The relationship between the Met allele of the BDNF Val66Met polymorphism and impairments in decision making under ambiguity in patients with obsessive–compulsive disorder

Brain‐derived neurotrophic factor (BDNF) gene has an important link to neurotransmitter systems, including serotonin, and seems to play a major role in emotional decision making. Impairment of decision making is an important feature of psychiatric disorders such as obsessive–compulsive disorder (OCD). We explore the link between decision making and the BDNF Val66Met polymorphism, which results in a reduction of BDNF activity, in a sample of Caucasian OCD patients. We used the Iowa Gambling Task (IGT) to measure decision making in 122 OCD patients. All patients were assessed using the Yale–Brown Obsessive–Compulsive Scale, the Beck Depression Inventory, the Beck Anxiety Inventory and the Raven Progressive Matrices. Patients also performed the Continuous Performance Task (CPT‐II) and the Trail Making Test (TMT). We grouped Met‐allele carriers because these act in a dominant way. Met‐allele carries exhibited low performance on both halves of the IGT (first half – F = −2.51, df = 120, P = 0.01; second half – F = −2.32, df = 120, P = 0.02). However, logistic regression analyses showed that the influence of the Met allele seemed to be restricted to the first half of the IGT [first half – β = 0.55, df = 1, P < 0.01, odds ratio (OR) = 5.62; second half – β = 0.32, df = 1, P = 0.15, OR = 2.30]. No differences were observed in tests used to evaluate executive functions associated with the dorsolateral prefrontal cortices (TMT and CPT‐II, df = 120, P > 0.05 for both). Met‐allele impairment may only be related to decisions made under ambiguous conditions. The null results involving TMT and CPT‐II are possibly related to the dysfunction of the orbitofrontal cortices that is associated with OCD.