This type of study illustrates the complexity of how dopamine levels infliuence neurologic activity in that a tonic and phasic dimension is present. Low activity COMT would mean that the tonic dopamine is high, but the phasic dopamine is less clear. In the case of Parkinson's sx, there is clearly not enough dopamine to hit receptors such as DRD3 and DRD3 to keep arms and legs movements suppressed and to more voluntary control (?phasic dopamine?)
How could DRD3 receptor type (A trait) affect this? High levels tonic levels of dopamine as with COMT low activity would increase peripheral suppression of neuromuscular activity in a DRD3 receptor that is sensitive to dopamine (gly/ser). But then high phasic activity could cause erratic activity peripherally. But if dopamine levels and thus tonic activity is at medium level (COMT met/val genotype) and DRD3 receptor is ser/ser, then perhaps phasic activity is more normal when it affects peripheral muscles and nerves??
What we know though based on observations is that Parkinson's is more common in NPA types N/NP and NA-/=
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