Delay discounting: Discussion on an endophenotypic diagnostic tool in anorexia nervosa

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Delay Discounting (DD) is a cognitive process that allows an individual to depreciate the value of a reward depending on variable delay times. Some studies have evaluated this process in Anorexia Nervosa (AN) and have identified that these patients were able to discount the value of a reward over time significantly less steeply than healthy control (HC), reflecting a stronger self-control as it could be in food intake. The aim of this study is to show that the results found in the DD task constitute a potential marker in AN and particularly in its restricting subtype (AN-R). Patients with AN meeting criteria for AN-R restricting subtype (n = 21, AN-R) or binge-purge subtype (n = 21, AN-BP), patients with bulimia nervosa (n = 21, BN) and healthy control (n = 20, HC) performed a delay discounting task consisting of a range of 60 monetary choices with variable delay times. Statistical analysis were performed using the final amounts chosen at the end of each test, indicating the “indifference points”. As expected, patients with AN-R significatively depreciated less the value of a monetary reward compared to the other groups showing some significant difference between « indifference points » (ANOVA P = 0.032, P = 0.014). When isolating the variable “anorexia” (n = 40) from patients with BN (n = 20), statistically significant differences were also found (P = 0.012, P = 0.004, P = 0.019, P = 0.008), as when isolating the variable “restricting subtype” (n = 20) from patients with bulimia (n = 40 AN-BP and BN) (P = 0.042, P = 0.015). Patients with AN have an unusual ability to delay reward compared to healthy controls and patients with BN. This ability is well enhanced in patients with AN-R compared to patients with AN-BP, and the extreme self-control highlighted by the DD task could constitute an endophenotype of this subtype of anorexia nervosa. As it appears as a diagnostic tool in anorexia nervosa, Delay Discounting could have a prognostic scope in cases of anorexia relapse and cross-over from AN to BN, requiring further longitudinal studies.