CNN
—
Researchers working to unlock the secrets of Alzheimer’s disease say they have provided important clues that could help protect people at risk for this form of dementia.
Family history shows that the man, who was destined for developing amnesia in his 40s or 50s, remained functional for decades longer than he should have. He appears to have been protected by a rare genetic change that enhances the function of proteins that help nerve cells communicate.
Scientists say understanding how this genetic change protected his brain could help prevent Alzheimer’s disease in others.
The man is part of a large family in Antioquia, Colombia, many of which inherit a mutated gene called presenilin-1 (PSEN1). Carriers of PSEN1 are almost certain to develop Alzheimer’s disease at a relatively young age.
The man, who had a PSEN1 mutation, eventually developed memory and thinking problems. He was diagnosed with mild dementia at the age of 72, after which he experienced further memory loss and infections. He died of pneumonia at the age of 74.
But apparently he had memory and thinking problems decades ago. When doctors examined his postmortem brain, they found it contained high amounts of beta-amyloid and tau, two proteins that accumulate in the brains of people with Alzheimer’s disease.
But he had something to his advantage. Genetic analysis revealed that the man had a rare change in a gene that encodes a protein called reelin, which helps nerve cells communicate.
“In this case, it was very clear that this Reelin variant made Reelin work better,” said Harvard University’s associate professor of ophthalmology and lead author of the new study on this man. said Dr. Joseph Arboleda Velazquez.
“It gives us great insight,” he said. “It’s very clear that just injecting more Reelin into the brain can actually help patients.”
of research published Published in Nature Medicine on Monday.
The enhanced Reelin protein appears to protect a very specific part of the male brain: an area called the entorhinal cortex, located at the base of the brain behind the nose.
“Another big insight from this case is that you probably don’t need this anywhere in the brain,” said Arboleda Velázquez.
The entorhinal cortex is especially sensitive to aging and to Alzheimer’s disease. This is also the area of the brain that sends and receives signals related to smell. Loss of the sense of smell is often a precursor to brain changes that lead to memory and thinking difficulties.
“So when people get Alzheimer’s disease, it starts in the entorhinal cortex and then spreads,” says Arboleda Velázquez.
This is the second time Arboleda Velázquez and the team studying this extended family have found someone who defies genetic odds.
In 2019, scientists reported the incident The story of a woman who would have developed Alzheimer’s disease early, but instead retained her memory and thinking ability into her 70s.
She had two altered copies of the APOE3 gene called the Christchurch mutation. It appears that the activity of the APOE3 protein was reduced. Like Reelin, APOE is a signaling molecule known to play a role in shaping Alzheimer’s disease risk.
It turns out that there is a connection between these two cases. Reelin’s cellular receptor is the same as that of APOE.
“So these two patients are pointing at something like a big arrow. They’re telling us, ‘Hey, this is the trail.’ This is an important pathway to maximally prevent Alzheimer’s disease,” said Arboleda Velázquez.
However, this route may not be as protective for everyone. The man’s younger sister in the new study also shared a rare defense gene change, which helped her, but not by much. According to her family, she began experiencing her cognitive decline at the age of 58.
Professor Arboleda Velázquez said it may be because women make less of the Reelin protein as the gene becomes less active as they age. “They may have a variant, but they don’t express it as much as men do,” he said.
A Harvard team says it is already working to develop treatments based on these findings.
Richard Isaacson, Ph.D., a preventive neurologist at Florida Atlantic University, says studies like this show something important: “In some cases, you can win the tug-of-war with your genes.”
Does this mean a cure is just around the corner? I don’t know yet.
“Can we use research like this to transform and improve care? I hope so. We’re not there yet.” Not Isaacson said. “But I think it’s an important study.”
