Biomarkers

A PET scan of a human brainImage copywrite public domainA biomarker is any characteristic that can be objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to therapeutic interventions. This may include measures of biochemical components in body fluids and tissues, as well as imaging, physiological, and clinical measures. 

Biomarkers that can be measured with minimally invasive methods are of particular interest for use in clinical trials of therapeutics. They are critical tools for clinical development that can be used for appropriate patient selection, guiding dosing strategies, or as a measure of efficacy.

Types of biomarkers include objective markers that assist in diagnosis, measures of disease progression that change with the disease, or specific measures of drug action. Measurement methods include biochemical examination of tissues and fluids, functional imaging methods, neurophysiological measures of muscle function (Valls-Sole and Valldeoriola, 2002), transcranial ultrasound (Berg et al., 2001; Walter et al., 2002; Mehta et al., 2008; Berg 2006), and assays of olfactory function.

It is important to note that by the time people with Parkinson's disease develop the cardinal motor symptoms, approximately 80% of dopamine neurons have been lost in the nigrostriatal pathway. The identification of biomarkers that track the disease process in this 'pre-motor' stage would allow earlier identification of at-risk individuals.