Causes

Most Parkinson’s disease cases are sporadic; genetic factors and family history haven’t been the specific cause in the onset of the disease. However genetic factors can be linked to Parkinson’s in a small proportion of cases. It is thought that for most cases the cause is a combination of genetic and environmental factors.

Genetic Factors:

Around 15 percent of people with Parkinson disease have a family history of this disorder. 13 genes have been identified that are associated with Parkinson’s and may cause the disease in a small number of families. These genes involve proteins that play a role in dopamine cell functions.

These genes include LRRK2, PARK2, PARK7, PINK1 and SNCA but it isn’t fully understood how mutations in these genes cause Parkinson’s disease.

Image courtesy of https://en.wikipedia.org/wiki/File:Protein_PARK2_PDB_1iyf.png

Some mutations may involve free radicals, which are a byproduct of ATP production by mitochondria. The cell normally neutralizes these free radicals but mutations in these genes may stop the neutralization process. If the free radicals aren’t neutralized they may damage or kill dopamine-producing neurons.

Other mutations disturb the cell processes that degrade unwanted proteins. This leads to proteins that haven’t been degraded accumulating which can lead to the impairment or death of dopamine-producing neurons.

Environmental Factors:

There is evidence that environmental factors may cause dopamine-producing neurons to die, leading to the development of Parkinson's.

Factors that have been linked to Parkinson’s disease are rural living, well water, herbicide use and exposure to pesticides.

The toxin 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) is known to induce the symptoms of Parkinson’s in humans. MPTP’s chemical structure is very similair to the herbicide paraquat and damages cells in a similar way to the pesticide rotenone. 

Image courtesy of https://en.wikipedia.org/wiki/File:Cropduster_spraying_pesticides.jpg