A neurodegenerative disorder characterized by progressive memory loss, spatial disorientation, cognitive dysfunction, and behavioral changes. The pathological hallmarks of Alzheimer's disease include amyloid-beta plaques, tau tangles, and reduced brain glucose uptake. Most cases of Alzheimer's disease do not run in families and are described as "sporadic." The primary risk factor for sporadic Alzheimer's disease is aging, with prevalence roughly doubling every five years after age 65. Roughly one-third of people aged 85 and older have Alzheimer's. The major genetic risk factor for Alzheimer's is a variant in the apolipoprotein E (APOE) gene called APOE4.

One of three common genetic variants of the APOE (apolipoprotein E) gene. The APOE4 allele, which is present in approximately 10-15% of people, increases the risk of developing Alzheimer's disease and lowers the age of onset. Having one copy of E4 increases risk 2- to 3-fold, while having two copies increases risk as much as 15-fold.

Damage to the brain caused by a sudden blow, penetrating injury, or lack of oxygen, ranging from mild to severe. TBIs can induce a wide range of short- or long-term changes in the brain that affect thinking, sensation, language, personality, and emotion. In addition, TBI may increase the risk for developing epilepsy, Alzheimer’s disease, Parkinson’s disease, and other brain disorders. Nearly 75 percent of TBIs that occur each year are concussions or other forms of mild TBI. Even mild TBIs damage the delicate tissues and blood vessels of the brain and can result in altered brain function that can persist for days, weeks, or months. Approximately 15 percent of concussed athletes experience symptoms as long as one year after their injury, a condition called persistent post-concussion syndrome, or PPCS, typically after returning to play too quickly.