Actor and singer David Cassidy, 66, revealed this week to People that he is suffering from dementia. His diagnosis comes after he watched his mother “disappear” into the disease until she died at age 89, and after his grandfather struggled with it as well. “I was in denial, but a part of me always knew this was coming," Cassidy said in an interview.

Dementia is a broad term that can refer to many different types of cognitive problems and memory loss, and Cassidy does not specify which type of dementia he has been diagnosed with. But several—including Alzheimer’s disease, the most common type—do tend to run in families.

“You can get dementia from a head injury, a stroke, or an infection in your brain, and these things are usually not going to be genetic,” says Douglas Scharre, MD, director of the Division of Cognitive Neurology at The Ohio State University Wexner Medical Center. “But most of the degenerative dementias, the kind that occurs over time with age, are very often related to certain genes.” (Dr. Scharre has not treated Cassidy.)

That doesn’t mean, however, that everyone whose mother or father has Alzheimer’s disease will inevitably develop it too. “We think it’s more polygenic—that is, multiple genes might help increase your risk, rather than just one,” says Dr. Scharre. Children can inherit these genes, he says, but it’s rare that parents pass on a 100% chance of developing dementia.

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“You’re definitely at increased risk, but you can have a family history of Alzheimer’s and never get it yourself,” says Dr. Scharre. “And there are lots of cases in which there’s no family history, and it doesn’t seem to be related to genetics at all.”

When dementia is influenced by genetics, people tend to develop it in the same decade their parents did. Although he doesn’t know the details of Cassidy’s diagnosis or family history, Dr. Scharre says the actor’s relatively young age does suggest a genetic component.

Only about 3% of people between ages 65 and 74 have dementia, according to a 2016 study in JAMA Internal Medicine. For Alzheimer’s disease, people diagnosed under age 65 are considered to have an “early onset.”  

Early signs of dementia can include mood changes and trouble forming new short-term memories. While a person may remember stories that happened years ago, they may forget—and repeatedly ask about—details they just learned an hour ago. Misplacing items more frequently, and forgetting the names of household objects, can be symptoms as well.

Sense of direction can also be affected early on. “If you’re getting turned around in a place that should be familiar to you, that could be an early sign of dementia,” says Dr. Scharre.

While performing over the weekend, Cassidy struggled to remember lyrics to songs he had been singing for nearly 50 years. This could suggest a loss of older memories—a sign that Cassidy’s dementia has progressed past the early stage, says Dr. Scharre. But it’s also possible that the singer simply “lost his train of thought and forgot where he was in the song,” he adds.

Dr. Scharre recommends that people with a family history of dementia take a baseline cognitive test before they reach the age their mother or father developed the disease. Screenings can be conducted in a doctor’s office, or with an at-home screening tool Dr. Scharre developed, called the Self-Administered Gerocognitive Exam (SAGE).

“If your mom had symptoms in her 70s, get an evaluation before you turn 70 and then get retested every couple of years” he says. “That way you and your doctor can tell if you start to decline.” That’s worth knowing, he says, because current drugs for dementia work best when started early. Most degenerative types of dementia can’t be reversed, but medications may be able to slow their progression.

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People in the early stages of dementia may be able to enroll in clinical trials, as well, to gain access to experimental new treatments. “Even if it ends up being too late to help the patients themselves, it could help their children,” says Dr. Scharre.

And whether you have a family history or not, Dr. Scharre recommends staying fit, getting regular exercise, and keeping your mind busy with activities like reading, puzzles, and social engagements. “People who are very active, mentally and physically, seem to have a slower course in general,” he says.

“I’m a firm believer in ‘use it or lose it,’” he continues. “Using your brain is going to help build up those synapses, build up those connections, so that if a terrible disease starts killing those nerve cells, you have more of a reserve.”