In most cases, there is no way to predict or prevent sporadic PD. However, researchers are looking for a biomarker—a biological abnormality that all people with PD might share—that could be detected by screening techniques or by a simple chemical test given to people who do not yet have any parkinsonian symptoms. This could help doctors identify people at risk of the disease. It also might allow them to find treatments that will stop the disease process in the early stages. Studies demonstrated that synuclein builds up in nerve cells years before symptoms occur. Loss of a sense of smell, constipation, restless legs, and REM sleep disorder are potentially caused by these early changes.