FTD is the most common cause of dementia in people under the age of 60.
Willis announced that there is frontotemporal dementia. A form of dementia known as FTD is a reduced number of nerve cells in the frontal and temporal lobes of the brain.
FTD is a cruel disease people have never heard of and can happen to anyone, the family wrote in a statement.
There are two main variants of FTD. Primary progressive aphasia impairs the patient's competence. Frontotemporal dementia manifests as personality and behavior.
Most of all it hits the parts of the brain that make us most human, said Dr Bruce Miller, professor of neurology at the University of California, San Francisco.
Susan Dickinson, chief executive of the Association for Frontotemporal Degeneration, said FTD was the most common cause of dementia in people under the age of 60.