In Preventing Alzheimer’s, Mutation May Aid Drug Quest
By GINA KOLATA
Published: July 11, 2012
A study of a rare gene mutation that protects people against Alzheimer’s disease
 provides the strongest evidence yet that excessive levels of a normal 
brain substance, beta amyloid, are a driving force in the disease — 
bolstering hopes that anti-amyloid drugs already under development might
 alter the disease’s course or even prevent it.        
DeCode Genetics stored blood samples from its research on genomes and Alzheimer’s disease.                            
So far, the drugs have not succeeded. But scientists not connected with 
the new study said it suggested that the drug companies’ big bets on 
anti-amyloid treatments could yet pay off.        
The implication for drug development “is hugely important,” said Dr. 
David Altshuler, a genomics expert at Harvard Medical School and the 
Broad Institute of Harvard and M.I.T. 
And Dr. Samuel Gandy, an Alzheimer’s researcher who directs the Mount 
Sinai Center for Cognitive Health, called the finding the most 
significant in the field in two decades, since researchers first 
reported a mutation that leads to the disease. 
The protective mutation, whose discovery was reported online
 Wednesday in the journal Nature, is highly uncommon — it is not the 
reason most people do not develop Alzheimer’s. But what intrigues 
researchers is how it protects the brain. 
Mutations that cause Alzheimer’s lead to excessive amounts of beta 
amyloid in the brain; by contrast, the protective mutation slows beta 
amyloid production, so people make much less.        
“This paper provides strong evidence that it would work in the general 
population if you did it right,” Dr. Altshuler said. 
Scientists at the drug companies agreed. “We are thrilled,” said Ryan 
Watts, one of the authors of the new paper and head of the 
neurodegeneration labs at Genentech, which is developing two drugs to 
reduce brain amyloid levels. 
Dr. Richard Mohs, leader of neuroscience early clinical development at 
Eli Lilly, said the company was “very encouraged by these study 
results.” They show, he said, that despite an initial failure, the 
strategy of focusing on drugs to reduce beta amyloid levels is “a 
logical path for the development of effective therapies that may slow 
disease progression.” 
Many questions remain, of course. Most people do not have the protective
 gene mutation, but as common as Alzheimer’s is, most people do not get 
it. It is not clear why. And most who develop Alzheimer’s do not have 
one of the rare gene mutations that cause it. The reasons for their 
disease are unclear. 
The discovery of the protective gene mutation, a product of the revolution that has taken place in genetics, arose when researchers scanned the entire DNA of 1,795 Icelanders. 
About 1 in 100 had a mutation in the gene for a large protein that is 
sliced to form beta amyloid. Then the investigators studied people who 
had been given an Alzheimer’s diagnosis, and a group of people 85 and 
older. Those with the mutation appeared to be protected from Alzheimer’s
 disease.        
The investigators, led by Dr. Kari Stefansson, chief executive at DeCode
 Genetics, an Icelandic company, looked at genomes of North Americans 
and found the gene mutation in only about 1 in 10,000 people. That 
indicates, Dr. Stefansson said, that the mutation arose relatively 
recently in Scandinavia. 
The protective gene even appears to override a very strong risk factor 
for Alzheimer’s disease in old age — two copies of a gene known as 
ApoE4. Ninety percent of people with two ApoE4 genes get Alzheimer’s by 
age 80. But Dr. Stefansson says there are 25 people in his study with 
two copies of ApoE4. None have Alzheimer’s disease. 
The research “is obviously right,” said John Hardy, an Alzheimer’s 
researcher at University College London and a discoverer of the first 
gene mutation found to cause the disease. “The statistics and the 
finding are pretty secure.” 
The discovery is part of a continuing story that implicates beta amyloid
 as a central and crucial player in this destructive brain disease. The 
idea began two decades ago with the discovery of very rare gene 
mutations that always cause Alzheimer’s in those who inherit them, 
usually by middle age. The mutations were different in different 
families, but all had the same effect: They increased the amount of beta
 amyloid in the brain. That meant that a buildup of amyloid was 
sufficient to cause the disease.        
Elderly people with Alzheimer’s — who typically do not have these gene 
mutations — also had excess amyloid in the brain. So researchers 
reasoned that might mean that excess amyloid was causing the disease in 
them, too. 
Additional evidence
 of the role of beta amyloid was reported on Wednesday in The New 
England Journal of Medicine. Using spinal taps and brain scans to track 
the protein, investigators found that people with one of the 
Alzheimer’s-causing mutations start making too much beta amyloid as long
 as 20 years before they have symptoms of the disease. 
Researchers and drug companies focused on the amyloid hypothesis to the 
extent that almost every experimental drug being tested to slow or halt 
Alzheimer’s disease is designed to reduce the amount of amyloid in the 
brain. Most of those drugs are still being tested in clinical trials, 
but a Lilly drug that failed spectacularly in 2010, semagacestat, 
actually made people with Alzheimer’s worse and gave rise to 
soul-searching in the field. 
It emphasized a crucial question that hung over the endeavor. Was 
amyloid really causing Alzheimer’s in elderly people? Might the protein 
instead be a bystander, accumulating, for example, as part of the 
brain’s response to damage? 
The discovery of the protective gene mutation provides strong clues. 
People with the mutation make substantially less beta amyloid, but other
 than that they are no different from anyone else. And they do not get 
Alzheimer’s. 
People could be tested to see if they have the protective mutation, Dr. 
Stefansson said, but he added, “The benefits of doing so are not obvious
 to me.” He explained that since the gene is so rare, chances that a 
person being tested would have it — especially if that person is not 
Scandinavian — are extremely low. Almost everyone would end up with the 
same uncertainty they have now. There is as yet no way to prevent 
Alzheimer’s and, outside of families with one of the rare 
disease-causing gene mutations, no way to know who is going to get it. 
Still, Dr. Hardy noted, as provocative as the discovery of the 
protective gene mutation is, the strategy of reducing amyloid levels — 
the ultimate test of the amyloid hypothesis — still must be evaluated in
 typical Alzheimer’s disease. For example, perhaps people need to have 
lower levels of beta amyloid from birth to really be protected. 
Researchers and companies explain away the failure of the first few 
experimental drugs to reduce beta amyloid levels or to block the protein
 by saying they were not powerful enough and were studied in people who 
already had the disease and clear symptoms of mental decline. By then it
 might be too late to make any difference. When brain cells have died, 
nothing can bring them back.        
The strategy now is to use new brain scans and other methods to find and
 treat people before they have symptoms of mental decline. 
“The idea is that treatment has to start early to make a difference,” Dr. Watts said.        
Of course, people with the newly discovered mutation have lower levels of beta amyloid for their entire lives. 
“You couldn’t start earlier than that,” Dr. Watts said.