When it runs in the family: putting susceptibility genes in perspective

Using the genetics of late onset Alzheimer's disease (LOAD) as illustrative, this paper argues for a reflexive critique of the involved science, specifically in connection with estimations of increased risk. Following a review of social science commentary on genetic testing and screening in general, current scientific understanding about the molecular and population genetics of LOAD is then presented. The results of open-ended interviews conducted with first-degree relatives of individuals diagnosed with LOAD at two study sites follow. It is shown that the majority of people interviewed embrace the idea of complexity in connection with Alzheimer's disease causation and that many draw on a concept of "blended inheritance" with respect to the disease that "runs" in their family. It is argued that knowledge about risk obtained from genetic testing for LOAD rarely usurps other forms of understanding, but is nested by interviewees into previously held ideas about who in the family is most at risk for the disease.