Nonparticipation in Huntington's Disease Predictive Testing: Reasons for Caution in Interpreting Findings.

When given the opportunity to clarify their genetic status, most individuals at risk for Huntington's disease (HD) currently show a preference not to know. Our understanding of the characteristics of those who do not request HD predictive testing, and the factors influencing their decision, lags behind our knowledge of test applicants. In the light of our experience with interviewing a random sample of nonparticipants in an ongoing study, we critically analyze research concerning the differences between participants and nonparticipants in HD predictive testing programs and the interpretive characterization of these two groups. The findings concerning nonparticipants are limited to a small sample of the at-risk population, with the problems of biased samples and low response rates. We discuss this and other aspects of research in this area, notably the context and timing of data collection and the predominantly questionnaire-based methodology, that lead us to interpret the conclusions drawn about these two groups with caution.