Gene Wilder’s family announced he passed away of “complications from Alzheimer’s disease” at the age 83 in his home in Connecticut on Monday. The iconic actor and comedian suffered privately from the progressive brain disorder for three years before succumbing to the disease’s complications. More than five million Americans are living with Alzheimer’s disease today, but how does this common yet incurable type of dementia kill a person?

Alzheimer’s disease accounts for 60 to 80 percent of dementia cases, which causes problems with memory, thinking, and behavior that slowly worsen overtime. According to the National Institute on Aging, Alzheimer’s is a complex and difficult disease. In the late stages of the condition, patients sufferer from loss of appetite, and lose the ability to to communicate verbally, move without assistance, and recognize family members and friends. However death typically comes as a result from aspiration, pneumonia, infection, or coronary arrest.

Not only does the brain’s ability to think decline overtime, but the ability to maintain life-sustaining homeostasis. Ultimately, the brain affects everything, including the ability to swallow, cough, and breath, leading patients vulnerable to infection and forced to rely on a feeding tube for survival. Unfortunately, hospitalization does not often extend life at later stages of the disease and is, in fact, discouraged because it can prolong suffering without increasing the odds of survival. Interventions such as CPR, feeding tubes, and even dialysis can be of little benefit and may impose greater suffering for the patient.

The advanced stages of Alzheimer’s disease last between an average of 1.5 to 2 years, but for 20 to 30 percent of patients the disease can linger on for as long as 15 or 20 years. According to the Centers for Disease Control and Prevention, it is the sixth leading cause of death in the United States and even those statistics are underestimated because many of the deaths are contributed to pneumonia.

In the end, family members must decide between the sufferer’s quality of life versus quantity. With an incurable disease like Alzheimer’s, choosing to make them as comfortable as possible is preferred, which is why patients are often placed into nursing homes and hospice surrounded by loved ones until their bodies can no longer sustain life on their own.