Scientists in North America claim to have found a gene that causes a common form of dementia.
Researchers claim that a mutated gene can cause an inherited form of frontotemporal dementia (FTD).
The illness is responsible for around 15 per cent of all dementia cases, with around half of all instances hereditary.
Dr Ian Mackenzie, a neuropathologist at the University of British Columbia, who helped uncover the mutated gene, commented: "We've discovered the genetic cause of an important inherited type of dementia.
"The immediate implications are that we can now begin to offer genetic counselling and genetic testing for affected families."
Like Alzheimer's Disease, FTD is currently incurable, although its symptoms, which include changes in personality and behaviour, come on at an earlier stage, typically for people in their 50s and 60s.
Dr Mackenzie told the Globe & Mail that those with the condition can become very withdrawn and emotionally blunt or they may become emotionally uninhibited.