There is sometimes a fine line between a joke and simply an odd, inappropriate comment. Now new research shows that changes in a person’s sense of humor could be an early warning sign of the onset of dementia.

The research published in the Journal of Alzheimer’s Disease found that such changes in humor could occur before other warning signs, according to Tech Times. Most researchers have focused on memory loss in dementia, but for patients with frontotemporal dementia (FTD), the most common form of the disease among those under age 55, typically behavioral and personality changes occur before other symptoms appear.

The new research from the University College London found that those patients with FTD had significant changes in their understanding of humor, with many laughing at inappropriate times or favoring more childish types of humor while losing their sense of more sophisticated varieties. They noted that according to family and friends of those afflicted with FTD, the patients manifested the humor changes on average nine years before other symptoms appeared.

The British study surveyed friends and family members of 48 FTD patients, asking about specific types of humor such as Mr. Bean or Monty Python. One patient was described as suddenly having a darker and more troubling sense of humor, while a friend of another said the patient’s humor had been dulled.

A son of one FTD patient who was not followed for the study nonetheless noted that his mother’s troubles began when she lost her emotional connections to people and became more detached, including laughing when others had accidents or misfortunes, all very atypical behaviors for her.

The study’s lead author noted that the work showed the importance of tracking behavioral and personality changes even more than memory loss. A researcher from the organization Alzheimer’s Research UK noted the importance of looking at the totality of symptoms in order to determine an accurate diagnosis.