Twin brains exhibit similar disease progressions

In a recently published paper in the Journal of Brain Pathology, USC psychologist Margaret Gatz and a team of international experts compared the brains of twins where one or both died of Alzheimer’s disease.

The study, which was funded by research grants from the National Institute of Health, found that Alzheimer’s progressed similarly in the twin pairs, and they both had similar areas of brain damage.

“We try to make inferences based on tests and diagnoses, but we have to assume that what we’re seeing is a manifestation of what’s going on in these twins’ brains,” said Gatz, a professor of psychology, gerontology and preventive medicine in the Dornsife College of Letters, Arts and Sciences, in a press release. “For this reason, we wanted to compare the brains of twins to ask whether identical twins’ brains are actually more identical.”

Over the past 30 years, Gatz has worked with the Swedish twin registry and studied more than 14,000 Swedish twins. For this particular research, scientists autopsied the brains of seven pairs of twins who had previously undergone diagnostic evaluations for Alzheimer’s disease.

“Identical twins tended to have similar combinations of pathologies. We looked not just at the hallmark indicators of Alzheimer’s, but at all the other damage in the brain. Across the whole array of neuropathological changes, the identical twins appeared to have more similar pathologies,” Gatz said in a press release. “This is fascinating: It’s not just a key pathology related to the twins’ diagnoses, but the combination of things happening in their brains. We’re going to keep looking for what these combinations are.”

An autopsy remains the only definitive way to diagnose Alzheimer’s, and though the presence of amyloid plaque and neurofibrillary tangles in the brain are considered hallmarks of the disease, this new study suggests the presence of other factors in the brain could contribute to the start of the disease.

“There may be risk factors that start to accumulate, but don’t lead to a clinical diagnosis,” lead author Diego Iacono of the Karolinska Institute in Sweden and the Biomedical Research Institute said in the press release. “We found that the presence of Alzheimer’s disease doesn’t preclude the presence of other damage.”