When is the correct time to diagnose dementia?

Pin-prick blood tests that detect possible precursors of Alzheimer's disease are becoming available - but is it right to label people who will never develop the disease?

It's difficult to say when he first began noticing the signs, says Chris. He was living abroad and communicated with his parents on Skype. During these calls, his mother would sometimes repeat herself, asking the same question just minutes later. We didn't think much of it, we assumed it was due to technical problems." Then his father mentioned that there was something wrong with her memory. Mum being only 63, I didn't believe him." But two years later, during a Christmas break abroad, when his mother went upstairs to use the toilet and couldn't find her way back down, they knew there was something up.

Shirley was diagnosed with Alzheimer's disease at the age of 67 by a GP using a cognitive test that includes drawing a clock with a certain time on a piece of paper. She received the diagnosis via a letter that consisted of only one line. I look at that letter and I am appalled by it," says Chris. My mother never saw a neurologist. It was such a thin diagnosis. We thought this can't be right, she's too young."