Hi Jillywak,
Welcome to TP about 10yrs ago I was in the same boat as you, except it was my Dad. Dad was diagnosed at around age 54 with early-onset Alzheimers disease. My advice with hindsight (this is going to be long):
1. Start taking what doctors say with a grain of salt as they definitely don't know everything about dementias. Doctors may call it Alzheimers disease but it could be one of a great multitude of dementia types...general doctors don't usually know much about the different types and some might even tell you it is genetic when they don't really know...(one or two did to me)Its better to do your own research when it comes to this diagnosis, because often we the carers are the ones who end up suggesting possible medicines, or alternative diagnoses (usually still a dementia type however).
2. Its not always about memory problems. Although it sounds from what you say that your mother has memory problems, be aware that it can be the case that memory is not always affected by this disease. It depends on what part of the brain is affected...it can seem like memory problems, i.e. Dad seemed to forget how to talk...but it's just that he can't get the language part of his brain to work. It doesn't seem like much of a difference, but it can help to be aware of this when managing strange behaviours. I.e. Being afraid to walk through a shadow is not representative of a memory problem but a change in either visual perceptions or emotions.
3. Enjoy the now. As a few on here have already mentioned, it is important to make the most of today. It is very easy to get caught up in the distress of seeing your parent's decline and focus on all the things they can't do anymore. But with hindsight it would be far better to focus on all the things they can still do and enjoy it. I was majorly distressed by my Dad not being able to tie his tie, but now I look back and think how well he was back then and I didn't even realise it. With this I also advise taking lots and lots of photos, always...because you don't realise how great things are till its too late. That sounds depressing in its own way...sounds like the future is very grim...but after you've dealt with this disease, its more about the fact that there are so many changes that can come with this disease and you learn to love the new person you get each time and its great to have memories of all those times.
4. Think very hard about what you want from life before giving it up. I know it seems terrible to consider leaving your mum for the south of France right now....but maybe now is a good time to do that. Its a hard decision however...if you leave now you may miss out on enjoying how she is now, but then if you don't go now, you may not get another chance to do something like that for many many years. Some people have a rapid decline with this disease and others have a slow decline...Dad initially had a slow decline and then about 3yrs after diagnosis he went rapidly downhill, but its been about 10-11yrs now, and I lost most of my 20s to it. Other people seem to not carry on with this disease as long. You have to consider your husband, your children and also what your mother would have wanted for you. If you have a brother who is close by and willing to help out, could you move to France for a few years, visit regularly, with an expectation that you might have to move back...?
5. Medicines. Medicines to investigate are Aricept, Ebixa, Reminyl/Galantamine, Memantine to name a few. Aricept seems to be the most common one for trying to slow the disease down. The medicines may have different names depending on what country you live in, and some are for early stages and others are for later stages. Again don't just rely on a gp to know what medicines are best.
6. Try not to stress too much about the genetics. Whilst caring you may start to really worry about this as the stress of caring can cause similar symptoms. Statistics are such that most of these dementias are not hereditary. Does your Mum have brothers and sisters, did any of them get this disease? Also I am guessing that you have probably about 20yrs before you really have to start to worry, so there's a lot that might happen with medications and cures before then. If anything, use any such fear to not rule your life but to make it better, use it to make sure that you enjoy your life now, every day of it.
7. Investigate the legal and other issues now. A power of attourney will be needed so that someone can manage your Mum's affairs (i.e. money and property matters) when she is no longer able to. It can be shared so perhaps both you and your brother can share it, to avoid any family angst.
Well thats enough for now...if you need any specific support, or not so specific support (i.e. to have a good cry) feel free to private message me anytime.
Best of luck,