A person’s chance of developing dementia is influenced by family history, variations in certain genes, and medical conditions such as cardiovascular disease and diabetes. But less is known about the factors that affect when the first symptoms of forgetfulness and confusion will arise.
A new study from Washington University School of Medicine in St. Louis reveals that people with dementia – whose parents also had dementia – develop symptoms an average of six years earlier than their parents. Factors such as education, blood pressure and carrying the genetic variant APOE4, which increases the risk of dementia, accounted for less than a third of the variation in the age at onset – meaning that more than two-thirds remains to be explained.
“It’s important to know who is going to get dementia, but it’s also important to know when symptoms will develop,” said first author Gregory Day, MD, an assistant professor of neurology and an investigator at the Charles F. and Joanne Knight Alzheimer’s Disease Research Center (ADRC). “If we can better understand the factors that delay or accelerate the age at onset, we eventually could get to the point where we collect this information at a doctor’s visit, put it through our calculator, and determine an expected age at onset for any adult child of a person with dementia.”
The study is available online in JAMA Network Open.
Alzheimer’s disease is the most common cause of dementia, affecting an estimated 5.8 million people in the United States. Between 10% and 15% of the children of Alzheimer’s patients go on to develop symptoms of the disease themselves.
Day and colleagues, including senior author John C. Morris, MD, the Harvey A. and Dorismae Hacker Friedman Distinguished Professor of Neurology and head of the Knight ADRC, studied people with dementia who were participating in research studies at the Knight ADRC. They identified 164 people with dementia who had at least one parent who had been diagnosed with dementia.
Using medical records and interviews with participants and knowledgeable friends or family members, the researchers determined the age at onset of dementia for each participant and his or her parent or parents. People with one parent with dementia developed symptoms an average of 6.1 years earlier than the parent had. If both parents had dementia, the age at onset was 13 years earlier than the average of the parents’ ages at diagnosis.