The specific causes of Parkinson’s disease (PD) remain unknown. Our understanding is that PD develops from several risk factors including aging, genetic predisposition, and environmental toxins. The common effect of these factors is that they lead to damage to nerve cells that produce dopamine and norepinephrine to control muscle movement. Dopamine transmits nerve impulses to produce smooth movement of voluntary muscles, and loss of the chemical impairs nerve impulses, resulting in shaking or tremors. Patients with Parkinson’s retain less than 40 percent the normal number of cells that produce dopamine. Norepinephrine operates in a similar way as dopamine to control autonomic functions such as heartbeat and blood pressure.
Age is considered the most important risk factor in PD, with most cases beginning in people at an average age of 60. Cases of early-onset Parkinson’s are associated with heredity, and have been linked to mutations in several genes. Research also indicates contact with toxins and other environmental factors may be causes of Parkinson’s. The patient’s sex seems to play a role as PD affects 50 percent more men than women, although the reason is not known. Known gene mutations related to PD include those affecting the parkin, PINK1 and DJ-1 genes.
Other possible causes of Parkinson’s include viruses such as influenza (post-encephalitic parkinsonism), overproduction of free radicals that damage cells, build-ups of proteins that kill nerve cells, and neurotoxins such as MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine).