An email with a black box warning! That’s what I got 11 years ago after Lois and I submitted saliva samples to a DNA testing service. Lois is the family genealogist, and she thought that DNA testing would be helpful in filling in some of the missing branches of our ancestral trees. In addition to lists of DNA relatives, the report included many risk genes for a variety of medical conditions, none of which were present for either of us. However, this locked black box contained two genes of neurological interest. A mutation in the LRRK-2 gene is the most common cause of hereditary Parkinson’s disease, and the APOE-4 allele is the most significant genetic risk factor for late onset Alzheimer’s disease.

Recently, I spoke to a group of medical students about Alzheimer’s disease. I have been giving these talks three or four times a year for the last five years now. I know a lot about Alzheimer’s disease because I am a retired neurologist, and I have treated many patients with dementia, including Alzheimer’s disease. I also know a lot because now I have mild Alzheimer’s dementia. As we’ll see in Chapter 3, Alzheimer’s dementia is the late stage of Alzheimer’s disease when cognitive impairment interferes with activities of daily living. The pathological changes in the brain caused by Alzheimer’s disease begin to appear up to 20 years before the onset of cognitive impairment.