Genetic Assessment Developed to Gauge Risk for Age-Associated Alzheimer’s Disease.

An international team of scientists that includes two School of Public Health researchers has developed a novel genetic score that allows individuals to calculate their age-specific risk of developing Alzheimer’s disease (AD), based upon genetic information.

The study—led by the University of California San Diego School of Medicine and the University of California San Francisco, and published online in PLOS Medicine—uses a polygenic hazard scoring (PHS) system to derive risk assessments for developing AD. The research team combined genetic data from large groups of patients with AD with epidemiological estimates to create the scoring, then replicated the findings in an independent sample and validated them with known biomarkers of Alzheimer’s pathology.

To conduct the study, the researchers analyzed genotype data from more than 70,000 AD patients and normal elderly controls who were participating in several projects, such as the Alzheimer’s Disease Genetics Consortium, the National Alzheimer’s Coordinating Center, and the Alzheimer’s Disease Neuroimaging Initiative. The team scrutinized the data for AD-associated single nucleotide polymorphisms (SNPs), which are variations of a single nucleotide or DNA building block that occur at a specific position in the genome.

There is some SNP variation in genomic information in all humans, which affects individual susceptibility to disease. In this case, the researchers looked at SNPs linked to AD risk and for APOE status. Persons with the E4 variant in the APOE gene are known to be at greater risk of developing late-onset AD.

The researchers developed a continuous polygenic hazard score, or PHS, based on the data to predict age-specific risks of developing AD, then tested it in two independent cohorts. They found persons in the top PHS quartile developed AD at a considerably lower age and had the highest yearly AD incidence rate.

Importantly, PHS also identified people who were cognitively normal at baseline, but eventually developed AD. Even among people who did not have the APOE E4 allele—the most important genetic risk factor for AD—PHS informed age of onset; individuals with high PHS scores developed AD 10 to 15 years earlier than individuals with low PHS.

The authors found that PHS strongly predicted empirical age of AD onset and progression from normal aging to AD, with strongly associated neuropathology and biomarkers of AD neurodegeneration.

The researchers noted several limitations to their study, beyond the need for broader and deeper validation studies. For example, their databases primarily represented individuals of European descent and thus are not indicative of AD incidence and genetic risk in other ethnicities, such as African Americans or Latinos.

The study was led by Rahul Desikan, a clinical instructor in the UCSF Department of Radiology & Biomedical Imaging and a School of Medicine alum. SPH co-authors were Howard Cabral and Adrienne Cupples, professors of biostatistics.