Claim: Ronald Reagan had a disease that affected his memory.

Alzheimer 's disease -LRB- AD -RRB- , also referred to simply as Alzheimer 's , is a chronic neurodegenerative disease that usually starts slowly and worsens over time . It is the cause of 60 % to 70 % of cases of dementia . The most common early symptom is difficulty in remembering recent events -LRB- short-term memory loss -RRB- . As the disease advances , symptoms can include problems with language , disorientation -LRB- including easily getting lost -RRB- , mood swings , loss of motivation , not managing self care , and behavioural issues . As a person 's condition declines , they often withdraw from family and society . Gradually , bodily functions are lost , ultimately leading to death . Although the speed of progression can vary , the average life expectancy following diagnosis is three to nine years .   The cause of Alzheimer 's disease is poorly understood . About 70 % of the risk is believed to be genetic with many genes usually involved . Other risk factors include a history of head injuries , depression , or hypertension . The disease process is associated with plaques and tangles in the brain . A probable diagnosis is based on the history of the illness and cognitive testing with medical imaging and blood tests to rule out other possible causes . Initial symptoms are often mistaken for normal ageing . Examination of brain tissue is needed for a definite diagnosis . Mental and physical exercise , and avoiding obesity may decrease the risk of AD ; however , evidence to support these recommendations is not strong . There are no medications or supplements that decrease risk .   No treatments stop or reverse its progression , though some may temporarily improve symptoms . Affected people increasingly rely on others for assistance , often placing a burden on the caregiver ; the pressures can include social , psychological , physical , and economic elements . Exercise programmes may be beneficial with respect to activities of daily living and can potentially improve outcomes . Treatment of behavioural problems or psychosis due to dementia with antipsychotics is common , but not usually recommended , as there is little benefit with an increased risk of early death .   In 2015 , there were approximately 29.8 million people worldwide with AD . It most often begins in people over 65 years of age , although 4 % to 5 % of cases are early-onset Alzheimer 's which begin before this . It affects about 6 % of people 65 years and older . In 2015 , dementia resulted in about 1.9 million deaths . It was first described by , and later named after , German psychiatrist and pathologist Alois Alzheimer in 1906 . In developed countries , AD is one of the most financially costly diseases .