Pat Summitt, the legendary University of Tennessee women's basketball coach who died today at the age of 64, was diagnosed with early-onset dementia five years before her death.

In a statement, her son Tyler said she died peacefully, after putting up a fierce fight against the disease.

"Since 2011, my mother has battled her toughest opponent, early onset dementia, 'Alzheimer's Type,' and she did so with bravely fierce determination just as she did with every opponent she ever faced," he said. "Even though it's incredibly difficult to come to terms that she is no longer with us, we can all find peace in knowing she no longer carries the heavy burden of this disease."

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Summit was just 59 years old when she was first diagnosed with early onset dementia, Alzheimer's type, in 2011. Early-onset, also known as younger-onset, refers to cases diagnosed in people younger than 65.

According to the Alzheimer's Association, up to 5 percent of the more than 5 million Americans with Alzheimer's disease have early-onset.

What are the symptoms?

For many people with early-onset Alzheimer's, symptoms are similar to those of other forms of the disease, which becomes more common in older age.

Early symptoms include forgetting newly learned information and important dates; difficulty solving basic problems like keeping track of bills or following recipes; losing track of the date or time of year; misplacing things; and not being able to retrace your steps.

As the disease progresses, symptoms may also include severe mood swings and behavioral changes; suspicions about friends, family members and caregivers; difficulty speaking; and severe memory loss.

However, in some cases, early-onset Alzheimer's can present differently than other forms of the disease.

"Early-onset Alzheimer's is a little bit different from regular Alzheimer's in that you can have somewhat more varied presentation," Dr. Thomas Wisniewski, director of the Center for Cognitive Neurology at NYU Langone Medical Center, told CBS News.

Some of these symptoms have nothing to do with memory. "They can present with executive dysfunction," Wisniewski said, meaning the person may have trouble with reasoning and problem-solving skills. "Problems with speech, and visual disturbances like difficulty interpreting spatial relationships or controlling their gaze" can also become apparent.

Who's at risk for early-onset Alzheimer's?

Scientists are not exactly sure what causes early-onset Alzheimer's disease, but research shows there is a strong genetic component.

"Genetics plays a greater role than in late-onset Alzheimer's," Wisniewski said. "In particular there have been three genes identified -- presenilin 1, amyloid precursor protein, and presenilin 2, in order of importance -- that can have mutations that are associated with early-onset Alzheimer's."

Yet, he notes that those three genes only account for around 10 percent of early-onset cases. "In the majority of early-onset cases, we don't know what the cause is," he said.

Does the disease progress faster when it's early-onset?

Early-onset cases of Alzheimer's often progress more quickly than other forms. "The pathology tends to be more extreme in early-onset," Wisniewski said. "Many can deteriorate more quickly, so it is a more aggressive disease."

That's because the genetic mutations than can cause early-onset Alzheimer's lead to a greater production of amyloid-beta, the protein fragments that build up into plaques and are associated with Alzheimer's disease.

"When you look at the pathology, it is just like late-onset Alzheimer's disease but there's just more of it," Wisniewski said.

He also points out that each individual is different and some early-onset cases can last a very long time, depending on supportive care.

How close are we close to a cure?

Currently, patients with early-onset Alzheimer's disease have a few FDA-approved drug treatments to choose from that may help reduce symptoms. However, they will not cure the disease or stop it in the long run.

Keeping physically fit and mentally active can also help stave off the disease's progression with both early and late-onset cases, Wisniewski said.

Another option is to become a participant in a clinical trial, where scientists are testing potential new treatments and therapies aimed at more directly addressing the underlying pathology of the disease, as opposed to merely treating the symptoms.

When asked how close he thinks science is to finding a cure, Wisniewski said things are looking much more hopeful, though we still have a ways to go.

"It's clear that Alzheimer's is a syndrome, so it has a number of different causes and the optimum treatment may be dependent on what the underlying cause of the particular form of Alzheimer's disease," he said. "With the greater spectrum of different approaches to treatment being tried, I think that increases the probability of finding approaches that will be more efficacious in at least a subset of cases."