apolipoprotein E is present in various forms that may be called as alleles:

  • APOE e2: The rarest form of APOE that in general may show some kind of resistance to Alzheimer’s disease.
  • APOE e3: An allele that shows neutral interaction towards Alzheimer’s. A ‘Neither propel, nor restrict’ type allele.
  • APOE e4: The allele that accounts for most of the propelled cases of Alzheimer’s disease. APOE e4 increases the risk of developing Alzheimer’s at a tender age and during late years. Though an individual carries 0-2 of this type of alleles, as the figure increases, there is a simultaneous high increase in the risk of disease development.

Several other genes associated with late-onset type Alzheimer’s are being figured out. Some of them are:

CLU: This gene takes up the responsibility for the clearance and removal of the coagulated amyloid peptide. Alteration in this particular gene leads to excess accumulation of the disease-causing amyloid. Imbalances in the elimination of peptide contribute to the increased risk factor.

CR1: A type of gene that regulates the production of protein inside the brain. Malfunctioning of this ABCA7 gene results in the deficiency of protein production that causes inflammation in the brain. Inflammation elevates the risk of disease development.

PICALM: This very gene manages the communication and interaction of the nerve cells among each other. In case the gene ceases to work, communication between the nerve cells is lost which accounts for disturbances in brain activities. Memory loss and common dementia are a result of impairment in this gene.

Genes like ABCA7, PLD3, TREM2, and SORL1 are also linked to higher chances of Alzheimer’s development.

An individual with an extra copy of chromosome 21, known as Down’s syndrome, has a higher risk of the development of Alzheimer’s disease.1 Extra numbers of chromosomes related to the increased number of APPs that in turn relates to much more production of amyloid peptides which radically increases the chances of disease development. All those who carry this gene don’t necessarily carry the risk factor usually. The case of disease development through this gene applies to only a few of the cases, as far as the conclusions laid by the researchers.

Stages of Alzheimer

Alzheimer’s proceeds through various stages before it completely develops itself into its host:

It has some preclinical time, before the appearance of any symptom that will indicate the presence of Alzheimer’s.

After the first stage of symptoms, are the mild symptoms, these symptoms are a little cognitive impairment which may be observed at times in this phase of the symptom.
At the last phase of Alzheimer symptoms of dementia can be observed in the patient, showing up symptoms like memory loss and forgetfulness also occurs in this phase.

Causes of Alzheimer

The risk factors point towards the role of genes in Alzheimer’s disease. If it shows up at a very young age then it is believed that it is mainly caused due to gene mutations, genetic alteration or through heredity and inheritance.

When the patient goes through an autopsy check-up, it is found that the patients have tiny deposits in their brain tissue. This disease is caused by the accumulation of a toxic protein called Beta-Amyloid peptide, in the brain, which builds up itself in the form of tiny nodules which in general term are referred to as tangles and plaques. This protein coagulates to form clumps of amyloid plaques that bring about the alteration in genes like APP (Amyloid Precursor Protein), PSEN1 or PSEN2 which in turn lead to mental disorders. These lumps of plaques force the nerve cells to separate and die, showing the orthodox characteristics of Alzheimer’s disease.

The amyloid plaques unite in the brain to form neurofibrillary tangles. Tangles like these account for the improper functioning of the brain. These tangles occur inside the nerve cell due to the presence of protein in the patient’s body known as Tau. The cause of this disorder hasn’t been yet figured out by the researchers and they believe that different circumstances cause this disorder. A gene called APOE-e4 accounts for the peak changes in the development of Alzheimer’s in older age.

Diagnosis of Alzheimer

A timely diagnosis of Alzheimer’s is necessary to plan proper treatment. Some of the diagnostic tests include

  • Fluorodeoxyglucose (FDG) PET: It helps in the identification of degenerative areas of the brain with a low metabolism. It also helps in differentiating Alzheimer’s disease with other types of dementia.
  • Blood Test: It helps to see other reasons for memory loss like vitamin deficiencies.
  • MRI Scan: It uses magnetic fields and radio waves which creates detailed images of the brain.
  • CT scan: It creates cross-sectional images of the brain with its advanced x-ray technology.

Treatment for Alzheimer’s disease

Alzheimer’s medications can help to improve the disease. Some types of medications include:

  • Cholinesterase inhibitors: It helps in improving cell-to-cell communication by safeguarding a chemical messenger, which is drained because of Alzheimer’s disease.
  • Memantine: It works by reducing the development of symptoms. Sometimes it can cause side-effects like confusion or dizziness.
  • Curcumin: It contains anti-inflammatory and antioxidant elements, which improve chemical processes inside the brain.

Some other treatments may help to improve general well-being and overall brain health. Social activities and meetings can also help the patients to feel better and improve their well-being. Healthy nutrition, a balanced diet, and adequate water are essential. Adequate sleep, calm environment and relaxation help to soothe the nerves.

Avoid caffeine as it can interfere with sleep and can disrupt the sleep cycle. A high caloric diet is also preferred. Exercise regularly as it helps improve overall health and sleep.

Anti-depressants can be used for irritability or mood swings. Anti-psychotics for delusions or aggression. Anxiolytics to control anxiety.

Genetic Testing and Treatment

The reversal of the death of nerve cells is practically impossible. Genetic tests are available for the identification of Alzheimer’s disease. As the role of the gene in Alzheimer’s disease is clear, genetic testing can prove to be of great help. However, these are best done by an expert and only if advised by your physician. Individuals carrying APOE4 may or may not get affected by this disease. The development is not guaranteed. They may also enquire about the person’s neurological function, for example, they may go for a mental check-up to know the brain balance, senses, and reflexes

Treatment of Alzheimer’s through medication and drug treatment is not available till now and is yet to be discovered. Few medicines may reduce the effect of symptoms. These include Donepezil (also known as Aricept), Rivastigmine (aka Exelon), and Tacrine (commonly called Cognex).

Researchers and the core doctors in this field conclude that many more genes linked with this type of disorder are yet to be discovered.

Tips for Coping with Alzheimer

  • Take adequate rest
  • Keep the environment calm
  • Maintain comfortable situations
  • Avoid being argumentative
  • Try to avoid things which can harm the health
  • Be involved with friends and family and participate in enjoyable activities.

While there is a lot of discussion on the role of genes in Alzheimer’s disease, good nutrition, fitness, and emotional well-being can help to protect your health.


Also Read:

Sheetal DeCaria, M.D.
Sheetal DeCaria, M.D.
Written, Edited or Reviewed By: Sheetal DeCaria, M.D. This article does not provide medical advice. See disclaimer
Last Modified On:March 6, 2020

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