About half the carriers of a gene variant called APOE 4 get dementia. But scientists don't know why the other half don't. It may be all in your attitude. Researchers surveyed 1, 250 older adult carriers of APOE 4 gene variants on their beliefs about aging. They presented statements such as "True or False: The older I get, the more useless I feel" Those who were most positive about aging were significantly less likely to develop dementia over the next four years. In fact, their risk for dementia was the same as if they didn't carry the risk increasing gene variant at all.
Source: PLOS One