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Dementia is a broad category of brain diseases that cause a long-term and often gradual decrease in the ability to think and remember that is severe enough to affect daily functioning. Other common symptoms include emotional problems, difficulties with language, and a decrease in motivation. Consciousness is usually not affected. A diagnosis of dementia requires a change from a person's usual mental functioning and a greater decline than one would expect due to aging. These diseases have a significant effect on caregivers. The most common type of dementia is Alzheimer's disease, which makes up 50% to 70% of cases. Other common types include vascular dementia, dementia with Lewy bodies, and frontotemporal dementia. Less common causes include normal pressure hydrocephalus, Parkinson's disease dementia, syphilis, HIV, and Creutzfeldt–Jakob disease. More than one type of dementia may exist in the same person. A small proportion of cases run in families.