Not yet but this is probably a good thing seeing that it would depend
on a cerebral spinal fluid tap.  :-o  Genetic markers are another
possibility but are also not practical for the do-it-yourselfer...From
an insurance point of view, perhaps difficult tests are a good thing.

Mary G. wrote a wonderfully concise reply a while ago regarding
"Heredity and AD"  Here's the post...use google > groups to search for
the full thread

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Irrespective of family history, about 5 in 100 people have Alzheimer's
at age 65. By age 80, these odds increase to 1 in 5. By age 90, nearly
half of all people have some symptoms of dementia, so just being lucky
enough to live to an advanced age is the biggest risk factor, never
mind your genes. Only 3% of all cases of Alzheimer's have a proven
hereditary link.

The two basic types of AD are familial and sporadic. Familial AD (FAD)
is relatively rare affecting less than 10 percent of AD patients - it
often gets called early onset Alzheimer's. It is associated with gene
mutations on chromosomes 1, 14, and 21. FAD is the result of a certain
inheritance pattern called autosomal dominant. In this pattern, all
offspring in the same generation have a 50/50 chance of developing AD
if 1 of their parents had it - so its similar to Huntington's disease.
FAD occurs in younger people - usually before age 60 - so it is a form
of dementia that tends to hit people in middle age. If this was in
your biological relatives, you would likely be hearing stories about
people who went downhill while still in the theoretical prime of life
- their 40's, 50's or 60's, not just in their senior years. At least
forty percent of people who develop early-onset Alzheimer's have a
family history of the disease.

Garden variety onset AD is usually refered to Sporadic AD and usually
occurs later in life, is far more common than FAD, and appears to be
related to the apoE gene found on chromosome 19. ApoE comes in several
different forms or alleles, but three occur most frequently. People
inherit one allele (apoE2, apoE3, or apoE4) of the apoE gene from each
parent. People with both apoE3 and apoE4 alleles (E3/E4) are affected
by both alleles. Having one or two copies of the E4 allele increases a
person's risk of getting AD. Having the E4 allele is a risk factor for
AD, but it doesn't mean a person is doomed to get it -some people with
two copies of the E4 allele (the highest risk group) don't get AD and
others with no E4s do. So, the jury is out on the exact degree of risk
of AD for any given person based on apoE status.

There was one that made the news about 5 years ago and then
again(same test) about 3 years ago. It was just the company that
made it doing a PR run with a test that didn't really give you
good results. If you are interested look thru this group on
Google. You'll at least find the company but I don't know if they
make it anymore.