By Janet Fang
Posting in Science
A chronology of subtle changes to the brain shows how signs of Alzheimer's are detectable 25 years before symptoms like memory loss develop. Also, a genetic mutation that defends against the disease.
Treatments for Alzheimer's have been unsuccessful, in part because people received drugs only after symptoms had become obvious, and their brains were too damaged to recover.
By constructing a detailed chronology of molecular changes to the brain and spinal fluid of Alzheimer's patients, scientists show that the first detectable signs occur 25 years before memory loss. Technology Review reports.
That's sooner than MRI exams, blood analyses, and other tests -- offering early hints that a drug works. With a roadmap of the disease's signature, doctors will have a better chance of judging whether a treatment is working rather than waiting until the disease is full-blown, says study author Randall Bateman at Washington University.
The timeline was constructed from studies of 128 people from families with a rare, inherited form of Alzheimer's where symptoms emerge in patients still in their 30s.
- Levels in the spinal fluid of AB42, a protein associated with Alzheimer's, begins to decline 25 years before the onset of symptoms.
- At 15 years before symptoms develop, levels of another protein, called tau, begin to rise, and some brain shrinkage and atrophy is evident.
- At 10 years out, the brain's consumption of the sugar glucose is discernibly lower, and some memory impairment can be measured.
The team measured key molecules in healthy volunteers (but whose genes predict they'll develop Alzheimer's). By learning at what age those volunteers' parents first developed symptoms, the researchers were able to infer the time span between the molecular changes and the disease's onset.
Family members who didn't inherit the Alzheimer's genes showed none of these early signs of the disease, Bateman says, suggesting that the markers do distinguish between people with early-stage disease and those without.
The research was published in the New England Journal of Medicine this week.
Also this week, scientists show that a lucky few people carry a genetic mutation that naturally prevents them from developing the condition: about 0.5% of Icelanders are carriers, as are 0.2-0.5% of Finns, Swedes, and Norwegians. Compared with their countrymen who lack the mutation, they are more than 5 times more likely to reach 85 without being diagnosed with Alzheimer's.
Images: Bateman et al.
Jul 13, 2012