Newswise, July 8, 2016 – New research shows that a genetic
risk score may detect those at higher risk for Alzheimer’s disease long before
symptoms appear—even possibly in healthy young adults, according to a study
published in the July 6, 2016, online issue of Neurology®, the medical journal
of the American Academy of Neurology.
“The stage of Alzheimer’s before symptoms show up is thought
to last over a decade,” said Elizabeth C. Mormino, PhD, with Massachusetts
General Hospital in Charlestown, Mass.
“Given that current clinical trials are testing whether
therapies can slow memory and thinking decline among people at risk for the
disease, it is critical to understand the influence of risk factors before
symptoms are present.”
For the study, researchers calculated a polygenic risk score,
or a numeric score based on whether or not a person has several high-risk gene
variants, in 166 people with dementia and 1,026 without dementia.
Participants had an average age of 75. Scientists also looked
for specific markers of Alzheimer’s disease. The markers included memory and
thinking decline, clinical progression of the disease and the volume of the
hippocampus (the memory center of the brain).
Researchers also looked at links between the risk score and hippocampus volume in 1,322 healthy, younger participants between the ages of 18 and 35.
The study found that within older people free of dementia, a
higher polygenic risk score was associated with worse memory and smaller
hippocampus at the start of the study, accounting for 2.3 percent of the total
variance in memory and 2.0 percent of the variance in hippocampus volume.
Over the three years of the study, a higher score was also
linked to greater longitudinal memory and executive function decline and
clinical progression of the disease.
Finally, the risk score was associated with overall disease
progression, with 15 of 194 participants that were cognitively normal at the
start of the study developing mild cognitive impairment or Alzheimer’s disease,
and 143 of 332 with mild cognitive impairment at the start of the study
developing Alzheimer’s disease after three years. Each standard deviation
increase in polygenic risk was associated with a 1.6 times increase in risk of
clinical progression.
Within the younger group, a higher risk score was tied to
smaller hippocampus volume. For the younger group, the risk score accounted for
0.2 percent of the difference in hippocampus volume between those with high and
low risk scores.
“Our study was small and larger numbers of participants will
need to be studied to confirm our findings,” said Mormino. “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.”
The study was supported by the National Institutes of Health.
To learn more about Alzheimer’s disease, please visit http://www.aan.com/patients.
The American Academy of Neurology, the world’s largest
association of 30,000 neurologists and neuroscience professionals, is dedicated
to promoting the highest quality patient-centered neurologic care. A
neurologist is a doctor with specialized training in diagnosing, treating and
managing disorders of the brain and nervous system such as Alzheimer’s disease,
stroke, migraine, multiple sclerosis, brain injury, Parkinson’s disease and
epilepsy.
For more information about the American Academy of Neurology,
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