Researchers have found dementia resistance runs in the family in a study at the Mount Sinai School of Medicine, New York.
It was observed that individuals who are free of dementia and have high levels of a protein indicating inflammation are less likely to have relatives with dementia.
Dr Jeremy M Silverman, author of the study, explained: "In very elderly people with good cognition, higher levels of C-reactive protein, which is related to inflammation, are associated with better memory."
It was also identified that a lower dementia risk was also prevalent in parents and siblings.
The discovery was made when researchers tested 277 male veterans aged 75 and over who were free of dementia for the C-reactive protein. They then checked relatives for the condition and only 40 people from 37 families had dementia.
In a secondary investigation, 202 relatives were tested for the condition and only nine had cognitive impairment.
Understanding the genetic risks for dementia will prove key in understanding its causes further and developing more effective treatments.
Find out about dementia care and support services at Barchester care homes.