Does one need to get tested for Alzheimer’s Disease if a family member has it?

September is World Alzheimer's Month and here's what you need to know about this disease.

 |  4-minute read |   23-09-2018
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Declaring September as World Alzheimer's Month and September 21 as World Alzheimer Day was done in in 2012 with the sole intention of increasing awareness and decreasing stigma about the disease.

What is dementia?

Dementia is defined as a dysfunction of the brain, impairing multiple higher mental functions like memory, thinking, language and judgment.

Consciousness (the state of being aware of one’s surroundings) is not generally impaired in dementia. Dementia can be triggered by multiple factors, such as traumatic brain injury, vascular insults (stroke) or any other disease that affects the function of the cerebral cortex (the outer layer of the cerebrum, composed of folded grey matter that plays an important role in consciousness).

Dementia is generally mistaken as an age-related memory impairment and is generally believed to be part of the normal ageing. Age-related memory-impairment occurs in certain cases for patients above the age of 65, but it is different from dementia. With increasing awareness and availability of predictive genetic testing, more and more individuals are concerned about the risk of developing dementia, especially when a family member has been diagnosed with the same.

What is Alzheimer's dementia?

Alzheimer’s disease is one of the most common causes of dementia in the elderly, with an increasing prevalence as age advances.

Even though the German psychiatrist Alois Alzheimer identified the first case of dementia with changes in the brain as early as in 1906, it took another 50 years before the exact disease-causing mechanism for this type of dementia was identified. Patient diagnosed with Alzheimer's dementia suffers slowly-progressive memory-loss along with deterioration in language or execution.

If an individual has memory-loss and impairment in other higher mental functions, then it is essential that a neurological evaluation is done and the exact cause for dementia is ascertained. In addition to Alzheimer's dementia, there are many other causes for dementia, like Huntington's disease, Parkinson's disease, frontotemporal dementia etc.

alz_092318064821.jpgAlzheimer’s disease is one of the most common causes of dementia in the elderly.

Do I need to get tested for Alzheimer dementia?

Almost one fourth of the population above 55 years of age has, at least, one relative who suffers from dementia.

A question that is commonly asked is about the risk of developing dementia in other family members.

To answer this question, it is essential to understand the types of dementia and types of Alzheimer’s Diseases. The most common form of Alzheimer’s Disease is the late onset form where symptoms appear after the age of 60-65. Most patients who suffer from this are the only ones affected in their families. A genetic cause (where a single gene causes the symptoms is identified) is rare in such cases.

But there is a rarer form of Alzheimer’s known as early-onset Alzheimer’s Disease, where the symptoms of dementia appear before the age of 60-65. In case of multiple affected family members and more individuals with a younger age of onset of symptoms could indicate a genetic cause for Alzheimer Disease.

Such families should seek the help of trained clinical geneticists to discuss the prospects of genetic testing.

What are the types of genetic testing available for Alzheimer’s disease?

Genetic testing can be of two types. Testing can be done in symptomatic individuals in a family to look for changes in genes, which are implicated in Alzheimer’s Disease.

Testing can also be done in individuals who have not yet developed symptoms. This is called pre-symptomatic or predictive testing.

It is always advisable to go for such testing after appropriate counseling by a trained clinical geneticist. Direct-to-consumer testing for Alzheimer’s disease, offered by some private companies, should be strongly discouraged. If a genetic form of disease is suspected, the affected individual should be first tested, followed by testing for at-risk family members, after appropriate pretest and post-test counseling.

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Having an affected first-degree relative (father, mother, sibling) with Alzheimer’s Disease does not necessarily mean that there is a 100 per cent chance for developing dementia in later life.

Genetic causes account for a very low percentage of total patients with Alzheimer’s Disease. The risk of developing dementia can be as high as 50 per cent when a genetic cause is identified in a family. But in a family with a single affected individual with late-onset Alzheimer Disease, the first-degree relatives (offspring, siblings) have only a twofold increase in chance of developing dementia later in life, compared to general population.

The most important aspect is to not opt for direct-to-consumer testing in laboratories and to consult a clinical geneticist before resorting to genetic testing.

Also read: A wood-based fibre to replace fat in diet: Do we need it at all?

Writer

Dr Dhanya Lakshmi N Dr Dhanya Lakshmi N @dhanyalakshmin

The author is a medical geneticist interested in popularising science. She works as an assistant professor of medical genetics at Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad.

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