Alzheimer’s disease (AD) is the most common type of dementia. Dementia is a generic term for conditions that occur when the brain no longer functions properly. Worldwide, at least 44 million people are living with dementia, making the disease a global health crisis. Like me, you probably know someone who has been affected by this condition. What’s surprising is that this isn’t a disease of ageing and that only 1% of cases are caused by genes. Scientists now know a lot about AD, and preventive therapies probably aren’t far off. But even when they become available, such therapies will almost certainly be very costly and involve drugs with probable side effects.