First, the age is aging. Parkinson's disease mainly occurs in middle-aged and elderly people, and rarely occurs before the age of 40, suggesting that aging is related to the onset. However, it is found that the dopamine content in substantia nigra of normal people decreases with age after 30 years old, while Parkinson's disease only occurs in a few normal elderly people, so aging is not the only factor of Parkinson's disease.
Second, environmental factors. It is found that there is a neurotoxic substance in synthetic heroin used by drug addicts, which can selectively enter dopaminergic neurons in substantia nigra, inhibit the activity of mitochondrial respiratory chain complex I, promote oxidative stress, and lead to degeneration and death of dopaminergic neurons. It is suggested that mitochondrial dysfunction may be one of the pathogenic factors of Parkinson's disease.
Third, genetic factors. Parkinson's disease is concentrated in some families. It is reported that about 10% patients with Parkinson's disease have a family history, which is autosomal dominant inheritance with low penetrance. Some studies also believe that it conforms to polygenic inheritance, so genetic factors may increase the susceptibility to illness.