Purpose: To examine why so few individuals at risk of Huntington disease (HD) seek genetic testing and why the propensity to test increases with the belief of carrying the gene.
Methods: HD is an inherited disorder generally characterized by the adult onset of impaired movement and cognitive decline that commonly leads to institutional care and eventually death within 20 years. A genetic test that can confirm or rule out with near-certainty whether an individual will develop HD is inexpensive and widely available. As the disease has no cure, the test does not help improve treatment but it can guide individuals in their decisions about education, marriage, fertility, savings, and retirement. Given the disease’s substantial mortality and morbidity impact, neo-classical models predict that individuals at risk of HD value genetic testing highly, yet fewer than 10% opt for the test. Moreover, the propensity to test has been observed to increase with individuals’ belief that they will develop HD, contradicting neo-classical predictions. Using survey data from 64 untested individuals at risk of HD (mean age: 44 years; 42% male; 84% white; mean years of education: 14.5), we test whether respondents' stated advantages and disadvantages of testing for HD reveal an asymmetry between the perceived loss in utility of confirming the eventual onset of HD and the perceived utility gain of ruling it out. We also test whether the stated advantages and disadvantages of testing vary with respondents’ experience of symptoms, which inform their beliefs about HD.
Results: 53% of respondents feared “depression after confirming HD”, while only 5% of respondents explicitly mentioned the possibility of “feeling much better” after ruling it out. Moreover, after controlling for respondent demographics, symptomatic respondents were substantially and significantly less likely than non-symptomatic respondents to fear depression after confirming HD (-36 percentage points, p=0.006), while respondents rarely considered the possibility of “feeling much better” as an advantage of testing regardless of symptom onset (-4 percentage points, p=0.439). We show that a simple modification of the neo-classical model in which individuals assign greater weight to losses relative to gains can account for these survey response patterns.
Conclusion: Survey responses of individuals at risk of HD are consistent with Prospect Theory, in which subjects systematically overweight the losses relative to the gains of genetic testing.