Expert: Mary Gordon - 5/15/2007

Question
what are the chances of passing the  trait to your offspring? What steps could you take to determine if your children could have the disease before you plan a family?What are some methods of passing the trairt to an offspring?

Answer
First off, you should realize there are many, many causes of dementia in the elderly -i.e. not every elderly person with cognitive and memory impairments has Alzheimers. In fact, if you are lucky enough to live until your mid 80's, your odds of having some form of cognitive impairment is better than 50-50. Those odds are true for everyone, not just those with specific dementias in their family tree.

The only form of Alzheimer Disease (AD) which appears to have a definite
genetic link is known as Familial Alzheimer Disease (FAD). FAD forms only a
very small minority of all cases of AD.  Members of these families have a
50.0% probability of developing AD and it usually appears quite young - often in middle age. If you had this in your family, you would know about it as you would be aware of a strong pattern of family members having to be institutionalized, retire very young, going "crazy", etc. etc. in their 40,s, 50's or 60's.  

There are also early onset forms of the disease that do not show the striking inheritability (i.e. they are random, not necessarily genetic).  

The most common form of AD is Sporadic Alzheimer Disease (SAD). This is the garden variety - the odds of getting this get higher with age for everyone.

There are no scientific studies which can either prove or disprove with
certainty the role of genetics in SAD at the present time.  Although several
genes have been identified as having the potential to increase the risk of
developing AD, they are not the only factors which influence SAD.   The predictive value of genetic testing is not at a level at the present time which would benefit the persons having the test (i.e. they can't give you a yes/no answer).

The gene which has recieved the most attention is the APOE gene.  Each gene
is composed of two alleles (one inherited from the mother and one from the
father).  There are three different alleles, the APOE2, APOE3 and APOE4.
The APOE4 allele is thought to carry the higher risk whereas the APOE2
carries the lower risk.  Persons with the APOE4-APOE4 gene combination are
thought to have the highest risk while persons with the APOE2-APOE2
combination have the lowest.

The problem with the pure genetic theory is that some persons with the
APOE4-APOE4 combination (highest risk) do not develop AD while some persons with the APOE2-APOE2 combination (lowest risk) do.  It is for this reason that research is investigating potential environmental factors which may be triggers of the disease.  Except for FAD, there is nothing which can be
proved or disproved with certainty at the present time.  There is some
debate as to whether or not FAD and SAD are the same disease or two separate diseases with a similar pathology.

What it comes down to at present is that we're pretty much all in the same boat when it comes to Alzheimers and other forms of dementia.  The best thing any of us can do is exactly what our family doctors and moms have been telling us forever. Keep your weight down, exercise, keep your blood pressure and blood sugars under control, eat well, get lots of rest, don't smoke, stay active and be moderate with alcohol. That is the best overall way to help up your odds to a long healthy life with marbles intact.

http://www.alzheimers.org.uk/Facts_about_dementia/Genetics/info_genetics.htm

Hope this helps

Mary