The term 'dementia' is used to describe the symptoms that occur when the brain is affected by specific diseases and conditions.
Symptoms of dementia include loss of memory, confusion and problems with speech and understanding.
Dementia is progressive, which means the symptoms will gradually get worse.
For more information about dementia visit the Alzheimer's society website.
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The letter was signed by the CBI, British Chambers of Commerce, the EEF, the Institute of Directors and the Federation of Small Businesses.
A spokesperson said Rory Stewart's remarks were in line with the British government’s stated position.