The effect of COMT Val158 Met genotype on decision-making and preliminary findings on its interaction with the 5-HTTLPR in healthy females

Poor decision-making is inherent to several psychiatric conditions for which a genetic basis may exist. We previously showed that healthy female volunteers homozygous for the short allele (s/s) of the serotonin transporter length polymorphic region (5-HTTLPR) chose more often cards from disadvantageous decks in the Iowa Gambling Task (IGT), which measures decision-making, than long (l) allele carriers. The 5-HTTLPR and catechol-O-methyltransferase (COMT) Val¹⁵⁸ Met polymorphism affect the same set of neuronal structures. Therefore, we explored the effect of the (COMT) Val¹⁵⁸ Met polymorphism on IGT performance and its interaction with the 5-HTTLPR in the same subjects in this study. We observed that subjects homozygous for methionine (Met/Met) chose more disadvantageously than subjects homozygous for valine (Val/Val). s/s-Met/Met-subjects appeared to show the poorest IGT performance of all possible combinations of 5-HTTLPR and COMT allelic variants. Using the Expectancy-Valence model, no differences were found for the three different 5-HTTLPR or COMT genotypes regarding (i) attention to wins versus losses, (ii) updating rate, or (iii) response consistency. However, subjects with at least one Met-allele were paying more attention to wins than subjects with no Met-alleles. We discuss whether a common neuronal mechanism relates to s- and Met-allele-related deficits in updating and/or processing of choice outcome to guide subsequent choices in this gamble-based test.