It’s estimated that 5.5 million U.S. adults are now living with Alzheimer’s disease.
The large majority of these people (5.3 million) are over the age of 65.
The costs of caring for people with Alzheimer’s are also significant. Almost $260 billion in healthcare costs are predicted for this year.
The medical research community is working to find ways of diagnosing Alzheimer’s as early as possible. In the near future, physicians hope to be able to treat the disease before irreversible damage occurs.
A team of international researchers, led by scientists at University of California-San Diego (UCSD) School of Medicine and University of California-San Francisco (UCSF), are moving closer to this goal.
The team designed a genetic score that they say predicts the risk of dementia among aging individuals with a high degree of accuracy.
The findings were published in the journal PLOS Medicine.
Analyzing genetic variations
Researchers analyzed the genotype of more than 70,000 patients with Alzheimer’s enrolled in several studies.
They collected genetic data from healthy individuals in a control group.
The scientists focused on single nucleotide polymorphisms (SNPs) that are commonly associated with Alzheimer’s.
SNPs are the most widespread type of genetic variation in our DNA. These variations are sometimes associated with certain illnesses, so they serve as biomarkers that help scientists to identify the disease.
In this study, the scientists examined Alzheimer’s-related SNPs as well as the status of the APOE gene. The APOE gene is responsible for encoding apolipoprotein E - a protein that ultimately forms lipoproteins, which enclose and carry cholesterol and other fats through the bloodstream.
People that have the E4 variation of the APOE gene are known to be more likely to develop age-induced Alzheimer’s.
Based on this information and the data collected, the researchers used a polygenic score to determine the risk of developing age-related Alzheimer’s. They then tested it on two separate samples of people.
A polygenic hazard score (PHS) is the weighted sum of gene variation used to predict individual genetic traits and assess disease risk.
Study co-first author Rahul S. Desikan, Ph.D., clinical instructor in the UCSF Department of Radiology and Biomedical Imaging, explained the study procedure.
“We combined genetic data from large, independent cohorts of patients with AD with epidemiological estimates to create the scoring, then replicated our findings on an independent sample and validated them with known biomarkers of Alzheimer’s pathology,” Desikan said.
Accurate genetic tool
The researchers found that people scoring in the top 25 percent of the PHS developed Alzheimer’s at a much younger age and had the highest incidence.
Those with a high PHS score developed Alzheimer’s 10 to 15 years earlier than those with a low PHS.
Using the PHS score, the scientists were also able to identify the people who ultimately developed Alzheimer’s, despite the fact that they were cognitively healthy at the start of the study.
The tool enabled researchers to identify the age of Alzheimer’s (AD) onset even among participants who did not have the APOE E4 gene variation. The calculated score correlated strongly with neuropathology and AD-specific neurodegeneration.
“For any given individual, for a given age and genetic information, we can calculate your ‘personalized’ annualized risk for developing AD. That is, if you do not already have dementia, what is your yearly risk for AD onset, based on your age and genetic information. We think these measures of polygenetic risk, of involving multiple genes, will be very informative for early AD diagnosis, both in determining prognosis and as an enrichment strategy in clinical trials,” said Deskian.
The study’s senior author also commented on the significance of the findings.
“From a clinical perspective, the polygenic hazard score provides a novel way not just to assess an individual’s lifetime risk of developing AD, but also to predict the age of disease onset,” said Anders Dale, Ph.D., who is also a professor in neurosciences, radiology, psychiatry, and cognitive science at the University of California-San Diego School of Medicine.
“Equally important, continuous polygenic testing of AD genetic risk can better inform prevention and therapeutic trials and be useful in determining which individuals are most likely to respond to therapy,” Dale added.
The authors also point out some of the study’s limitations.
For instance, the genetic data they used mainly belonged to people of European descent, so the study offers no evidence as to how PHS works for people of other ethnicities.