i think you are wrong... With all do respect, Parkinson's disease biologically speaking is the loss of neurotransmitter which is a result of aging. But these disease is idiopathic and definitely makes Parkinson an unknown cause of its etiology. Normally speaking , Parkinson's disease may result you to Alzheimer and Dementia.
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for internett1t3, you are correct biologically.. But the cause of Parkinson on why dopamine and acetycholine is decreased is unknown.