Immunocytochemical methods with semi-quantitative computer-assisted densitometry was also applied to identify the reduction of DAT immunoreactivity in PBL from de novo PD patients with respect to healthy controls [81] and patients suffering essential tremor [82], a neurological disorder clinically characterized by postural tremor with slight signs of rigidity that is not accompanied by central DA damage. Here, SLC6A3 is linked to Parkinson disease.