The molecular genetics of cognition: dopamine, COMT and BDNF.

The important contribution of genetic factors to the development of cognition and intelligence is widely acknowledged, but identification of these genes has proven to be difficult. Given a variety of evidence implicating the prefrontal cortex and its dopaminergic circuits in cognition, most of the research conducted to date has focused on genes regulating dopaminergic function. Here we review the genetic association studies carried out on catechol-O-methyltransferase (COMT) and the dopamine receptor genes, D1, D2 and D4. In addition, the evidence implicating another promising candidate gene, brain-derived neurotrophic factor (BDNF) in neuropsychological function, is assessed. Both the COMT val158met polymorphism and the BDNF val66met variant appear to influence cognitive function, but the specific neurocognitive processes involved continue to be a matter of debate. Part of the difficulty is distinguishing between false positives, pleiotropy and the influence of a general intelligence factor, g. Also at issue is the complexity of the relevant neuromolecular pathways, which make the inference of simple causal relationships difficult. The implications of molecular genetic cognitive research for psychiatry are discussed in light of these data.