Question:
I have a friend whose mother is in the final stages of alzheimers, and willprobably die this month. My friend is worried that she might have inheritedthe genetics that will put her in the same position 20 or 30 years from now.

Is there any study that proves (or disproves) a genetic link to Alzheimers?I would like to be able to direct her to a web page that DISPROVES apotential hereditary link to that disease. I'm sure it will make her feelmuch better.

Answer: The ApoE gene, E4 form, poses a genetic risk to developing Alzheimer's.It's only responsible for a small percentage of AD though (~10%?). Itseems to be a much milder form of AD, with lower mortality rates, slowercognitive decline, and less likelihood of Parkinson type movementdisorder development. At least according to the predictors study, nowentering phase II.

The only form of Alzheimer Disease (AD) which appears to have a definitegenetic link is known as Familial Alzheimer Disease (FAD). FAD forms only avery small minority of all cases of AD. Members of these families have a50.0% probability of developing AD and it usually appears before the age of65. It is important to make the distinction between early-onset AD (beforethe age of 65) and late-onset AD (after the age of 65). Early-onset AD doesnot automatically indicate FAD. The most common form of AD is SporadicAlzheimer Disease (SAD).

There are no scientific studies which can either prove or disprove withcertainty the role of genetics in SAD at the present time. Although severalgenes have been identified as having the potential to increase the risk ofdeveloping AD, they are not the only factors which influence SAD. Genetictesting is not an option in Canada except for research purposes because ofthe ethical issues involved. The predictive value of genetic testing is notat a level at the present time which would benefit the persons having thetest.

The gene which has recieved the most attention is the APOE gene. Each geneis composed of two alleles (one inherited from the mother and one from thefather). There are three different alleles, the APOE2, APOE3 and APOE4.The APOE4 allele is thought to carry the higher risk whereas the APOE2carries the lower risk. Persons with the APOE4-APOE4 gene combination arethought to have the highest risk while persons with the APOE2-APOE2combination have the lowest.