Preliminary examination of disgust learning as a potential OCD endophenotype

Endophenotypes (intermediate phenotypes) are traits hypothesized to represent genetic risk for disorders such as OCD. However, it is unclear if disgust conditioning abnormalities may function as an OCD endophenotype. The present study sought to examine the extent which disgust conditioning abnormalities characterize OCD in a manner that is consistent with an endophenotype. Participants with OCD (n = 30), first-degree relatives (n = 27), and unrelated age-matched healthy controls (n = 25) completed a disgust conditioning task in which one neutral food item (conditioned stimulus; CS+) was followed by disgusting videos of individuals vomiting (unconditioned stimulus; US) and another neutral food item (CS-) was not reinforced with the disgusting video. Following this acquisition phase, there was an extinction phase in which both CSs were presented unreinforced. As predicted, the CS+ was rated as significantly more disgusting than the CS- after two blocks of acquisition and this pattern was eliminated after extinction. Although no group differences emerged as a function of the CS+ compared to the CS-, the OCD group reported statistically significantly higher disgust ratings to both CSs during acquisition (but not at habituation or extinction) than relatives and controls. However, relatives and controls did not significantly differ from each other. Additionally, disgust proneness explained the group difference between those with and without OCD in disgust responding to both CSs at acquisition. These findings suggest a readiness for disgust conditioning in OCD that may be the product of heightened disgust proneness but provide no evidence that it functions as an endophenotype.