Bruce Willis diagnosed with frontotemporal dementia. It's a 'cruel disease' and the most common form of dementia in people under 60.

• Bruce Willis has been diagnosed with frontotemporal dementia, his family announced.
• The action movie superstar stepped away from acting last year after being diagnosed with aphasia.

Nearly a year after Bruce Willis announced he'd be stepping away from acting following an aphasia diagnosis, the action superstar's family announced Thursday that he has been diagnosed with frontotemporal dementia.

"Bruce's condition has progressed and we now have a more specific diagnosis: frontotemporal dementia (known as FTD). Unfortunately, challenges with communication are just one symptom of the disease Bruce faces," the family's statement, posted on The Association for Frontotemporal Degeneration's website, said.

The "cruel disease" can "strike anyone," the family said, adding that "for people under 60, FTD is the most common form of dementia, and because getting the diagnosis can take years, FTD is likely much more prevalent than we know."

There are no current treatments for the disease, according to The Association for Frontotemporal Degeneration.

The condition can cause changes to behavior and personality as well as problems with language

Frontotemporal dementia refers to a group of disorders that affect areas of the brain behind the forehead (the frontal lobe) and behind the ears (temporal lobes), according to the Mayo Clinic. It occurs at a younger age than other types of dementia, often between ages 40 and 60, and is the most common form of dementia among people under 60.

It occurs when nerve cell damage begins to cause problems in those parts of the brain, which regulate language, behavior, and personality. Symptoms can vary, according to the Mayo Clinic. For instance, a person may struggle to understand words, could start to act out impulsively, or have extreme changes in personality. Patients may also have a lack of interest in normal activity, which is sometimes misdiagnosed as depression.

Frontotemporal dementia can have similar signs as Alzheimer's, including memory loss, according to the Alzheimer's Association. However, there are key differences. Behavior changes can be an early warning sign of frontotemporal dementia, but doesn't show up in Alzheimer's patients until later stages of the disease.

The condition is degenerative, and while some symptoms can be managed with medication and other types of care, it increases the risk of illness, injury, and infection, according to the Association for Frontotemporal Degeneration.

The Willis family vows to bring attention to this condition

Bruce Willis' family statement thanked the "outpouring of love and compassion for Bruce over the past ten months."

"Your generosity of spirit has been overwhelming, and we are tremendously grateful for it. For your kindness, and because we know you love Bruce as much as we do, we wanted to give you an update," the Willis family said.

"Bruce has always found joy in life – and has helped everyone he knows to do the same. It has meant the world to see that sense of care echoed back to him and to all of us," the statement, signed Emma, Demi, Rumer, Scout, Tallulah, Mabel, and Evelyn, said.

It added: "Bruce always believed in using his voice in the world to help others, and to raise awareness about important issues both publicly and privately. We know in our hearts that – if he could today — he would want to respond by bringing global attention and a connectedness with those who are also dealing with this debilitating disease and how it impacts so many individuals and their families."