Dopamine system
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COMT (Val158Met)
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Catechol-o-methyltransferase
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Degradation of catecholamines
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Met variant- carriers have reduced COMT activity
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Prefrontal Cortex
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Differential dopaminergic signaling influences PFC function (COMT-genotype model), may explain different drug effects [58]
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DRD4 (exon 3 VNTR)
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Dopamine receptor D4
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Dopaminergic transmission
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7R-carriers have reduced DRD4 function
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Prefrontal Cortex
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Variation in dopaminergic signaling influences PFC function, interaction with other genotypes [25]
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SLC6A3 (3′UTR VNTR); SLC6A3 (3′UTR VNTR/intron 8 VNTR haplotype)
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Dopamine transporter
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Reuptake of dopamine
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9R- vs. 10R-carriers have reduced or increased DAT availability (inconsistent findings)
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Striatum
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Variability of striatal dopamine Transporter availability influences PFC function directly or indirectly via cortico-striatal pathways [24]
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Serotonin system
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TPH2 (e.g. rs4570625, rs11178997)
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Tryptophan hydroxylase 2
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Synthesis of serotonin
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Influences transcriptional activity
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Raphe nuclei, with ubiquitous action of serotonin
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Differential activity of the cortico-limbic circuit
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Others
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NOS1 exon 1f-VNTR
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Neuronal nitric oxide (NO) synthase
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Synthesis of neuronal NO
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Allelic variation in reporter gene expression
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Striatum
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NO function influences dopamine signaling [32]
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LPHN3 (ADHD risk haplotype)
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Latrophilin
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Adhesion G-protein coupled receptor (?)
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Decreased NAA/Cr ratio in risk haplotype carriers
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Amygdala, caudate nucleus, cerebellum, and cerebral cortex
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Possibly influences dopamine-glutamatergic system interaction
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