Inheritable types of Alzheimer’s disease could be detectable up to 20 years before the onset of memory and cognition problems, new research suggests.

Experts say that by the time dementia symptoms appear, there has already been too much brain damage to reverse or prevent further cognitive dysfunction. However, scientists from the Dominantly Inherited Alzheimer’s Network are following family members of Alzheimer’s patients who have three different gene mutations. These mutations generally indicate a likelihood of developing Alzheimer’s in middle age.

The DIAN investigators say it might be possible to predict the age at which Alzheimer’s will appear based on when a subject’s parent first exhibited symptoms of the disease. This could allow scientists to document a timeline of the disease’s progression even when symptoms aren’t visible, investigators said.

The DIAN researchers noted that new treatments have risks, so it’s crucial that scientists have a firm grasp on who is at risk.

“If we can find a way to delay or prevent dementia symptoms in DIAN participants, that would be a tremendous success story and very helpful in our efforts to treat the much more common sporadic form of the illness,” they wrote in a statement. DIAN plans to start therapeutic trials in familial cases of Alzheimer’s next year.

This research was presented at the recent Alzheimer’s Association International Conference in Paris.