Table 1 Rationale for genetic markers selected

COMT rs4680

G

G at rs4680 produces valine making the gen product more active in catabolizing dopamine [59]

Reduced cognitive function generally [59] and ADHD [60]

DAT1 intron 8 VNTR

6R

6R leads to more dopamine transporter, less dopamine in the synapse [61] and thus terminates the signal [37]

Increased RT costs for targets in the left hemifield [62] and ADHD [63]

DRD4 rs747302

C

C leads to fewer dopamine receptors via reduced transcription [64]

Association with ADHD [64]

APOE rs429358 + rs7412

ε4

ε4 reduces acetylcholine receptors [65] and may diminish synthesis of acetylcholine [31]

Reduced spatial cueing in visual tasks for middle aged (non-demented) carriers of the ε4 allele [34, 66, 67]

DBH rs1108580

A

DβH converts dopamine to norepinephrine, therefore, the A allele is associated with lower norepinephrine to dopamine ratios [68]

Association with ADHD [69, 70]