Early onset Alzheimer’s. Less than 10% of all Alzheimer’s disease patients have this type This is a rare form of Alzheimer’s disease in which people are diagnosed with the disease before age 65.. Because they experience premature aging, people with Down syndrome are particularly at risk for a form of early onset Alzheimer’s disease. When symptoms first appear adults with Down syndrome are often in their mid- to late 40s or early 50s

More of the brain abnormalities that are associated with Alzheimer’s disease have younger people who develop 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 myoclonus – 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. Accounting for about 90% of cases and usually occurring after age 65. This is the most common form of Alzheimer’s disease,. Late-onset Alzheimer’s disease strikes almost half of all people over the age of 85 and may or may not be hereditary. Late-onset dementia is also called sporadic Alzheimer’s disease.
Familial Alzheimer’s disease (FAD). In affected families, members of at least two generations have had Alzheimer’s disease This is a form of Alzheimer’s disease that is known to be entirely inherited.. 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.