Alzheimer’s disease: types of Alzheimer’s disease

There are three known types of Alzheimer’s disease. Doctors have categorised Alzheimer’s into the following types:

• Early-onset Alzheimer’s. This is a rare form of Alzheimer’s disease in which people are diagnosed with the disease before the age of 65. Less than 10% of all Alzheimer’s disease patients have this type. Because they experience premature ageing, people with Down’s syndrome are particularly at risk for a form of early onset Alzheimer’s disease. Adults with Down’s syndrome are often in their mid- to late 40s or early 50s when symptoms first appear. Younger people who develop Alzheimer’s disease have more of the brain abnormalities that are associated with Alzheimer’s disease. Early-onset Alzheimer’s appears to be linked with a genetic defect on chromosome 14, to which late-onset Alzheimer’s is not linked. A condition called myoclonic seizure disorder - a form of muscle twitching and spasm - is also more commonly seen in early-onset Alzheimer’s than in late-onset Alzheimer’s.
• Late-onset Alzheimer’s. This is the most common form of Alzheimer’s disease, accounting for about 90% of cases and usually occurring after age 65. Late-onset Alzheimer’s disease strikes almost half of all people over the age of 85 and hereditary factors may be important in some cases. Late-onset dementia is also called sporadic Alzheimer’s disease.
• Familial Alzheimer’s disease (FAD). This is a form of Alzheimer’s disease that is known to be entirely inherited. In affected families, members of at least two generations have had Alzheimer’s disease. FAD is extremely rare, accounting for less than 1% of all cases of Alzheimer’s disease. It has a much earlier onset (often in the 40s) and can be clearly seen to run in families.