So far, most biomarker studies using miRNAs have focused on the differentiation of sPD patients from healthy controls (HC), while in the present proof-of-concept study we aimed to test how well extracellular miRNAs can be used to reliably differentiate between sPD patients and LRRK2 mutation carriers (LRRK2MC). The gene discussed is LRRK2; the disease is Platelet storage pool disease.