Alzheimer’s, one of the most progressive neurodegenerative diseases, impacts millions across the globe. Lifestyle factors and other environmental elements contribute to this disease, but genetics play a significant role. Genetic testing can give people insight into their inherent dispositions and risk profiles for developing Alzheimer’s, especially in those with a family history. WHO reports that Alzheimer’s disease is the most common form of dementia and may contribute to 60–70% of cases worldwide.
Who should consider genetic testing?
Genetic testing is also recommended for individuals with a family history of Alzheimer’s disease, especially if those affected were diagnosed before the age of 65. Genetic Alzheimer’s tends to begin early in life; however, a test may allow a level of assessment of the degree of risk. This can be very useful if diagnosed within the first line of relatives. APOE-e4 is the most common gene associated with Alzheimer’s, but it does not guarantee the development of the disease. Approximately 20%–25% of those suffering from Alzheimer’s have this genetic disposition. In India, there are about 8.8 million citizens over 60 who are diagnosed with dementia, which gives some indication that genetic clues can contribute to future planning and prevention strategies. The rising incidence of dementia, including Alzheimer’s, necessitates a dedicated focus on spreading awareness and early intervention.
What does genetic testing reveal?
Genetic testing typically identifies two types of genes:
APOE-e4: The most common gene implicated in Alzheimer’s is best described as APOE. There is a proven association between a copy or two of the APOE-e4 gene and the prevalence of risk, but again, it does guarantee the development of Alzheimer’s. People can possess one or two copies of this gene; the risk of developing the disease is directly proportional to the number of copies. Many people inherit the gene but never develop Alzheimer’s, while others without the gene may still develop the disease or other forms of dementia later in life.
PSEN1, PSEN2 and APP: These are associated with familial Alzheimer’s disease (FAD), accounting for early-onset Alzheimer’s in only a few percent of all cases. Mutations in these genes ensure that Alzheimer’s will be expressed if the genes are inherited, often under the age of 65. Though these mutations occur infrequently, they have a near 100% chance of resulting in the disease if passed down.
Benefits and limitations of genetic testing
Genetic testing can give valuable insight into the absence or presence of an inherent disposition for Alzheimer’s. A positive result may promote a change in lifestyle towards improving cardiovascular health and cognitive activities that would hold off the onset of the disease. Additionally, it helps in preparing, emotionally and financially, for what’s to come. However, genetic testing has its limits: a positive result, such as for the APOE-e4 gene, doesn’t guarantee the development of the disease, and a negative result does not rule out the risk of developing it. Apart from this, a positive result may also cause considerable emotional stress; thus, genetic counselling is required to aid and assist the individuals in understanding and managing the results. In India, generally, the disorder’s prevalence is higher in rural areas and among women; hence, genetic testing needs serious consideration with regard to available care and support systems.
Takeaway
Genetic testing is necessary for those who have a family history of Alzheimer’s, but it should be approached with due caution and proper guidance. For the Indian population, as the incidence of Alzheimer’s increases, it will become an important adjunct to overall preventive health measures in the way of helping families prepare for care and understanding their risks better. Utilizing genetic information responsibly will enable individuals to be more prepared while looking for early interventions that will possibly delay the onset of symptoms.
(The author, Dr. Shelly (Mittal) Mahajan, is the Lab Director & Clinical Lead at Mahajan Imaging Labs.)
