Parkinson’s disease is caused by the deterioration of nerve cells in the brain, but it's still not clear what causes these cells to deteriorate in some people and not others. A new study has found a specific gene mutation linked to the early onset of Parkinson's disease. The team hope the finding could help them better determine an individual's risk for the disease and develop personalized medical care for people with a family history of the disease.

The study, which is now published online in the journal Neurobiology of Aging, found that a gene which produces dopamine in the brain appears to accelerate the onset of Parkinson's disease in Caucasians, particularly in individuals under 50. For example, the average Caucasian with one bad version of this gene developed Parkinson’s symptoms five years earlier and had a 23 percent increased risk for the disease, according to a news release by Iowa State University researchers.

The gene only seems to be a predictor of Parkinson's in younger individuals, and could not be used as a strong predictor of developing Parkinson’s in people over 50.

"As we age, we progressively make less dopamine, and this effect strongly outweighs the genetic influences from the 'bad version' of this gene,” explained Joseph Webb, a graduate research assistant involved in the research, in the news release. According to Webb, because older individuals naturally make less dopamine, the effects of this genetic mutation are not noticeable.

Read: What Causes Parkinson’s Disease?

Parkinson’s disease is a serious disorder of the nervous system that affects around one million Americans. The disease is characterized by gradual problems with movement, often starting with hand tremors before progressing to slurred speech and loss of mobility.

This is not the first time genes have been identified as a factor to the onset of Parkinson's. For example, according to The Mayo Clinic, there are a number of gene variations that increase the risk of Parkinson's disease. However, it must be noted that there is a relatively small risk of Parkinson's disease for each of these genetic markers.

In addition, the Mayo Clinic reports that exposure to certain toxins and environmental factors can increase the risk of developing Parkinson’s later on in life, although this risk is also relatively small. For example, according to The National Parkinson's Foundation, many chemicals used in fields such as welding, farming, military activities and industrial processes have been associated with the disease.

Source: Webb J, WIllette AA, Aging modifies the effect of GCH1 RS11158026 on DAT uptake and Parkinson's disease clinical severity. Neurobiology of Aging . 2016

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