'Parkinson's is a man-made disease'
‘Parkinson’s is a man-made disease’: How a chemical Europe can’t quit may be driving the disease – POLITICO
. . . "was like a lightning bolt," Bloem tells me. "A single chemical had replicated the entire disease. Parkinson's wasn't just bad luck. It could be caused. . . ."

I rarely follow Parkinson's issues but this story caught my eye and I thought you would find it interesting and unnerving . . . :

MPTP (a hellacious catalyst)
MPTP - Wikipedia
". . . of interest as a precursor to the monoaminergic neurotoxin MPP+, which causes permanent symptoms of Parkinson's disease by destroying dopaminergic neurons in the substantia nigra of the brain."

Paraquat Dichloride
Paraquat Dichloride | US EPA

Farmer battles to ban Paraquat, the toxic weed killer linked to Parkinson's
https://www.youtube.com/watch?v=GWxZtwmfnyQ

A small number of a particular molecule and their ability to cause grave harm . . . I don't think this is how the Amyotrophic Lateral Sclerosis develops but a point here is the bad molecule develops because of the otherwise harmless MPTP molecule, or so these articles say.