The two largest studies ever conducted of Alzheimer's disease have proven that five new genes make the disease more likely in the elderly, providing clues as to what starts Alzheimer's and allows it to take over the brain. An international analysis of more than 50,000 people found that the new genes build on a possible theme: So far genes that increase Alzheimer's risk in the elderly tend to be connected to cholesterol and inflammation. "The level of evidence is very, very strong," said Dr. Michael Boehnke, a professor of biostatics at the University of Michigan who does similar studies in diabetes and bipolar disorder. While the new genes are clearly linked to Alzheimer's, each gene only increases risk of inheriting the disease by 10 to 15 percent. But even these small numbers will prove helpful for understanding the disease and developing new therapies and treatments, researchers say.