Table 1.

Catechol-O-methyltransferase COMT enzyme and its three phenotypes activities (COMT-475G > A or rs4680 G > A or Met158Val gene polymorphism).

Homozygous COMT G/G	Homozygous Val158val	Enzyme with high activity	Low level of dopamine
Heterozygous COMT A/G	Heterozygous Val158Met	Enzyme with medium activity	Medium level of dopamine
Homozygous COMT A/A	Homozygous Met158met	Enzyme with low activity	High level of dopamine