People whose parents are diagnosed with Alzheimer's disease are at higher risk of developing the condition. A new study shows that the disease occurs very early in these people, often years before any symptoms begin to appear.

Alzheimer's disease is characterized by loss of memory and a significant decline in cognitive skills. Over five million people in the U.S currently have this condition. There is no cure for the disease, according National Institute on Aging.

"Studies show that by the time people come in for a diagnosis, there may be a large amount of irreversible brain damage already present," said study author Lisa Mosconi, PhD, with the New York University School of Medicine in New York. "This is why it is ideal that we find signs of the disease in high-risk people before symptoms occur."

The study included 52 people between 32 and 72 years. The participants were dementia-free at the start of the research. They underwent several brain scans.

Participants were then split into various groups depending on Alzheimer's disease history in the family; those who had a mother with AD, a father with AD, both parents with the disease or none with the disease, according to a press release.

People whose parents had Alzheimer's disease had five to ten percent increased levels of plaque and several brain abnormalities than people in the other three groups. Also, people whose mothers had AD were more likely to show these changes in brains than those whose fathers had this condition.  

 "Our study also suggests that there might be genes that predispose individuals to develop brain Alzheimer's pathology as a function of whether one parent or both parents have the disease," Mosconi said in the news release. "We do not yet know which genes, if any, are responsible for these early changes, and we hope that our study will be helpful to future genetic investigations."

The study is published in the journal Neurology.