The most common type of dementia, it accounts for at least 60 per cent of cases. There is no single known cause, but there are some genetic mutations that greatly increase risk and some factors (like head trauma) that also increase risk.
Symptoms Difficulty remembering names and recent events is a common clinical symptom; apathy and depression are also early symptoms. Later symptoms include impaired judgment, disorientation, confusion, behaviour change and difficulty speaking, swallowing and walking.
Hallmarks The hallmark of Alzheimer's is abnormal deposits in the brain of the protein fragment beta-amyloid (plaques) and twisted strands of the protein tau (tangles).
The second most common cause of dementia, it accounts for about 20 per cent of causes.
Symptoms They are similar to those of Alzheimer's, although memory loss may not be as seriously affected.
Hallmarks Brain damage is caused by decreased blood flow to parts of the brain, often due to transient ischemic attacks (TIAs), or mini-strokes.
Refers to dementia caused by damage to brain cells, especially in the front and side regions of the brain
Symptoms Typical symptoms involve marked changes in personality and behaviour, as well as difficulty with language.
Hallmarks There is no common abnormality in the brain of all cases, but one type, Pick's bodies, is characterized by tau proteins that aggregate in silver spherical forms.
Lewy Bodies Dementia
Symptoms 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.
Hallmarks The hallmark of the disease is abnormal deposits in the nerve cell of the brain of the protein alpha-synuclein.
A brain disorder that impairs memory and co-ordination and causes severe behaviour changes, it is also rapidly fatal.
Symptoms Can occur spontaneously, but the new variant form of CJD is caused by the consumption of products from cattle with mad cow disease.
Hallmarks The hallmark of the disease is misfolded prion protein in the brain.
Symptoms Most people with Parkison's (a disorder that involves movement problems) also develop dementia in the later stages of the disease.
Hallmarks The hallmark of the disease is Lewy bodies inside the nerve cells of the brain.
Normal Pressure Hydrocephalus
This is the formal term given to the build-up of fluid in the brain, sometimes colloquially called "water on the brain."
Symptoms They include difficulty walking, memory loss and incontinence.
Hallmarks This form of dementia is sometimes reversible with the installation of a shunt in the brain to drain excess fluid.
Delirium is used to describe a sudden state of confusion and disorientation. It is almost always caused by a medical problem, such as a drug reaction, an infection, a heart problem or a stroke. Delirium is not a dementia per se, but often occurs in people with dementia.