The traits and characteristics of a person that are genetic in origin; they are also called familial or said to “run in the family.” Some characteristics that appear to be genetic are instead environmental, the result of shared lifestyle factors among family members, or are activated by environmental triggers. These might range from exposure to chemical toxins to dietary habits. Most scientists believe there are both hereditary, or genetic, and environmental aspects of neurode-generative conditions such as Parkinson’s disease and Alzheimer’s disease.
When Parkinson’s disease “runs in the family,” there are usually several individuals who have it but most family members do not. When there is a family history of Parkinson’s disease, researchers say that there is a genetic predisposition for Parkinson’s disease in the family. This contrasts with MOVEMENT DISORDERS such as HUNTINGTON’S disease, in which anyone who has the gene mutation for the disease will develop the disease and environmental factors are inconsequential to the disease process.