The most common, accounts for at least 60 per cent of all cases. No single known cause, but genetic mutations and other factors (such as head trauma) greatly increase risk. Difficulty remembering names and recent events is common; apathy and depression also among early symptoms. Later indicators include impaired judgment, disorientation, confusion, behaviour change and difficulty speaking, swallowing and walking. Hallmark: abnormal deposits in brain of a protein fragment, beta-amyoloid (plaques), and twisted strands of the protein tau (tangles).
The second most common, accounts for about 20 per cent of cases. Symptoms similar to those of Alzheimer's, although memory may not be affected as seriously. Brain damage caused by decreased cranial blood flow, often due to transient ischemic attacks (TIAs), or mini-strokes.
Caused by damage to brain cells, especially in front and side regions of the brain, and features marked changes in personality and behaviour, as well as difficulty with language. No common abnormality, but one type, called Pick's bodies, features tau proteins that aggregate in silver spherical forms.
Lewy bodies dementia
The pattern of decline is similar to Alzheimer's, including problems with memory and judgment and behaviour changes, but visual hallucinations, muscle rigidity and tremors are also common. Hallmark: abnormal deposits of a protein, alpha-synuclein, in brain's nerve cells.