Alzheimer’s disease is the most common type of dementia. It is a progressive disease beginning with mild memory loss and possibly leading to loss of the ability to carry on a conversation and respond to the environment. Alzheimer’s disease involves parts of the brain that control thought, memory, and language. It can seriously affect a person’s ability to carry out daily activities. There are two main types of Alzheimer’s: familial and sporadic. Familial Alzheimer’s is a rare form that is directly linked to genetic mutations, while sporadic Alzheimer’s is more common and has a complex genetic component.
Dr Aparna Rajadhyaksha, who is a Senior Consultant – Molecular Genomics and Genetics Expert, at Metropolis Healthcare Limited said, “The prevalence of dementia in India is 7.4% among adults over the age of 60. That is, about 8.8 million Indians are currently living with dementia. By 2050, over 75% of cases of Alzheimer’s disease and related dementias (ADRD) are expected to occur in low-and middle-income countries.”
“In most cases, Alzheimer’s does not have a single genetic cause. Instead, it can be influenced by multiple genes in combination with lifestyle and environmental factors. Consequently, a person may carry more than one gene or group of genes that can either increase or reduce the risk of Alzheimer’s. People who develop Alzheimer’s do not always have a history of the disease in their families. Still, those who have a parent or sibling diagnosed with the disease have a higher risk of developing Alzheimer’s than those without that association,” she added.
Role Of Genetics In Alzheimer’s Disease:
Dr Kailas Mirche, who is a Neurologist at Citizens Specialty Hospital, Hyderabad said, “Genetics plays a significant role in the development of Alzheimer’s disease. While it is not solely a genetic disorder, a person’s genetic makeup can increase their susceptibility to the disease.”
“Mutations in certain genes, such as APP, PSEN1, and PSEN2, are associated with familial Alzheimer’s and can lead to the early onset of the disease, often in a person’s 30s to 60s. Apolipoprotein E (APOE) gene variants, particularly APOE ε4, are the most well-established genetic risk factors for sporadic Alzheimer’s. Carrying one or two copies of the APOE ε4 allele increases the risk and lowers the age of onset,” he further added.
Dr Kailas Mirche continued to say that a genetic predisposition does not guarantee someone will develop Alzheimer’s, and conversely, not having these genetic factors does not guarantee immunity. Additionally, environmental factors and lifestyle choices also play a critical role in disease development.
The Two Groups Of Alzheimer’s Genes:
Dr. Shamsheer Dwivedee, who is the Director of Department of Neurology (MIND) at Max Super Specialty Hospital, Dehradun said, “There are two groups of Alzheimer related genes – ‘At risk genes’ and ‘Deterministic genes’.
Dr. Sajid Mairaj, who is a Senior Consultant Physician and Diabetologist at Prayag Hospitals Group went on to talk about these two types of genes:
- Risk genes, like APOE-e4, increase the chances of developing Alzheimer’s but don’t guarantee it. APOE-e4 is the most well-known risk gene, and it’s estimated that 40-65% of Alzheimer’s patients have it. Having one copy of APOE-e4 from either parent raises your risk, and having two copies increases the risk even more. APOE-e4 also tends to bring on symptoms at a younger age.
- Deterministic genes, on the other hand, directly cause Alzheimer’s. If you inherit one of these genes, you will develop the disease. However, these genes are very rare and are responsible for only about 1% or less of Alzheimer’s cases. They typically lead to early-onset Alzheimer’s, with symptoms starting in a person’s 40s to 50s.
“More than 100 genes are identified as ‘At risk genes’ for Alzheimer’s disease. No point chasing them. One important defining fact about these genes is that though they put the person at risk but the person is unlikely to get the disease before 65 years of age,” Dr. Shamsheer Dwivedee further said.
“A person who wants to reduce the risk of dementia in himself and his loved ones should focus on healthy lifestyle rather than the genetics because ‘At risk gene’ effect can be negated with these habits which includes, heart healthy diet (works for Alzheimer’s prevention as well), good quality sleep, 4km of brisk walk daily and remaining mentally and socially active,” he added.
He also said that if in a person, Alzheimer’s develops before 60 years of age there are more likelihood of the person carrying the ‘definitive’ or the dominant gene namely – APP (on chromosome 21), Presenelin 1 (on chromosome 14) and Presenelin 2 (on chromosome 1). If one is carrying these genes then there is a very high chance of getting AD. But these constitutes 0.2 to 0.5 percent of AD in various populations. There is always a family history and the decline in cognitive functions starts early.
Why Is It Important To Understand These Genes?
“Understanding these genes is important because it helps us grasp the underlying biology of Alzheimer’s, especially the role of a protein called beta-amyloid. It also informs genetic testing, which can identify APOE-e4 and rare deterministic genes. But it’s crucial to note that routine genetic testing for Alzheimer’s isn’t widely recommended. Testing should come with counseling because the results can have profound effects on individuals and their families, including decisions about treatment and how they plan for the future,”said Dr. Sajid Mairaj.
One note of caution that before genetic testing a genetic counselling is advisable because partial information can cause unnecessary anxiety, fear and may lead to wrong choices in life. We do not have gene therapy for dementia. The good habits mentioned above is universally true for all types of dementia. So live healthy and stops worrying.
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