Researchers have found that people who have two copies of a specific gene develop almost all the signs of Alzheimer’s disease, which may represent a distinct genetic form of the condition. Although scientists knew that the APOE4 gene was linked to an increased risk of Alzheimer’s, a new study suggests that in people who carry two copies of the gene, it is an underlying cause of the disease. Euronews.
Published in Nature Medicine, the study also found that people with two copies of the gene develop the disease earlier than people with other variants of the APOE gene.
Alzheimer’s disease is the most common form of dementia and affects around 7.8 million people in the European Union. Its characteristic symptoms include a decline in memory function and thinking skills.
The findings mark a distinction with “profound implications,” said Dr. Juan Fortea, the study’s lead author at the Sant Pau Research Institute in Barcelona, Spain.
An estimated 15 percent of Alzheimer’s patients carry two copies of the gene, meaning these cases “can be traced back to a cause, and the cause is in the genes,” Fortea said.
“This gene has been known for over 30 years and was known to be associated with a higher risk of developing Alzheimer’s disease,” he added in a statement.
“But now we know that virtually all people with this duplicated gene develop Alzheimer’s biology. This is important because they represent between 2 and 3 percent of the population.”
The scientists say these findings mean it is critical to develop treatments that target the APOE4 gene.
What is the connection between genetics and Alzheimer’s disease?
A handful of genes are known to cause rare forms of “early-onset” Alzheimer’s, mutations passed down in families that trigger symptoms at an unusually young age, for example as young as 50. Some cases are also linked to Down syndrome.
But Alzheimer’s is most common after age 65, especially in the late 70s and 80s, and the APOE gene, which also affects how the body handles fat, has long been known to play a role.
There are three main variants. Most people carry the APOE3 variant, which does not appear to increase or decrease the risk of Alzheimer’s. Some carry APOE2, which offers some protection against Alzheimer’s.
APOE4 has long been labeled as the biggest genetic risk factor for late-life Alzheimer’s, with two children more at risk than one.
“Familial form of Alzheimer’s disease”
Fortea’s team used data from 3,297 brains donated for research and from more than 10,000 people who participated in American and European Alzheimer’s studies.
They examined early symptoms and signs of Alzheimer’s, such as amyloid in the brain.
People with two copies of APOE4 accumulated more amyloid by age 55 than those with a single copy or the “neutral” variety of the APOE3 gene, they said in the study.
By age 65, brain scans showed significant plaque buildup in nearly three-quarters of these double carriers, who were also more likely to have initial Alzheimer’s symptoms around this age rather than at 70 or 80 years.
Fortea said the underlying biology of the disease was remarkably similar to the young inherited types.
It seems more like “a familial form of Alzheimer’s,” said Dr. Eliezer Masliah of the National Institute on Aging. “It’s not just a risk factor.”
Masliah said other research is aimed at developing gene therapy or drugs to specifically target APOE4.
He said it’s also critical to understand the effects of APOE4 in diverse populations because it has been studied mostly in white people of European ancestry.
But study co-author Dr. Reisa Sperling, of Harvard-affiliated Brigham and Women’s Hospital in Boston, said the news doesn’t mean people should rush for a genetic test.
“It’s important not to scare everyone who has a family history” of Alzheimer’s because this gene duo is not behind most cases, she told The Associated Press.
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Tags: Study finds distinct genetic form Alzheimers disease people copies specific gene develop signs disease
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