In a major new development, researchers have found the gene that causes the most aggressive form of Alzheimer's Disease. Scientists say the discovery could help show what goes wrong in the brain to cause the illness' more general forms. Although the news is a major step forward, its immediate impact is very limited, saysTIME Science writer Christine Gorman. "This gene is only for a very rare form of the disease. But there are a number of genes that cause what is lumped together as Alzheimer's. What researchers hope is that this discovery will lead toa general understanding of all the factors involved in the disease."