For the discussion that follows next, it is important to consider the results of one negative meta-analysis. We recently conducted a meta-analysis of case-control genetic association studies of the COMT Val158/108 Met polymorphism in healthy control groups and clinically diagnosed schizophrenia patients (Munafo et al. 2005). The COMT gene has been regarded as a promising candidate gene for schizophrenia for some time, as it is the gene coding for the catechol O-methyltransferase enzyme, which inactivates catechols at post-synaptic sites in the human brain. COMT contains a functional polymorphism, a single nucleotide polymorphism at position 158/108 that results in a change from valine (Val) to methionine (Met) (Chen et al. 2004).
