A brain disorder has sidelined actor Bruce Willis and drawn attention to a little-known condition that has many possible causes.
The Hollywood actor's family released a statement on Wednesday announcing he would be stepping away from his acting career as a result of the condition.
For an actor, aphasia could pose a huge challenge depending on how severe it is, experts say.
Biomedical Scientist Zac Turner says the condition is common in older people. Willis is 67.
What is aphasia?
Johns Hopkins University cognitive scientist Brenda Rapp, who works with people with the condition, says the disorder leads to problems with speaking, reading and writing.
"You can imagine how frustrating it is if you can't find words, if you can't organise words into sentences, if you can't get your mouth to produce the sounds you want it to produce," Dr Rapp says.
Aphasia impacts a person's language skills, not the ideas and thoughts behind them.
What causes the brain disorder?
Dr Turner says there are several causes of aphasia.
"You have different sorts of trauma whether it's an infection or head injuries, this is a big thing that's happening in the US and Australia about wearing headgear and the amount of concussions that people have," Dr Turner said.
"Brain tumour, migraines and seizures can also cause it."
For most people, the cause is a stroke that has cut off blood to part of the brain.
How is it impacting Bruce Willis?
Willis' family say the condition is "impacting his cognitive abilities".
They did not comment further on how long he has been experiencing health issues or what caused the diagnosis.
Dr Rapp says it could be "very disruptive for Bruce Willis himself in terms of communicating with others and not being able to find the words to express himself."
What treatment is available?
Some people improve dramatically in a few months, others may need to find other ways to communicate.
Dr Rapp says speech and language therapy can help.
Researchers are looking into new types of speech therapy and non-invasive methods such as a procedure that uses magnetic pulses to stimulate brain cells.
ABC/wires
