ICAM1 and Parkinson disease: In line with this, a study using postmortem brain tissues from PD patients and controls, as well as monkeys exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), found over-expression of ICAM-1 in the substantia nigra of patients with PD and in the MPTP monkeys [156].