Frontotemporal dementia - Causes of frontotemporal dementia

Frontotemporal dementia is caused by a build-up of abnormal proteins affecting the frontal and temporal areas of the brain (behind the forehead and above and behind the ears).

The abnormal proteins clump together and become toxic to the brain cells, causing them to die. The frontal and temporal lobes are most affected and shrink over time.

It's not yet fully understood why these abnormal proteins build up, but there is often a strong genetic cause. About a third to a half of cases of frontotemporal dementia are inherited and run in families.

Mutations (alterations) in three genes account for the majority of these inherited cases:

• the tau gene
• the progranulin gene 
• a recently discovered gene called C9orf72 that can cause motor neurone disease or frontotemporal dementia

Tau protein is involved in some cases of frontotemporal dementia. This protein is present in all nerve cells and has an important role in transporting other essential proteins between nerve cells in the brain.

A mutation in the gene that codes for tau protein causes abnormal tau to build up. This particular mutation is found on chromosome 17 (see the box, top right, for an explanation of genes and chromosomes).

Without a usable form of tau protein, and with an abnormal form of the protein building up, the brain cells cannot function properly and so they die.

Other types of frontotemporal dementia will be associated with different genes, proteins and chromosomes. In other words, there is no single common cause of frontotemporal dementia.