Genetic Risk Factors for Alzheimer’s Predicted in Young Adults

Genetic testing might predict the risk of developing Alzheimer's disease even before symptoms occur; probably in healthy young adults.

Genes may play a significant role in the development of dementia.
Though the genes associated with Alzheimer's have been identified, it is still tough to predict people who are at risk of developing this disease.
A new genetic test could predict who are at higher risk of developing Alzheimer’s disease even before symptoms appear; possibly in healthy young adults too.

Alzheimer’s Disease (AD), one of the common forms of dementia affects 47 million people in the world. Most of the people affected with Alzheimer's disease consider that they have inherited the condition from their parents.

Facts you should know about Alzheimer’s Disease

Every 66 seconds someone in the United States develops Alzheimer’s
One in three old-aged people dies with Alzheimer’s or another form of dementia
The cost of caring for patients with Alzheimer’s is estimated to be $236 billion in 2016
In India more than 4 million people have some form of dementia.

Genetic link of Alzheimer’s has been extensively studied and previous researchers have highlighted that genes do play a significant role in the development of dementia. There are two forms of Alzheimer's disease - rare Early Onset and common Late Onset.

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The apoE4 protein changes the activity of neurons in the hippocampus - an important memory center in the brain that is severely affected by Alzheimer's disease.

‘Genetic risk of Alzheimer's disease may exert an effect on the hippocampus region of the brain very early in life. This can make these individuals more susceptible to Alzheimer's disease later in life.’

Early onset is when the symptoms of the Alzheimer's disease appear before the age of 65 and late onset is when the symptoms typically develop after this age. But these two types have different patterns of genetic inheritance.

Early Onset of Alzheimer's disease (EOAD) is due to mutations in three genes, amyloid precursor protein (APP) gene and two presenilin genes (PSEN-1 and PSEN-2). Mutations in these genes can trigger the development of dementia in the age of 30 or 40 years, but it is very rare.

Late Onset of Alzheimer's Disease (LOAD) is very common and it is attributed to mutations in one gene called the apolipoprotein E (APOE). Though the genes associated with Alzheimer's have been identified, it is still tough to predict people who are at risk of developing this disease.

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Alzheimer's disease is a progressive neurodegenerative disease affecting memory and thinking and making the person increasingly dependent on others.

A study recently published in the journal Neurology, the medical journal of the American Academy of Neurology reported that a genetic score could predict who are at higher risk of developing Alzheimer’s disease even before symptoms appear; possibly in healthy young adults too.

The Research team from the Massachusetts General Hospital calculated polygenetic risk scores (PGRS) using data from the International Genomics of Alzheimer's Project.

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They examined 166 older patients with dementia and 1026 patients without dementia for identifying an association between PGRS and certain Alzheimer's markers such as cognitive decline, clinical progression, hippocampus volume, and β-amyloid, while 1,322 healthy young adults between 18-35 years were assessed for an association between PGRS and hippocampus volume.

They found that a higher PGRS was associated with poor memory and smaller hippocampus region in older patients without dementia at the start of the study. Over a period of three years, the researchers found that higher PGRS was also associated with cognitive decline and clinical progression of the disease.

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Each standard deviation increase in polygenic risk was associated with a 1.6 times increase in the risk of clinical progression of Alzheimer's.

Among the healthy young adults, the study noted that a higher progenetic risk score was associated with smaller hippocampus volume. Furthermore, researchers found that healthy adults who had more genetic variants had developed mild cognitive impairment; later progressing into Alzheimer’s disease.

Hippocampus region of the brain deals with learning and memory and this undergoes critical damage in early stages of Alzheimer's disease. Therefore, shrinking hippocampus signals the start of Alzheimer's.

“Our study was small and larger numbers of participants will need to be studied to confirm our findings. The goal of this type of research is to help physicians better identify those at high risk of dementia so that future preventative treatments may be used as early as possible,” said Elizabeth C. Mormino, Massachusetts General Hospital.

References:

Elizabeth C. Mormino, Reisa A. Sperling, Avram J. Holmes, Randy L. Buckner, Philip L. De Jager, Jordan W. Smoller, Mert R. Sabuncu; Polygenic risk of Alzheimer disease is associated with early- and late-life processes; Neurology 2016; 10.1212/WNL.0000000000002922.
Genetics of Dementia - (https://www.alzheimers.org.uk/factsheet/405)
Alzheimer's & Dementia: Global Resources - (https://alz.org/global/)
Alzheimer's and Dementia in India - (http://www.alz.org/in/dementia-alzheimers-en.asp)

Source-Medindia