US star David Cassidy's announcement that he is suffering from dementia comes as experts predict the condition will take its toll on more people in future.
There are around 850,000 people in the UK with dementia, a ccording to the Alzheimer's Society, and n umbers are expected to rise to more than one million by 2025, as people live longer.
While it mainly strikes in those over 65, there are more than 42,000 people in the UK under that age with dementia.
Symptoms, which get worse over time, include memory loss and difficulties with thinking, problem-solving or language.
Scientists are investigating how dementia might run in the family and how a combination of genes can increase or decrease the risk.
The vast majority of causes of dementia cannot be cured but t here is evidence that a healthy lifestyle can help reduce the risk in middle aged or older people.
Alzheimer's is the most common cause of dementia.
Last year it was announced that Monty Python star Terry Jones had been diagnosed with primary progressive aphasia, a form of dementia.
He recently revealed that he can no longer write.
Other famous sufferers of dementia include the late Baroness Thatcher and Ronald Reagan.
Best-selling author Terry Pratchett died aged 66 in 2015, after a public struggle with Alzheimer's.
Fawlty Towers star Prunella Scales has also been suffering from dementia.
In 2015, Robin Williams's widow said that a coroner's report into the star's death found signs of Lewy body dementia, a difficult-to-diagnose condition which leads to a decline in thinking and reasoning abilities.