We don’t know exactly what causes FTD. Experts think that the disease is due to a mixture of genetic, medical and lifestyle factors. Even allowing for its under-recognition in older people, FTD does not show the very strong link with ageing seen for more common dementias such as Alzheimer’s disease or vascular dementia.
Autopsy studies show that the death of nerve cells in the frontal and temporal lobes is linked to clumps of abnormal proteins inside the cells, including proteins called tau and TDP-43. The tau protein may take the form of Pick bodies, which gave FTD its original name of Pick’s disease – after Dr Arnold Pick who first studied the dementia.
Frontotemporal dementia is much more likely to run in families than the more common forms of dementia are. About one third of people with the condition have some family history of dementia. About 10–15 per cent of people with FTD have a very strong family history of the condition, with several close relatives in different generations affected. This pattern is most common in the behavioural type of FTD and least common in semantic dementia.
Typically in these cases, FTD is inherited from a parent as a defect (mutation) in one of three genes: MAPT, GRN or C9ORF72.
Each of the children or siblings of someone with a mutation that is known to cause FTD has a 50 per cent chance of carrying the same mutation. Families with a known mutation should be offered a referral to a specialist genetics service for counselling. For more about genetic testing see genetics of dementia.