There is a web page explaining what is known about heredity and
late onset AD at:

http://www.portfolio.mvm.ed.ac.uk/studentwebs/session3/7/Genetics.htm

I had thought there was no genetic connection in late AD, but
apparently there is one.  The people most at risk are those who
inherit two specific forms of a gene, one from their mother and
one from their father.

However it also appears that having the specific forms of this
gene does not foreordain that a person will get AD.  Other
factors are also involved.

Obviously, all of this research is still evolving.  I'm sure it will
take years to figure it all out.  But we're making progress.  30
years ago nothing of this was known.  In another 20 or 30
years I think our knowledge will be much more complete.  That's
when I expect solid cures to become available.

I'm already old enough that, if I get the disease, there may not
be a cure yet.  But I'm hopeful that my (and everyone else's)
children and grandchildren will be okay.

   Alan