Genomic and proteomic biomarkers for Parkinson disease.

Biomarkers are objective, accessible, and easily measurable biologic parameters that correlate either with the presence (trait) or the severity (state) of a disease. As the major neurodegenerative diseases, such as Alzheimer disease or Parkinson disease, are likely to be etiologically heterogeneous disorders, sensitive and reliable biomarkers that reflect the underlying disease process are urgently needed, and are a prerequisite for a more refined diagnosis and the development of novel disease-modifying therapeutic strategies. "Genetic biomarkers," in the form of disease genes or risk-modifying variants, are able to define the risk of an individual developing a disease, and allow stratification of patient populations according to the underlying molecular defect. Alterations of the transcriptome or the proteome, on the other hand, may provide a means to monitor disease progression or severity. However, because of the complex relationship of genotypes and phenotypes in neurodegenerative disorders, the development of useful biomarkers is still in an early phase.