Polymorphism of the brain-derived neurotrophic factor gene and performance on a cognitive prefrontal test in bipolar patients

Objectives: The aim of the study was to test a possible association between the Val66Met polymorphism of the brain-derived neurotrophic factor (BDNF) gene and performance on a neurocognitive test, the Wisconsin Card Sorting Test (WCST), in bipolar patients. Methods: Fifty-four bipolar patients were studied, 18 male and 36 female, aged 18-72 (mean 46 years). The number of perseverative errors (WCST-P), non-perseverative errors (WCST-NP), completed corrected categories (WCST-CC), conceptual level responses (WCST-%CONC) and set to the first category (WCST-1st CAT) were measured in relation to the Val66Met genotypes of BDNF. Results: The percentages of subjects with Val/Val, Val/Met and Met/Met genotypes were respectively 81.5, 16.7 and 1.8%. Subjects with Val/Val and Val/Met genotypes did not differ on clinical factors except for the age of onset of the illness, which was earlier in Val/Val than Val/Met genotype (27 years versus 38 years). The performance in all domains of WCST was significantly better in subjects with Val/Val BDNF genotype compared with Val/Met genotype. Conclusions: The results suggest a role of BDNF in prefrontal cognitive function in bipolar illness. The tests of prefrontal cognition may be considered as endophenotypic markers in bipolar illness.