CALB1 and Parkinson disease: The interplay between the presence of calbindin and the progression of PD was initially proposed after the discovery of a subgroup of calbindin-positive dopaminergic neurons that exhibited less pathologic features compared to calbindin-negative dopaminergic neurons in rat substantia nigra pars compacta (SNpc) and postmortem human brain material from PD patients (Gerfen et al., 1985; Yamada et al., 1990).