Gene Predicts Risk for Alzheimer’s Disease Symptoms after Traumatic Brain Injury, Penn Study Finds

The presence of a gene can predict when a traumatic brain injury (TBI) will lead to early symptoms of Alzheimer’s disease, according to a new study from neuroscientists at the University of Pennsylvania School of Medicine. Amyloid plaque deposits, known primarily for their role in Alzheimer’s disease, are found in nearly one third of people who die from acute TBI, within just hours of a brain injury and in people of all ages. This build up of Alzheimer’s-like deposits can be predicted by a variation in the gene that codes for the amyloid-busting enzyme, neprilsyin.

A single traumatic brain injury (TBI) has emerged as an important risk factor for the later development of Alzheimer’s disease. While plaques in Alzheimer’s disease develop slowly over time and almost exclusively in the elderly, the same pathology can be found rapidly following TBI.

"These findings may be very important for individuals at high risk of TBI, such as participants in contact sports or military personnel,” said senior author Douglas Smith, MD, director of the Penn Center for Brain Injury and Repair and professor of Neurosurgery at the University of Pennsylvania School of Medicine. “A genetic screening tool may be useful in identifying those at risk of developing Alzheimer’s-like amyloid plaques following a traumatic brain injury."

The amyoid-degrading protein, neprilysin, has been found in abundance following TBI. Variations in an individual’s ability to produce effective neprilsyin may explain why some people generate plaques while others do not.

Researchers looked at genetic samples from 81 head-injured victims who had died acutely following brain trauma between 4 hours and 25 days following their injuries. As expected, in around a third of cases, amyloid deposits were found throughout the brain, similar to what is seen in early Alzheimer’s patients. Researchers found that variations, known as polymorphisms, in part of the neprilysin gene correlated strongly with the presence of these plaques. The study appeared in the Journal of Neurotrauma.

Future studies may investigate whether these genetically predisposed individuals are the same people who go on to develop Alzheimer’s disease after TBI.