It is not known exactly why people develop Alzheimer's disease, but it's likely to be caused by a combination of factors. The main risk factor for developing Alzheimer's disease is age. About half of people with Alzheimer's disease have parents, brothers or sisters who have it. There are some inherited risk factors that make you more likely to get Alzheimer's disease, but these don't mean that you will definitely do so. Eg, inheritance of certain genes appears to increase the likelihood of developing Alzheimer's disease. Other factors that make you more likely to develop Alzheimer's disease include previous head injury, a low level of education, high blood pressure and high cholesterol levels. Women are more likely to develop the disease than men.
Attribution: BUPA