Parkinson's Disease and Genetics

Approximately 15-20 percent of people with Parkinson's disease have a family history of this disorder. People with a family history of having the disease, have a 3 percent lifetime risk of developing Parkinson’s disease, compared to those with no family history, who have a 1.5 percent lifetime risk.

By studying families with hereditary Parkinson’s disease, scientists have identified several genes that are associated with the disorder. It is not fully understood how genetic changes cause Parkinson disease or influence the risk of developing the disorder. The genes that are so far identified as definitively associated with Parkinson’s disease are:

SNCA (synuclein, alpha non A4 component of amyloid precursor): SNCA makes the protein alpha-synuclein. In brain cells of individuals with Parkinson’s disease, this protein aggregates in clumps called Lewy bodies. Mutations in the SNCA gene are found in early-onset Parkinson’s disease.

PARK2 (Parkinson’s disease autosomal recessive, juvenile 2): The PARK2 gene makes the protein parkin. Mutations of the PARK2 gene are mostly found in individuals with juvenile Parkinson’s disease. Parkin normally helps cells break down and recycle proteins.

PARK7 (Parkinson’s disease autosomal recessive, early onset 7): PARK7 mutations are found in early-onset Parkinson’s disease. The PARK7 gene makes the DJ-1 protein, which may protect cells from oxidative stress.

PINK1 (PTEN-induced putative kinase 1): Mutations of this gene are found in early-onset Parkinson’s disease. The exact function of the protein made by PINK1 is not known, but it may protect structures within the cell called mitochondria from stress.

LRRK2 (leucine-rich repeat kinase 2): LRRK2 makes the protein dardarin. Mutations in the LRRK2 gene have been linked to late-onset Parkinson’s disease.

Alterations in certain genes, including GBA (glucosidase beta acid), SNCAIP (synuclein alpha interacting protein), and UCHL1 (ubiquitin carboxyl-terminal esterase L1) , do not cause Parkinson disease but appear to modify the risk of developing the condition in some families. Variations in other genes that have not been identified probably also contribute to Parkinson disease risk.

Some gene mutations appear to disturb the cell machinery that breaks down unwanted proteins in dopamine-producing neurons. As a result, unprocessed proteins accumulate, leading to the impairment or death of these cells. Other mutations may affect the function of mitochondria, the energy-producing structures within cells. As a byproduct of energy production, mitochondria make molecules called free radicals that can damage cells. Cells normally counteract the effects of free radicals before they cause damage, but mutations can disrupt this process. As a result, free radicals may accumulate and impair or kill dopamine-producing neurons.

In most cases of Parkinson disease, protein deposits called Lewy bodies appear in dead or dying dopamine-producing neurons. It is unclear whether Lewy bodies play a role in killing nerve cells or if they are part of the cells’ response to the disease.

The National Human Genome Research Institute, a division of the National Institutes of Health, has compiled further information about the role of genetics and genetic testing in Parkinson’s disease. Their website is: http://www.genome.gov/10001217#4.