Scientists do not yet fully understand what causes Alzheimer’s disease. There probably is not one single cause, but several factors that affect each person differently. In short, the causes of Alzheimer’s disease are unknown.

Age is the most important known risk factor for Alzheimer’s disease. The number of people with the disease doubles every 5 years beyond age 65. Please don’t confuse the association of age with Alzheimer’s — Alzheimer’s disease is not a part of normal aging. Rather, it is a disease that affects a minority of people as they age.

Family history is another risk factor. Scientists believe that genetics may play a role in many Alzheimer’s disease cases. For example, familial Alzheimer’s disease, a rare form of Alzheimer’s disease that usually occurs between the ages of 30 and 60, can be inherited. However, in the more common form of Alzheimer’s disease, which occurs later in life, no obvious family pattern is seen. One risk factor for this type of Alzheimer’s disease is a protein called apolipoprotein E (apoE).

Everyone has apoE, which helps carry cholesterol in the blood. The apoE gene has three forms. One seems to protect a person from Alzheimer’s disease, and another seems to make a person more likely to develop the disease. Other genes that increase the risk of Alzheimer’s disease or that protect against Alzheimer’s disease probably remain to be discovered.

Scientists still need to learn a lot more about what causes Alzheimer’s disease. In addition to genetics and apoE, they are studying education, diet, environment, and viruses to learn what role they might play in the development of this disease.

More recent research suggests that the chloresterol gene — ApoE4 — may impact one’s susceptibility for Alzheimer’s. Another recent study suggests that Alzheimer’s may also be linked to an overactive immune system. Confused? So are scientists.

One warning sign for Alzheimer’s may be reduced computer activity as a person ages.

If you believe you or a loved one may have increasing problems with memory (especially memory for recent things, rather than things in a person’s past), it’s a good idea to have it checked out. Talk to your doctor, who may give you a referral to a specialist, such as a geropsychologist — a psychologist who specializes in working with seniors. While the process may be daunting or even scary to consider, it’s better to have the information available.

Such information can help inform next steps in learning techniques to make up for the memory issue (writing a lot more things down, for instance, and keeping a daily calendar of activities). Plus it will help with the effort of longer-term planning, especially if it turns out to be Alzheimer’s.