International researchers said Tuesday they have found a way to assess a person's genetic risk of developing Alzheimer's disease by a given age, a tool that could lead to better diagnosis and treatment.

The report in the journal PLOS Medicine was based on genetic data from more than 70,000 Alzheimer's patients and elderly people without the disease participating in several major global studies on dementia.

Alzheimer's disease is the most common form of dementia, affecting some 47 million people worldwide, and has no cure and no effective treatments.

Most people with the disease begin to show symptoms in their 60s, but rarer cases of early onset Alzheimer's can begin as early as the 30s.

"For any given individual, for a given age and genetic information, we can calculate your 'personalized' annualized risk for developing Alzheimer's disease (AD)," said co-author Rahul Desikan, clinical instructor at the University of California San Francisco Department of Radiology and Biomedical Imaging.

"That is, if you don't already have dementia, what is your yearly risk for AD onset, based on your age and genetic information."

More research is needed before the test can be made available to the public.

Also, researchers noted that their databases mainly included people of European descent, and therefore they could not accurately predict the risk of Alzheimer's in other ethnicities, including African Americans or Latinos.

"This limitation is an unfortunate product of available genetic studies," said co-author Chun Chieh Fan, a doctor in the department of cognitive science at the University of California, San Diego.

"To have good predictive performance, the genetic risk score requires a large amount of data to train, but currently only European cohorts have reached this critical mass."

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