US scientists say new treatments for Alzheimer's disease may need to be developed for African-American sufferers.

Alzheimer's disease may affect the brain differently in African-Americans than white Americans of European descent, US scientists say.

Researchers say their findings suggest a need for different types of Alzheimer's prevention and treatment in African-Americans.

Alzheimer's disease is the most common cause of dementia and sees proteins build up in the brain to form structures called plaques and tangles.

US scientists looked for these plaques and tangles in the brains of people who had died, as well as other brain changes that can cause dementia.

These include infarcts (tissue death) associated with stroke, and Lewy bodies (tiny deposits of protein in nerve cells) seen in Parkinson's disease.

They found that only about half of the European-Americans had pure Alzheimer's disease pathology, while the rest also had infarcts or Lewy bodies in their brains.

In contrast, fewer than 25 per cent of the African Americans had pure Alzheimer's disease pathology, while in three-quarters it was mixed with another type of pathology.

"Because some studies suggest that Alzheimer's disease is more common among older African-Americans than European-Americans, we wanted to see whether the brain changes caused by Alzheimer's are different in these two racial groups," said study author Lisa Barnes, associate professor at Rush University Medical Centre in Chicago.

"Current Alzheimer's drugs primarily target specific Alzheimer pathologies in the brain.

"Given the mixed pattern of disease that we see in African-American brains, it will be important to develop new treatments that target these other common pathologies, particularly for African-Americans."