Alzheimer's disease Alzheimer’s disease causes dementia. It is the most common cause of dementia, accounting for about two-thirds of cases in older people. Alzheimer’s disease is a very specific form of dementia and its symptoms include impaired thought, impaired speech, and confusion. Alzheimer’s disease gets worse over time, but the speed of change varies from person to person. The risk that a person with Down syndrome will develop Alzheimer’s disease increases with age at a similar rate as it does in the general population, but 30 to 40 years sooner than is the case for people without Down syndrome. It can be difficult to detect its onset and early course; in people with Down syndrome it may affect their personality first before the more classical early features of memory loss become obviously apparent. It is the person with Down syndrome, their family or carers who will first notice any changes. This should trigger an assessment, initially by the GP and, if necessary, through a referral to a local specialist service. The diagnosis of dementia and specifically of Alzheimer’s disease depends on the following: Evidence of a pattern of change in personality and general functioning that is characteristic of dementia, such as evidence of a deterioration in memory, general mental functioning, living skills, and personality. The exclusion, through a detailed history, clinical examination, and the undertaking of appropriate investigations, of other causes of dementia or of other disorders that might mimic dementia.