Alzheimer's disease is a progressive condition caused by protein ‘plaques’ and ‘tangles’ that lead to the death of brain cells. People in the early stages of Alzheimer's disease often experience problems with their memory and finding the right words. They can then become confused, experience mood swings and feel angry or frustrated as their challenges increase.
Alzheimer's disease is the most common form of dementia in younger people, accounting for around a third of young people with dementia. Some people who are affected will have a family history of young onset dementia in their family. People with Down's syndrome and other learning disabilities can also develop dementia at an early age. When people with Down's syndrome develop dementia, this is usually due to Alzheimer's disease.
You will find more detailed information from Alzheimer's Research UK about the condition here.
If you are affected by Familial Alzheimer's disease, you may find this informaation from Rare Dementia Support helpful.