Genes do not hold all the answers
If Alzheimer's disease was due to genetics alone then identical twins, who share nearly identical genes, should either both avoid the disease or both get it. In fact studies of twins are beginning to reveal the extent to which environmental factors play a significant role in whether or how Alzheimer's disease starts.
Data from the Swedish Twin Registry shows that if one twin has Alzheimer's disease, 59% of the time so will the other. Whilst this is a fairly high relationship it does pose the question as to why some identical twins are susceptible and others not. Moreover, in a study following male twins who are World War II veterans, it has been found that the age of onset for Alzheimer's may differ by as much as five years in twins who are both diagnosed with Alzheimer's.
Research by Brenda Plassman is directing attention to the environmental factors that might account for this critical five year margin. Factors such as blood pressure, head injury, diabetes, heart disease, stroke and occupational complexity are some of the areas for further investigation.