A biological marker, according to the definition of 1998 by the Biomarkers Definitions Working Group of the National Institutes of Health (NIH) in Bethesda (USA), is “something that can be measured quantitatively and that is an indicator either of normal biological functioning or of the presence of a disease or response to a drug treatment.” It can be a gene, a protein, or any other molecule, as well as a morphological or functional characteristic associated with specific physiological or biological mechanisms. A biomarker, in any case, must be sensitive, i.e., able to detect the highest number of patients; specific, i.e., keep false positives to a minimum; accurate, i.e., its measurement must come as close as possible to the true value; precise, i.e., produce a value that can be repeated in subsequent measurements.
In the case of mental illnesses, the use of objective bio markers to accompany the interview with the patient and clinical observation would make it possible to (1) increase diagnostic accuracy since the mere observation of symptoms sometimes does not allow, at least in some stages of the dis ease, to distinguish different pathologies (an example is given by bipolar disorder which, at onset as a depressive phase, can be misdiagnosed as unipolar depression and treated as such); (2) establish a correct diagnosis even at a very early stage of the illness, thus implementing the most suitable treatment as soon as possible; (3) identify individuals at risk and allow effective prevention; (4) immediately identify any relapses or changes in state (depression-mania in bipolar disorder) even before the reappearance of clinical symptoms; and (5) dis cover new potential therapeutic targets.
Currently, however, there are no biomarkers for mental illnesses that already have standardized clinical use, and the reason lies precisely in the complexity of these diseases.
However, there is much scientific evidence that can guide the selection of several factors that could become good bio logical markers.
