dementia is a group of diseases with symptoms, which affect the way people think and interact with each other. it can often be linked to a disease or damage done to the brain. very often, short-time memory, mind, speech and motor skills are affected. certain forms of dementia cause a change in the personality of the sufferer. a person suffering from dementia will lose certain skills and knowledge they already had. this is the main difference to other conditions affecting the mind. people who suffer from learning problems, or lower intelligence will never acquire certain skills, people suffering from dementia will lose skills they have acquired. dementia is more common in older people, but younger people can be affected as well. certain forms of dementia can be treated, to some extent. the most common form of dementia is alzheimer's disease, which accounts for between 50 and 60 percent of all cases. other types include vascular dementia and lewy body dementia.