The phenotypic spectrum of parkinson disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, trailing only Alzheimer's disease. This chapter briefly summarizes some of the epidemiological, genetic, and pathophysiological characteristics of PD. The chapter primarily focuses on the clinical features of the illness and thus provides a frame of reference for comparison with the various animal models of PD. Various environmental factors are hypothesized to be operative in the development of PD. Rural living with its agricultural chemical exposure, certain industrial environments, and even occupations such as teaching and medical professions are reported to confer an increased risk for developing PD. Modern molecular genetic techniques have helped investigators identify a growing number of mutations that produce a phenotypic picture of PD. In assessing and developing animal models for PD, researchers must recognize this phenotypic heterogeneity. The perfect animal model that duplicates all the clinical features of PD does not yet exist, and given the complexity of the human disease process, perhaps it is unreasonable to expect one.