Bruce Willis suffering from frontotemporal dementia

Nearly a year after Bruce Willis' family announced that he would step away from acting after being diagnosed with aphasia, his family says his "condition has progressed."

In a statement posted Thursday, the 67-year-old actor's family said Willis has a more specific diagnosis of frontotemporal dementia.

"While this is painful, it is a relief to finally have a clear diagnosis," the statement read. "FTD is a cruel disease that many of us have never heard of and can strike anyone."

Last March, Willis' family said his aphasia had affected his cognitive abilities. The condition causes loss of the ability to understand or express speech.

In Thursday's statement, his family said communication challenges were just one symptom of frontotemporal dementia.

The Association for Frontotemporal Degeneration describes FTD as a group of brain disorders caused by degeneration of the frontal and/or temporal lobes of the brain that affects behavior, language and movement. Aphasia can be a symptom of it. The association describes frontotemporal degeneration as "an inevitable decline in functioning," with an average life expectancy of seven to 13 years after the onset of symptoms.

"Today there are no treatments for the disease, a reality that we hope can change in the years ahead," the family's statement read, adding that it can take years to get a proper diagnosis. "As Bruce's condition advances, we hope that any media attention can be focused on shining a light on this disease that needs far more awareness and research."

The statement was posted on the website for the Association for Frontotemporal Degeneration and signed by Willis' wife, Emma Heming Willis, his ex-wife Demi Moore, and his five children, Rumer, Scout, Tallulah, Mabel and Evelyn.

Over a four-decade career, Willis' movies had earned more than $5 billion at the worldwide box office. While beloved for hits like "Die Hard" and "The Sixth Sense," the prolific actor had in recent years primarily featured in direct-to-video thrillers.

"Bruce has always found joy in life — and has helped everyone he knows to do the same," the family said Thursday. "It has meant the world to see that sense of care echoed back to him and to all of us. We have been so moved by the love you have all shared for our dear husband, father, and friend during this difficult time. Your continued compassion, understanding, and respect will enable us to help Bruce live as full a life as possible."