In Reply.—
Dr Heston has raised several interesting points regarding the methods and conclusions in our recent report concerning the morbid risk among first-degree relatives of patients with Alzheimer's disease. First, he suggests that the risk figures for first-degree relatives over 80 years of age are really not much greater than one would observe in the general population. He states that most population estimates run between 20% and 30% but cites no data. We are aware of no prospective studies indicating such high risks. Some studies indicate prevalence of all types of dementia as high as 22% after 80 years of age,1 but none of them suggests annual risks for Alzheimer's disease as high as the approximately 4% observed in first-degree relatives of Alzheimer's disease probands 80 to 86 years of age.Second, Dr Heston suggests that the risk among control relatives should be substracted from the risk among relatives