" Among the risk factors for Alzheimer’s disease having and APOE gene is a risk factor, having a diagnosed family member is a risk factor. They are roughly the same magnitude of risk. The most important risk factor however is age. You have to live long enough to be at risk and the APOE gene has an effect on what age you are when you develop Alzheimer’s disease. So if I have no copies of APOE4 and I develop Alzheimer’s disease my average age of on-set is roughly 80. If I have one copy of APOE4 and I develop Alzheimer’s disease I will be in my mid 70s. If I have two copies my average age is in my late 60s. If your loved on developed Alzheimer’s at an early age, I would consider getting genetically tested. "