What were the early signs?

My mother-in-law died a few years back after a couple of years with a particularly nasty form of dementia, but hers was not the more typical Alzheimers. Hers was very geographical at first. She couldn't find familiar places while driving her car, then she couldn't find rooms in her own house -- that sort of thing. My father in law hid it from the rest of us for a long time.

My own mother has recently had a string of experiences that are making me wonder if she's in the early stages of dementia (her father had it). She's in her late 70s.

Anyone have any words of wisdom, things I should watch for? My dad is living and healthy. They live 2000 miles away from me, but they might be amenable to moving close by if they needed help.