When employing the alternative cut-off score ≥ 11, depression was less likely among men with the Met/Met genotype than among men with the Val/Val genotype. Val/Val individuals would be expected to have lower transsynaptic catecholamine levels, due to their high COMT enzyme activity. Such depletion of transsynaptic catecholamine neurotransmitters, like dopamine and noradrenaline, may very well influence susceptibility to depression in this genotype group [3]. Because this association was based on a very small number of cases, it may be incidental, and therefore needs to be interpreted with some caution. Interestingly, however, an association between Val/Val genotype and major depression with early onset has been reported in a multicenter study of various European populations [3]. In contrast to these findings, Ohara et al. found higher frequencies of the Met allele in depressed Asian patients compared with a control group [4]. However, because differences in COMT genotype distribution between ethnic groups are considerable, a finding in one group might not be valid for other groups [23].
