Preclinical detection in studies of the etiology, natural history, and treatment of Parkinson's disease.

The development of reliable preclinical detection procedures for idiopathic Parkinson's disease may be the fundamental advance required for the establishment of the cause, the natural history, and ultimately, the prevention of this neurodegenerative disorder. The usefulness of these preclinical markers in efforts to better understand the etiology and development of this disorder will relate to whether they are direct measures of dopamine production or indirect measures such as metabolic changes or comorbidity, whether they can be used in the first or later decades of life, whether they are invasive, and whether they are expensive and sophisticated or simple and cheap. An overview of the criteria for evaluation of the utility of specific markers, as well as an assessment of the importance of early markers in future research, is presented.