This may be a huge leap as an early biomarker of PD:

Early stages of Parkinson disease may be identified by epigenetic changes observed in blood

Parkinson disease, a neurodegenerative disorder in which both genetic and environmental factors play important roles, has been associated with epigenetic changes (those molecular modifications that alter the behavior of genes without changing the DNA sequence). Because accurate diagnosis is not easy for this disease, scientists are continuously trying to identify early signs of the disease that enable treatment before major neurological damage occurs.

In an article published in the October issue of Epigenetics, those epigenetic changes appear to be great candidates as early stage biomarkers for Parkinson Disease.

Researchers from UCSD have now shown that a distinctive pattern of epigenetic modifications (in this case called DNA methylation) is observed in specific genes associated with the disease. Even more interesting, these changes could be easily analyzed in blood samples from patients, which appear to replicate the "epigenetic status" of brain tissue cells, potentially simplifying early diagnosis of the disease.

http://www.medicalnewstoday.com/releases/266633.php