Family Tree & Parkinson's Disease

Parkinson's disease, or PD, is a progressive neurological disorder in which damaged brain cells impair movement and muscle control. According to the Parkinson's Disease Foundation, the disorder typically develops after age 55 and affects 4 million to 6 million people worldwide. Researchers have isolated a gene that causes one type of PD in some families, but only about 2 percent of all cases are inherited. Further genetic research may help clarify the role that family history and other risk factors play in the development of the disorder.

Family History

• Experts believe family history is a risk factor for Parkinson's disease but is not a predictor of the illness.

  Experts debate the importance of family history as a risk factor for Parkinson's disease. The National Institute of Neurological Disorders and Stroke estimates that 15 to 25 percent of people with PD have a known relative with the disease, but more than half of these cases involve the rare, early-onset form of the illness. In typical cases, family history is a poor predictor for PD, although the risk may be slightly higher if the relative is a sibling rather than a parent or other family member.

Genetics

• Genetics is the study of the information inside each cell of the human body.

  Genetic studies help scientists learn which genes (the basic "information units" of human DNA) and gene mutations (other forms of the same gene) are associated with Parkinson's disease. The human body's 20,000 to 25,000 genes determine traits such as hair color, height and blood type, as well as enable the body to perform necessary tasks. Certain genes affect the likelihood of developing an illness.

Significance

• Scientists have yet to determine exactly how certain genes work with other factors to cause Parkinson's disease.

  Scientists have discovered 13 genes associated with Parkinson's disease, but it remains unclear as to exactly how genetics influence who does and does not develop the illness. Only one gene is considered "causal," meaning its presence alone is enough to guarantee that an individual will eventually suffer Parkinson's disease. According to the Parkinson's Disease Foundation, this type of gene is rare, accounting for just a small minority of PD cases.

Misconceptions

• Families who live in rural areas face an increased risk of developing Parkinson's disease.

  Scientists are reconsidering previously accepted ideas about Parkinson's disease. In the past, they would study generations of the same family to find a pattern; if no pattern existed, they would conclude that genes played no part in the illness. Now, however, scientists understand that both excessive drinking of well water and exposure to certain pesticides and herbicides increase the occurrence of the disease, meaning that families who have farmed or lived in rural areas for generations may be at increased risk despite the lack of a hereditary pattern.

Genetic Testing

• The doctor's office you visit may have genetic professionals on staff to answer questions about genetic testing.

  Genetic testing for the PINK1 gene, known to cause Parkinson's disease in some people, is now available. Usually, however, health care professionals do not advise such testing because the PINK1 gene is responsible for only 2 percent of early-onset PD cases. The National Human Genome Research Institute agrees that genetic testing for PD is of limited usefulness, but it advises people to speak with a doctor or genetic professional if they need more information to make a decision.