Around 12% of young people with dementia have frontotemporal dementia or FTD (including the condition formerly known as Pick’s disease). It most commonly occurs between the ages of 45-65.
Familial frontotemporal dementia (fFTD) is an inherited form of the conditioin and occurs in about 40% of cases of FTD.
As the name suggests, frontotemporal dementia is caused by damage to the cells in the frontal and temporal lobes of the brain. The frontal lobe controls our emotions, behaviour and personality. The temporal lobes are responsible for language.
Several different conditions can affect these lobes and 'frontotemporal dementia' is the broad term to describe them all. Symptoms vary depending on the exact areas of the brain affected but people can become aggressive, obsessive and lose their inhibitions. Other people will struggle with speech.
Subtypes of frontotemporal dementia are identified clinically according to the symptoms that appear first and most prominently. Clinical diagnoses include behavioural variant (bvFTD), PPA and the movement disorders PSP and corticobasal degeneration (CBD).
You may find the information in this Alzheimer's Society publication about FTD useful.