Alzheimer’s disease can seem frightening, mysterious and daunting. There are still a lot of unknowns about the disease, which afflicts more than five million Americans. Here are answers to some common questions:

Sometimes I forget what day it is or where I put my glasses. Is this normal aging, or am I developing Alzheimer’s?

Just because you forgot an item on your grocery list doesn’t mean you are developing dementia. Most people have occasional memory lapses, which increase with age. The memory problems that characterize warning signs of Alzheimer’s are usually more frequent, and they begin to interfere with safe or competent daily functioning: forgetting to turn off the stove, leaving home without being properly dressed or forgetting important appointments. Beyond that, the disease usually involves a decline in other cognitive abilities: planning a schedule, following multistep directions, carrying out familiar logistical tasks like balancing a checkbook or cooking a meal. It can also involve mood changes, agitation, social withdrawal and feelings of confusion, and can even affect or slow a person’s gait.

How is Alzheimer’s diagnosed?

Diagnosing Alzheimer’s usually involves a series of assessments, including memory and cognitive tests. Clinicians will also do a thorough medical work-up to determine whether the thinking and memory problems can be explained by other diagnoses, such as another type of dementia, a physical illness or side effects from a medication. Brain scans and spinal taps may also be conducted to check for corroborating evidence like the accumulation of amyloid, the hallmark protein of Alzheimer’s, in the brain or spinal fluid.

What causes Alzheimer’s?

The cause is unknown for most cases. Fewer than 5 percent of cases are linked to specific, rare gene mutations. Those are usually early-onset cases that develop in middle age. In the vast majority of cases, Alzheimer’s disease makes its presence known after age 65, and the older one gets, the greater the risk. Aside from age, which is the single biggest risk factor, there are health issues that can increase the chances of developing Alzheimer’s. Heart and vascular problems, including stroke, diabetes and high blood pressure, appear to increase the risk of Alzheimer’s and other dementias. Depression has also been associated with increased risk.

People with one copy of the ApoE4 gene variant have two to four times as much risk of developing Alzheimer’s as people without the variant, and people with two copies of ApoE4 have about 10 times the risk. That risk appears to be larger in women. Carriers of ApoE4 also have a greater chance of developing symptoms at a younger age. About 25 percent of people have one copy of ApoE4; about 3 percent have two copies.