A new study suggests that Alzheimer’s disease may affect the brain differently in black people compared with whites.

The research, conducted by Lisa L. Barnes at the Rush University Medical Center, suggests that African Americans are less likely than Caucasians to have Alzheimer’s disease alone and more likely to have other pathologies associated with dementia. These include the presence of Lewy bodies, which are abnormal proteins found in the brain, and lesions arising from the hardening of tiny arteries in the brain, which is caused mainly by high blood pressure and other vascular conditions.

Handout image: Tau lesions and senile plaques in Alzheimer’s disease. (Neuron, Maruyama et al.)

The findings suggest that researchers should seek different strategies to prevent and treat Alzheimer’s disease in blacks. While many therapeutic strategies focus on removing or modifying beta amyloid – a key ingredient whose accumulation leads to the chain of event triggering the neurodegenerative disease – the study suggests that possible treatments should pursue additional targets, particularly for African Americans.

But the study also points up the critical need to enroll more black people in clinical trials. Although Barnes said the research was the largest sample of its kind, she also acknowledged that the sample is still small. And that’s at least partially because blacks, for a variety of cultural and historical reasons, are less likely to participate in scientific research.

“It’s not for lack of trying,” Barnes said in an interview. She said scientists must to a better job of earning the trust of African Americans and enrolling more of them in medical research.

The study, which appeared Wednesday in the medical journal Neurology, involved the post-mortem examination of the 122 brains, including 41 that had belonged to African Americans diagnosed before death with Alzheimer’s disease. These were then compared with cadavers’ brains from 81 Caucasians who also had Alzheimer’s disease.

Researchers examined the brains looking for signs of Alzheimer’s disease, such as the distinguishing plaques and tangles caused, respectively, by buildup of beta amyloid and tau proteins in the brain, or the presence of Lewy bodies. Named after their discoverer in 1912, Lewy bodies disrupt the brain’s normal functioning, sometimes producing hallucinations, delirium and other dramatic changes in a person’s behavior, including body rigidity and trembling that resembles Parkinson’s disease. The condition affects an estimated 1.3 million Americans.

The researchers found that about half of the Caucasians showed evidence of Alzheimer’s alone, while less than 25 percent of African Americans displayed evidence of Alzheimer’s pathology alone. Yet 71 percent of African Americans had Alzheimer’s disease mixed with evidence of other brain-damaging pathologies, such as Lewy bodies or dead tissue caused by inadequate circulation. That compared with 51 percent of Caucasians with multiple pathologies.

Barnes acknowledged that besides having only a small sample, the cadavers with Lewy bodies may also have been overrepresented because of selection bias: because of the more dramatic symptoms involved with their presence – as compared with gradual memory loss – it’s possible that blacks with Lewy body disease are more likely to seek medical attention. Owing to cultural factors, African Americans are more likely not to seek medical attention for Alzheimer’s disease symptoms such as memory loss because of widespread belief that those symptoms are a normal part of aging.

African Americans also lag behind whites in scientific trials because of socioeconomic and cultural reasons. Their access to health care is more limited, and many blacks are still distrustful of researchers because of historical abuses such as the 1932 Tuskegee medical study, in which the federal government enlisted about 400 low-income black men suffering from syphilis without informing them of their options and allowed some to go untreated after penicillin became available.