GRP78 is expressed in photoreceptors, including their outer segments [90,91], and attenuated levels of this protein have been documented in the brain of PD patients [86] and the cortex of Park2 KO mice [55], this pointing out to the dysfunction of a neuroprotective mechanism additional to HSC70 in our MPTP-treated monkeys. The gene discussed is HSPA5; the disease is Parkinson disease.