What are the causes Alzheimer's disease?

Undrestanding the causes of the Alzheimer's disease is an ongoing research. The research so far indicate that causes probably include a combination of age-related changes in the brain, along with genetic, environmental, and lifestyle factors. The importance of any one of these factors may differ from person to person. 
One well-known gene that influences Alzheimer’s risk is the apolipoprotein E (APOE) gene, which has been identified via Genome Wide Association Studies (GWAS). The APOE gene is involved in making a protein that helps carry cholesterol and other types of fat in the bloodstream.