Kimberly Williams-Paisley is opening up about her mother’s struggle with dementia. Experts say there are important signals to watch out for if you’re concerned about a loved one.

Kimberly Williams-Paisley is coming forward about her mother’s struggle with dementia. In an interview with the Today show, Williams-Paisley said she and her husband Brad Paisley first noticed something was wrong with her mother when she wasn’t able to read a passage at their 2003 wedding.

The Father of the Bride star shared a video of her mother, Linda Williams, trying to read the passage and said they noticed something was wrong because she was “acting very irrationally” and was “very emotional.”

“[She] really wanted to be involved in the ceremony at the last minute,” Williams-Paisley said. “So, we gave her something to read, and she stood up in front of the congregation and wasn’t able to get through the reading, which was very atypical of my mom.”

Williams was later diagnosed with a rare form of early-onset dementia called primary progressive aphasia. Williams-Paisley details the path to her mother’s diagnosis and how her family has coped with it in her new book Where the Light Gets In: Losing My Mother Only to Find Her Again.

Williams-Paisley’s family’s struggle isn’t rare. According to the Centers for Disease Control and Prevention (CDC), as many as 5 million Americans were living with Alzheimer’s disease (the most common form of dementia) in 2013, the most recent year for which data is available. By 2050, that number is expected to rise to 14 million.

The CDC calls dementia an “umbrella term” for a group of cognitive disorders that are usually characterized by memory impairment, and difficulty with language, motor activity, object recognition, and the ability to plan and organize, noting that it’s considered an illness of “older adults.”

So, what are the early signs of dementia to look out for in a loved one?

Bradford Dickerson, M.D., an associate professor of neurology at Harvard Medical School and co-director of the Neuroimaging Group, Gerontology Research Unit at Massachusetts General Hospital, tells SELF that one of the biggest tip-offs is when someone has trouble doing something they’ve done for years. Like Williams, “it can start out with difficulties, like a person has a public speaking or similar engagement and they can’t collect their thoughts in a way that’s characteristic for them,” he says. “These difficulties are new and are affecting a person in a way that is not consistent with something they’ve dealt with for many years.”

Clifford Segil, D.O., a neurologist at California’s Providence Saint John’s Health Center, tells SELF that symptoms can vary depending on the type of dementia a person has. Aphasia, which Williams has, is a rare form in which people lose the ability to express themselves, he says.

But Alzheimer’s dementia is the most common, he says. Early signs include the inability to remember more recent events (but a person can remember old events). “They can tell you what they were wearing at their wedding but they can’t remember what they had for breakfast,” Segil says. “People may also ask you to repeat things, they may repeat things, and may ask things like ‘Where did we go for dinner again last night? Who was there?’ Those are the earliest signs.”

The second most common form of progressive dementia is Lewy body dementia (which Robin Williams suffered from), a form that causes a progressive decline in mental abilities. With Lewy body dementia “People are shaky and start acting strangely,” Segil says.

The final most common form is vascular dementia, in which people can have an “acute change out of the blue,” Segil says. A person’s temperament may change all of the sudden, stay the same for a while, and then change again. “People often describe it as a patient is suddenly ‘different,’” Segil says.

Dickerson admits that it can be challenging to separate what might be the effects of normal aging and early signs of dementia, but says it’s a good idea to get a loved one evaluated if you have concerns they’re in cognitive decline. Since people who suffer from early-onset dementia may have difficulty with details that are important for their evaluation, Dickerson recommends escorting a loved one to their primary care physician and expressing your concerns. That doctor may then order additional testing or send your loved one to a specialist for more evaluation.

If you feel that your loved one’s primary care physician isn’t taking your concerns seriously enough, experts recommend going to a dementia specialist. There are other conditions that can cause dementia-like symptoms, like a stroke or hypothyroidism, Dickerson points out, and it’s a good idea to rule those out first.

If you have concerns, don’t wait—it could affect your loved one’s treatment. Segil stresses the importance of early detection in treating dementia: “There’s no medications that will make things better, but there are medications that can slow things down.”