It is always an interesting prospect that gene expression patterns in blood may have utility as molecular markers, in this case for Parkinson disease. Using rigorous statistical methods, Clemens Scherzer and colleagues identified a battery of genes whose expression patterns in blood differ in individuals with PD from those without PD. Conceptually, identification of a biomarker phenotype in peripheral blood is clinically very attractive (for identification of PD or any disease or condition), and this study certainly advances the field in this regard and provides the impetus for further study of these identified candidate markers.

It remains unclear, however, what the gene profile is really measuring—this is the “state-versus-trait” issue that plagues most, if not all, biomarker studies. The real question, of course, is whether this or any set of molecular markers can identify individuals with “preclinical” disease. Similar to AD, PD pathology develops over many years, perhaps decades, with clinical manifestations becoming apparent only after significant and substantial...  Read more

It is always an interesting prospect that gene expression patterns in blood may have utility as molecular markers, in this case for Parkinson disease. Using rigorous statistical methods, Clemens Scherzer and colleagues identified a battery of genes whose expression patterns in blood differ in individuals with PD from those without PD. Conceptually, identification of a biomarker phenotype in peripheral blood is clinically very attractive (for identification of PD or any disease or condition), and this study certainly advances the field in this regard and provides the impetus for further study of these identified candidate markers.

It remains unclear, however, what the gene profile is really measuring—this is the “state-versus-trait” issue that plagues most, if not all, biomarker studies. The real question, of course, is whether this or any set of molecular markers can identify individuals with “preclinical” disease. Similar to AD, PD pathology develops over many years, perhaps decades, with clinical manifestations becoming apparent only after significant and substantial neuronal cell death has taken place (estimated to be about 70 percent of vulnerable dopaminergic neurons in PD). For biomarkers to have practical utility, they must be able to identify individuals in the preclinical phases of the disease, before such dramatic neuronal cell death has taken place, in order for putative treatments to have the best chance to preserve normal function in affected individuals. It will be very interesting to see if the molecular signatures identified in this study are able to identify individuals with PD pathology, but prior to the onset of symptoms.

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