What Causes Parkinson’s Disease? Scientists Discover New Gene Linked to the Disease
Scientists have discovered a new gene linked to Parkinson's disease.
Researchers from the Northwestern University discovered that mutations in a gene identified as TMEM230 can lead to the disease. Scientists provided evidence of the TMEM230 mutations in the study, which is published in Nature Genetics.
Parkinson's disease is a nervous disorder that often starts with hand tremors that eventually wears away motor and non-motor skills until patients have difficulty walking, talking and swallowing. According to the Parkinson's Disease Foundation, about one million people in the United States suffer from Parkinson's - the second most common neurodegenerative disorder next to Alzheimer's.
On Friday, boxing legend Muhammad Ali died after his lengthy battle against Parkinson's disease at age 74. After being diagnosed in 1984, three years after he retired, Parkinson's began to take control of his body, affecting his speech and motor skills.
"Previous research has associated Parkinson's disease with various factors in the environment, but the only direct causes that are known are genetic," Dr. Teepu Siddique, principal investigator in the study and professor at Northwestern University Feinberg School of Medicine, said in a news release.
"Many genes have been claimed to cause Parkinson's disease, but they haven't been validated. We show that mutations in this new gene lead to pathologically and clinically proven cases of the disease," he added.
About 15 percent of Parkinson's disease cases are said to be caused by genetics, particularly by mutations in two genes called SNCA and LRRK2. According to Siddique, the other genes have only been associated with features of parkinsonism, which is a general term for neurological disorders with motor symptoms.
The Discovery of the Gene
In 1996, Siddique and fellow researcher Dr. Han-Xiang Deng began studying a family in which 15 members had symptoms of Parkinson's disease. Symptoms typically include hand tremors, slow movements, stiffness, difficulty in walking and loss of balance.
The researchers used DNA samples and performed genome-wide analyses on 65 of the family's members, including healthy family members and the 13 who had been diagnosed with Parkinson's. The goal was to find one common gene mutation that could form the basis of why a lot of the family members had Parkinson's disease.
After years of studying, the researchers pointed to a small region of DNA on chromosome 20 that contained 141 known genes. They sorted through the genes and compared DNA variations in the healthy family members to those who have the disease. The researchers found over 90,000 variants before eventually singling out TMEM230 as the disease-causing mutated gene.
According to the scientists, TMEM230 encodes a protein that extends across the membrane of tiny sacks inside neurons called synaptic vesicles, which store neurotransmitters before they are released from cell to cell in a process known as vesicle trafficking.
Parkinson's has been associated with low dopamine levels in previous studies, and the scientists believe that the TMEM230 mutation damages dopamine production.
"We believe that vesicle trafficking defects are a key mechanism of Parkinson's disease, not just for cases with this mutation, but a common pathway for the majority of cases. All three of the authenticated genes are concentrated on synaptic vesicles," said Deng.
"Our new findings suggest that normalizing synaptic vesicle trafficking may be a strategy for future therapeutic development. We can develop drugs to promote this critical pathway," he added.
The scientists also discovered mutations in the TMEM230 gene in other Parkinson's disease cases in families in North America and in China.